1 // SPDX-License-Identifier: GPL-2.0-only
3 * linux/kernel/printk.c
5 * Copyright (C) 1991, 1992 Linus Torvalds
7 * Modified to make sys_syslog() more flexible: added commands to
8 * return the last 4k of kernel messages, regardless of whether
9 * they've been read or not. Added option to suppress kernel printk's
10 * to the console. Added hook for sending the console messages
11 * elsewhere, in preparation for a serial line console (someday).
13 * Modified for sysctl support, 1/8/97, Chris Horn.
14 * Fixed SMP synchronization, 08/08/99, Manfred Spraul
15 * manfred@colorfullife.com
16 * Rewrote bits to get rid of console_lock
17 * 01Mar01 Andrew Morton
20 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
22 #include <linux/kernel.h>
24 #include <linux/tty.h>
25 #include <linux/tty_driver.h>
26 #include <linux/console.h>
27 #include <linux/init.h>
28 #include <linux/jiffies.h>
29 #include <linux/nmi.h>
30 #include <linux/module.h>
31 #include <linux/moduleparam.h>
32 #include <linux/delay.h>
33 #include <linux/smp.h>
34 #include <linux/security.h>
35 #include <linux/memblock.h>
36 #include <linux/syscalls.h>
37 #include <linux/crash_core.h>
38 #include <linux/ratelimit.h>
39 #include <linux/kmsg_dump.h>
40 #include <linux/syslog.h>
41 #include <linux/cpu.h>
42 #include <linux/rculist.h>
43 #include <linux/poll.h>
44 #include <linux/irq_work.h>
45 #include <linux/ctype.h>
46 #include <linux/uio.h>
47 #include <linux/sched/clock.h>
48 #include <linux/sched/debug.h>
49 #include <linux/sched/task_stack.h>
51 #include <linux/uaccess.h>
52 #include <asm/sections.h>
54 #include <trace/events/initcall.h>
55 #define CREATE_TRACE_POINTS
56 #include <trace/events/printk.h>
58 #include "printk_ringbuffer.h"
59 #include "console_cmdline.h"
63 int console_printk
[4] = {
64 CONSOLE_LOGLEVEL_DEFAULT
, /* console_loglevel */
65 MESSAGE_LOGLEVEL_DEFAULT
, /* default_message_loglevel */
66 CONSOLE_LOGLEVEL_MIN
, /* minimum_console_loglevel */
67 CONSOLE_LOGLEVEL_DEFAULT
, /* default_console_loglevel */
69 EXPORT_SYMBOL_GPL(console_printk
);
71 atomic_t ignore_console_lock_warning __read_mostly
= ATOMIC_INIT(0);
72 EXPORT_SYMBOL(ignore_console_lock_warning
);
75 * Low level drivers may need that to know if they can schedule in
76 * their unblank() callback or not. So let's export it.
79 EXPORT_SYMBOL(oops_in_progress
);
82 * console_sem protects the console_drivers list, and also
83 * provides serialisation for access to the entire console
86 static DEFINE_SEMAPHORE(console_sem
);
87 struct console
*console_drivers
;
88 EXPORT_SYMBOL_GPL(console_drivers
);
91 * System may need to suppress printk message under certain
92 * circumstances, like after kernel panic happens.
94 int __read_mostly suppress_printk
;
97 static struct lockdep_map console_lock_dep_map
= {
98 .name
= "console_lock"
102 enum devkmsg_log_bits
{
103 __DEVKMSG_LOG_BIT_ON
= 0,
104 __DEVKMSG_LOG_BIT_OFF
,
105 __DEVKMSG_LOG_BIT_LOCK
,
108 enum devkmsg_log_masks
{
109 DEVKMSG_LOG_MASK_ON
= BIT(__DEVKMSG_LOG_BIT_ON
),
110 DEVKMSG_LOG_MASK_OFF
= BIT(__DEVKMSG_LOG_BIT_OFF
),
111 DEVKMSG_LOG_MASK_LOCK
= BIT(__DEVKMSG_LOG_BIT_LOCK
),
114 /* Keep both the 'on' and 'off' bits clear, i.e. ratelimit by default: */
115 #define DEVKMSG_LOG_MASK_DEFAULT 0
117 static unsigned int __read_mostly devkmsg_log
= DEVKMSG_LOG_MASK_DEFAULT
;
119 static int __control_devkmsg(char *str
)
126 len
= str_has_prefix(str
, "on");
128 devkmsg_log
= DEVKMSG_LOG_MASK_ON
;
132 len
= str_has_prefix(str
, "off");
134 devkmsg_log
= DEVKMSG_LOG_MASK_OFF
;
138 len
= str_has_prefix(str
, "ratelimit");
140 devkmsg_log
= DEVKMSG_LOG_MASK_DEFAULT
;
147 static int __init
control_devkmsg(char *str
)
149 if (__control_devkmsg(str
) < 0)
153 * Set sysctl string accordingly:
155 if (devkmsg_log
== DEVKMSG_LOG_MASK_ON
)
156 strcpy(devkmsg_log_str
, "on");
157 else if (devkmsg_log
== DEVKMSG_LOG_MASK_OFF
)
158 strcpy(devkmsg_log_str
, "off");
159 /* else "ratelimit" which is set by default. */
162 * Sysctl cannot change it anymore. The kernel command line setting of
163 * this parameter is to force the setting to be permanent throughout the
164 * runtime of the system. This is a precation measure against userspace
165 * trying to be a smarta** and attempting to change it up on us.
167 devkmsg_log
|= DEVKMSG_LOG_MASK_LOCK
;
171 __setup("printk.devkmsg=", control_devkmsg
);
173 char devkmsg_log_str
[DEVKMSG_STR_MAX_SIZE
] = "ratelimit";
175 int devkmsg_sysctl_set_loglvl(struct ctl_table
*table
, int write
,
176 void *buffer
, size_t *lenp
, loff_t
*ppos
)
178 char old_str
[DEVKMSG_STR_MAX_SIZE
];
183 if (devkmsg_log
& DEVKMSG_LOG_MASK_LOCK
)
187 strncpy(old_str
, devkmsg_log_str
, DEVKMSG_STR_MAX_SIZE
);
190 err
= proc_dostring(table
, write
, buffer
, lenp
, ppos
);
195 err
= __control_devkmsg(devkmsg_log_str
);
198 * Do not accept an unknown string OR a known string with
201 if (err
< 0 || (err
+ 1 != *lenp
)) {
203 /* ... and restore old setting. */
205 strncpy(devkmsg_log_str
, old_str
, DEVKMSG_STR_MAX_SIZE
);
214 /* Number of registered extended console drivers. */
215 static int nr_ext_console_drivers
;
218 * Helper macros to handle lockdep when locking/unlocking console_sem. We use
219 * macros instead of functions so that _RET_IP_ contains useful information.
221 #define down_console_sem() do { \
223 mutex_acquire(&console_lock_dep_map, 0, 0, _RET_IP_);\
226 static int __down_trylock_console_sem(unsigned long ip
)
232 * Here and in __up_console_sem() we need to be in safe mode,
233 * because spindump/WARN/etc from under console ->lock will
234 * deadlock in printk()->down_trylock_console_sem() otherwise.
236 printk_safe_enter_irqsave(flags
);
237 lock_failed
= down_trylock(&console_sem
);
238 printk_safe_exit_irqrestore(flags
);
242 mutex_acquire(&console_lock_dep_map
, 0, 1, ip
);
245 #define down_trylock_console_sem() __down_trylock_console_sem(_RET_IP_)
247 static void __up_console_sem(unsigned long ip
)
251 mutex_release(&console_lock_dep_map
, ip
);
253 printk_safe_enter_irqsave(flags
);
255 printk_safe_exit_irqrestore(flags
);
257 #define up_console_sem() __up_console_sem(_RET_IP_)
260 * This is used for debugging the mess that is the VT code by
261 * keeping track if we have the console semaphore held. It's
262 * definitely not the perfect debug tool (we don't know if _WE_
263 * hold it and are racing, but it helps tracking those weird code
264 * paths in the console code where we end up in places I want
265 * locked without the console sempahore held).
267 static int console_locked
, console_suspended
;
270 * If exclusive_console is non-NULL then only this console is to be printed to.
272 static struct console
*exclusive_console
;
275 * Array of consoles built from command line options (console=)
278 #define MAX_CMDLINECONSOLES 8
280 static struct console_cmdline console_cmdline
[MAX_CMDLINECONSOLES
];
282 static int preferred_console
= -1;
283 static bool has_preferred_console
;
284 int console_set_on_cmdline
;
285 EXPORT_SYMBOL(console_set_on_cmdline
);
287 /* Flag: console code may call schedule() */
288 static int console_may_schedule
;
290 enum con_msg_format_flags
{
291 MSG_FORMAT_DEFAULT
= 0,
292 MSG_FORMAT_SYSLOG
= (1 << 0),
295 static int console_msg_format
= MSG_FORMAT_DEFAULT
;
298 * The printk log buffer consists of a sequenced collection of records, each
299 * containing variable length message text. Every record also contains its
300 * own meta-data (@info).
302 * Every record meta-data carries the timestamp in microseconds, as well as
303 * the standard userspace syslog level and syslog facility. The usual kernel
304 * messages use LOG_KERN; userspace-injected messages always carry a matching
305 * syslog facility, by default LOG_USER. The origin of every message can be
306 * reliably determined that way.
308 * The human readable log message of a record is available in @text, the
309 * length of the message text in @text_len. The stored message is not
312 * Optionally, a record can carry a dictionary of properties (key/value
313 * pairs), to provide userspace with a machine-readable message context.
315 * Examples for well-defined, commonly used property names are:
316 * DEVICE=b12:8 device identifier
320 * +sound:card0 subsystem:devname
321 * SUBSYSTEM=pci driver-core subsystem name
323 * Valid characters in property names are [a-zA-Z0-9.-_]. Property names
324 * and values are terminated by a '\0' character.
326 * Example of record values:
327 * record.text_buf = "it's a line" (unterminated)
328 * record.info.seq = 56
329 * record.info.ts_nsec = 36863
330 * record.info.text_len = 11
331 * record.info.facility = 0 (LOG_KERN)
332 * record.info.flags = 0
333 * record.info.level = 3 (LOG_ERR)
334 * record.info.caller_id = 299 (task 299)
335 * record.info.dev_info.subsystem = "pci" (terminated)
336 * record.info.dev_info.device = "+pci:0000:00:01.0" (terminated)
338 * The 'struct printk_info' buffer must never be directly exported to
339 * userspace, it is a kernel-private implementation detail that might
340 * need to be changed in the future, when the requirements change.
342 * /dev/kmsg exports the structured data in the following line format:
343 * "<level>,<sequnum>,<timestamp>,<contflag>[,additional_values, ... ];<message text>\n"
345 * Users of the export format should ignore possible additional values
346 * separated by ',', and find the message after the ';' character.
348 * The optional key/value pairs are attached as continuation lines starting
349 * with a space character and terminated by a newline. All possible
350 * non-prinatable characters are escaped in the "\xff" notation.
354 LOG_NEWLINE
= 2, /* text ended with a newline */
355 LOG_CONT
= 8, /* text is a fragment of a continuation line */
359 * The logbuf_lock protects kmsg buffer, indices, counters. This can be taken
360 * within the scheduler's rq lock. It must be released before calling
361 * console_unlock() or anything else that might wake up a process.
363 DEFINE_RAW_SPINLOCK(logbuf_lock
);
366 * Helper macros to lock/unlock logbuf_lock and switch between
367 * printk-safe/unsafe modes.
369 #define logbuf_lock_irq() \
371 printk_safe_enter_irq(); \
372 raw_spin_lock(&logbuf_lock); \
375 #define logbuf_unlock_irq() \
377 raw_spin_unlock(&logbuf_lock); \
378 printk_safe_exit_irq(); \
381 #define logbuf_lock_irqsave(flags) \
383 printk_safe_enter_irqsave(flags); \
384 raw_spin_lock(&logbuf_lock); \
387 #define logbuf_unlock_irqrestore(flags) \
389 raw_spin_unlock(&logbuf_lock); \
390 printk_safe_exit_irqrestore(flags); \
394 DECLARE_WAIT_QUEUE_HEAD(log_wait
);
395 /* the next printk record to read by syslog(READ) or /proc/kmsg */
396 static u64 syslog_seq
;
397 static size_t syslog_partial
;
398 static bool syslog_time
;
400 /* the next printk record to write to the console */
401 static u64 console_seq
;
402 static u64 exclusive_console_stop_seq
;
403 static unsigned long console_dropped
;
405 /* the next printk record to read after the last 'clear' command */
406 static u64 clear_seq
;
408 #ifdef CONFIG_PRINTK_CALLER
409 #define PREFIX_MAX 48
411 #define PREFIX_MAX 32
413 #define LOG_LINE_MAX (1024 - PREFIX_MAX)
415 #define LOG_LEVEL(v) ((v) & 0x07)
416 #define LOG_FACILITY(v) ((v) >> 3 & 0xff)
419 #define LOG_ALIGN __alignof__(unsigned long)
420 #define __LOG_BUF_LEN (1 << CONFIG_LOG_BUF_SHIFT)
421 #define LOG_BUF_LEN_MAX (u32)(1 << 31)
422 static char __log_buf
[__LOG_BUF_LEN
] __aligned(LOG_ALIGN
);
423 static char *log_buf
= __log_buf
;
424 static u32 log_buf_len
= __LOG_BUF_LEN
;
427 * Define the average message size. This only affects the number of
428 * descriptors that will be available. Underestimating is better than
429 * overestimating (too many available descriptors is better than not enough).
431 #define PRB_AVGBITS 5 /* 32 character average length */
433 #if CONFIG_LOG_BUF_SHIFT <= PRB_AVGBITS
434 #error CONFIG_LOG_BUF_SHIFT value too small.
436 _DEFINE_PRINTKRB(printk_rb_static
, CONFIG_LOG_BUF_SHIFT
- PRB_AVGBITS
,
437 PRB_AVGBITS
, &__log_buf
[0]);
439 static struct printk_ringbuffer printk_rb_dynamic
;
441 static struct printk_ringbuffer
*prb
= &printk_rb_static
;
444 * We cannot access per-CPU data (e.g. per-CPU flush irq_work) before
445 * per_cpu_areas are initialised. This variable is set to true when
446 * it's safe to access per-CPU data.
448 static bool __printk_percpu_data_ready __read_mostly
;
450 bool printk_percpu_data_ready(void)
452 return __printk_percpu_data_ready
;
455 /* Return log buffer address */
456 char *log_buf_addr_get(void)
461 /* Return log buffer size */
462 u32
log_buf_len_get(void)
468 * Define how much of the log buffer we could take at maximum. The value
469 * must be greater than two. Note that only half of the buffer is available
470 * when the index points to the middle.
472 #define MAX_LOG_TAKE_PART 4
473 static const char trunc_msg
[] = "<truncated>";
475 static void truncate_msg(u16
*text_len
, u16
*trunc_msg_len
)
478 * The message should not take the whole buffer. Otherwise, it might
479 * get removed too soon.
481 u32 max_text_len
= log_buf_len
/ MAX_LOG_TAKE_PART
;
483 if (*text_len
> max_text_len
)
484 *text_len
= max_text_len
;
486 /* enable the warning message (if there is room) */
487 *trunc_msg_len
= strlen(trunc_msg
);
488 if (*text_len
>= *trunc_msg_len
)
489 *text_len
-= *trunc_msg_len
;
494 int dmesg_restrict
= IS_ENABLED(CONFIG_SECURITY_DMESG_RESTRICT
);
496 static int syslog_action_restricted(int type
)
501 * Unless restricted, we allow "read all" and "get buffer size"
504 return type
!= SYSLOG_ACTION_READ_ALL
&&
505 type
!= SYSLOG_ACTION_SIZE_BUFFER
;
508 static int check_syslog_permissions(int type
, int source
)
511 * If this is from /proc/kmsg and we've already opened it, then we've
512 * already done the capabilities checks at open time.
514 if (source
== SYSLOG_FROM_PROC
&& type
!= SYSLOG_ACTION_OPEN
)
517 if (syslog_action_restricted(type
)) {
518 if (capable(CAP_SYSLOG
))
521 * For historical reasons, accept CAP_SYS_ADMIN too, with
524 if (capable(CAP_SYS_ADMIN
)) {
525 pr_warn_once("%s (%d): Attempt to access syslog with "
526 "CAP_SYS_ADMIN but no CAP_SYSLOG "
528 current
->comm
, task_pid_nr(current
));
534 return security_syslog(type
);
537 static void append_char(char **pp
, char *e
, char c
)
543 static ssize_t
info_print_ext_header(char *buf
, size_t size
,
544 struct printk_info
*info
)
546 u64 ts_usec
= info
->ts_nsec
;
548 #ifdef CONFIG_PRINTK_CALLER
549 u32 id
= info
->caller_id
;
551 snprintf(caller
, sizeof(caller
), ",caller=%c%u",
552 id
& 0x80000000 ? 'C' : 'T', id
& ~0x80000000);
557 do_div(ts_usec
, 1000);
559 return scnprintf(buf
, size
, "%u,%llu,%llu,%c%s;",
560 (info
->facility
<< 3) | info
->level
, info
->seq
,
561 ts_usec
, info
->flags
& LOG_CONT
? 'c' : '-', caller
);
564 static ssize_t
msg_add_ext_text(char *buf
, size_t size
,
565 const char *text
, size_t text_len
,
568 char *p
= buf
, *e
= buf
+ size
;
571 /* escape non-printable characters */
572 for (i
= 0; i
< text_len
; i
++) {
573 unsigned char c
= text
[i
];
575 if (c
< ' ' || c
>= 127 || c
== '\\')
576 p
+= scnprintf(p
, e
- p
, "\\x%02x", c
);
578 append_char(&p
, e
, c
);
580 append_char(&p
, e
, endc
);
585 static ssize_t
msg_add_dict_text(char *buf
, size_t size
,
586 const char *key
, const char *val
)
588 size_t val_len
= strlen(val
);
594 len
= msg_add_ext_text(buf
, size
, "", 0, ' '); /* dict prefix */
595 len
+= msg_add_ext_text(buf
+ len
, size
- len
, key
, strlen(key
), '=');
596 len
+= msg_add_ext_text(buf
+ len
, size
- len
, val
, val_len
, '\n');
601 static ssize_t
msg_print_ext_body(char *buf
, size_t size
,
602 char *text
, size_t text_len
,
603 struct dev_printk_info
*dev_info
)
607 len
= msg_add_ext_text(buf
, size
, text
, text_len
, '\n');
612 len
+= msg_add_dict_text(buf
+ len
, size
- len
, "SUBSYSTEM",
613 dev_info
->subsystem
);
614 len
+= msg_add_dict_text(buf
+ len
, size
- len
, "DEVICE",
620 /* /dev/kmsg - userspace message inject/listen interface */
621 struct devkmsg_user
{
623 struct ratelimit_state rs
;
625 char buf
[CONSOLE_EXT_LOG_MAX
];
627 struct printk_info info
;
628 char text_buf
[CONSOLE_EXT_LOG_MAX
];
629 struct printk_record record
;
632 static __printf(3, 4) __cold
633 int devkmsg_emit(int facility
, int level
, const char *fmt
, ...)
639 r
= vprintk_emit(facility
, level
, NULL
, fmt
, args
);
645 static ssize_t
devkmsg_write(struct kiocb
*iocb
, struct iov_iter
*from
)
648 int level
= default_message_loglevel
;
649 int facility
= 1; /* LOG_USER */
650 struct file
*file
= iocb
->ki_filp
;
651 struct devkmsg_user
*user
= file
->private_data
;
652 size_t len
= iov_iter_count(from
);
655 if (!user
|| len
> LOG_LINE_MAX
)
658 /* Ignore when user logging is disabled. */
659 if (devkmsg_log
& DEVKMSG_LOG_MASK_OFF
)
662 /* Ratelimit when not explicitly enabled. */
663 if (!(devkmsg_log
& DEVKMSG_LOG_MASK_ON
)) {
664 if (!___ratelimit(&user
->rs
, current
->comm
))
668 buf
= kmalloc(len
+1, GFP_KERNEL
);
673 if (!copy_from_iter_full(buf
, len
, from
)) {
679 * Extract and skip the syslog prefix <[0-9]*>. Coming from userspace
680 * the decimal value represents 32bit, the lower 3 bit are the log
681 * level, the rest are the log facility.
683 * If no prefix or no userspace facility is specified, we
684 * enforce LOG_USER, to be able to reliably distinguish
685 * kernel-generated messages from userspace-injected ones.
688 if (line
[0] == '<') {
692 u
= simple_strtoul(line
+ 1, &endp
, 10);
693 if (endp
&& endp
[0] == '>') {
694 level
= LOG_LEVEL(u
);
695 if (LOG_FACILITY(u
) != 0)
696 facility
= LOG_FACILITY(u
);
703 devkmsg_emit(facility
, level
, "%s", line
);
708 static ssize_t
devkmsg_read(struct file
*file
, char __user
*buf
,
709 size_t count
, loff_t
*ppos
)
711 struct devkmsg_user
*user
= file
->private_data
;
712 struct printk_record
*r
= &user
->record
;
719 ret
= mutex_lock_interruptible(&user
->lock
);
724 if (!prb_read_valid(prb
, user
->seq
, r
)) {
725 if (file
->f_flags
& O_NONBLOCK
) {
732 ret
= wait_event_interruptible(log_wait
,
733 prb_read_valid(prb
, user
->seq
, r
));
739 if (user
->seq
< prb_first_valid_seq(prb
)) {
740 /* our last seen message is gone, return error and reset */
741 user
->seq
= prb_first_valid_seq(prb
);
747 len
= info_print_ext_header(user
->buf
, sizeof(user
->buf
), r
->info
);
748 len
+= msg_print_ext_body(user
->buf
+ len
, sizeof(user
->buf
) - len
,
749 &r
->text_buf
[0], r
->info
->text_len
,
752 user
->seq
= r
->info
->seq
+ 1;
760 if (copy_to_user(buf
, user
->buf
, len
)) {
766 mutex_unlock(&user
->lock
);
771 * Be careful when modifying this function!!!
773 * Only few operations are supported because the device works only with the
774 * entire variable length messages (records). Non-standard values are
775 * returned in the other cases and has been this way for quite some time.
776 * User space applications might depend on this behavior.
778 static loff_t
devkmsg_llseek(struct file
*file
, loff_t offset
, int whence
)
780 struct devkmsg_user
*user
= file
->private_data
;
791 /* the first record */
792 user
->seq
= prb_first_valid_seq(prb
);
796 * The first record after the last SYSLOG_ACTION_CLEAR,
797 * like issued by 'dmesg -c'. Reading /dev/kmsg itself
798 * changes no global state, and does not clear anything.
800 user
->seq
= clear_seq
;
803 /* after the last record */
804 user
->seq
= prb_next_seq(prb
);
813 static __poll_t
devkmsg_poll(struct file
*file
, poll_table
*wait
)
815 struct devkmsg_user
*user
= file
->private_data
;
819 return EPOLLERR
|EPOLLNVAL
;
821 poll_wait(file
, &log_wait
, wait
);
824 if (prb_read_valid(prb
, user
->seq
, NULL
)) {
825 /* return error when data has vanished underneath us */
826 if (user
->seq
< prb_first_valid_seq(prb
))
827 ret
= EPOLLIN
|EPOLLRDNORM
|EPOLLERR
|EPOLLPRI
;
829 ret
= EPOLLIN
|EPOLLRDNORM
;
836 static int devkmsg_open(struct inode
*inode
, struct file
*file
)
838 struct devkmsg_user
*user
;
841 if (devkmsg_log
& DEVKMSG_LOG_MASK_OFF
)
844 /* write-only does not need any file context */
845 if ((file
->f_flags
& O_ACCMODE
) != O_WRONLY
) {
846 err
= check_syslog_permissions(SYSLOG_ACTION_READ_ALL
,
852 user
= kmalloc(sizeof(struct devkmsg_user
), GFP_KERNEL
);
856 ratelimit_default_init(&user
->rs
);
857 ratelimit_set_flags(&user
->rs
, RATELIMIT_MSG_ON_RELEASE
);
859 mutex_init(&user
->lock
);
861 prb_rec_init_rd(&user
->record
, &user
->info
,
862 &user
->text_buf
[0], sizeof(user
->text_buf
));
865 user
->seq
= prb_first_valid_seq(prb
);
868 file
->private_data
= user
;
872 static int devkmsg_release(struct inode
*inode
, struct file
*file
)
874 struct devkmsg_user
*user
= file
->private_data
;
879 ratelimit_state_exit(&user
->rs
);
881 mutex_destroy(&user
->lock
);
886 const struct file_operations kmsg_fops
= {
887 .open
= devkmsg_open
,
888 .read
= devkmsg_read
,
889 .write_iter
= devkmsg_write
,
890 .llseek
= devkmsg_llseek
,
891 .poll
= devkmsg_poll
,
892 .release
= devkmsg_release
,
895 #ifdef CONFIG_CRASH_CORE
897 * This appends the listed symbols to /proc/vmcore
899 * /proc/vmcore is used by various utilities, like crash and makedumpfile to
900 * obtain access to symbols that are otherwise very difficult to locate. These
901 * symbols are specifically used so that utilities can access and extract the
902 * dmesg log from a vmcore file after a crash.
904 void log_buf_vmcoreinfo_setup(void)
906 struct dev_printk_info
*dev_info
= NULL
;
908 VMCOREINFO_SYMBOL(prb
);
909 VMCOREINFO_SYMBOL(printk_rb_static
);
910 VMCOREINFO_SYMBOL(clear_seq
);
913 * Export struct size and field offsets. User space tools can
914 * parse it and detect any changes to structure down the line.
917 VMCOREINFO_STRUCT_SIZE(printk_ringbuffer
);
918 VMCOREINFO_OFFSET(printk_ringbuffer
, desc_ring
);
919 VMCOREINFO_OFFSET(printk_ringbuffer
, text_data_ring
);
920 VMCOREINFO_OFFSET(printk_ringbuffer
, fail
);
922 VMCOREINFO_STRUCT_SIZE(prb_desc_ring
);
923 VMCOREINFO_OFFSET(prb_desc_ring
, count_bits
);
924 VMCOREINFO_OFFSET(prb_desc_ring
, descs
);
925 VMCOREINFO_OFFSET(prb_desc_ring
, infos
);
926 VMCOREINFO_OFFSET(prb_desc_ring
, head_id
);
927 VMCOREINFO_OFFSET(prb_desc_ring
, tail_id
);
929 VMCOREINFO_STRUCT_SIZE(prb_desc
);
930 VMCOREINFO_OFFSET(prb_desc
, state_var
);
931 VMCOREINFO_OFFSET(prb_desc
, text_blk_lpos
);
933 VMCOREINFO_STRUCT_SIZE(prb_data_blk_lpos
);
934 VMCOREINFO_OFFSET(prb_data_blk_lpos
, begin
);
935 VMCOREINFO_OFFSET(prb_data_blk_lpos
, next
);
937 VMCOREINFO_STRUCT_SIZE(printk_info
);
938 VMCOREINFO_OFFSET(printk_info
, seq
);
939 VMCOREINFO_OFFSET(printk_info
, ts_nsec
);
940 VMCOREINFO_OFFSET(printk_info
, text_len
);
941 VMCOREINFO_OFFSET(printk_info
, caller_id
);
942 VMCOREINFO_OFFSET(printk_info
, dev_info
);
944 VMCOREINFO_STRUCT_SIZE(dev_printk_info
);
945 VMCOREINFO_OFFSET(dev_printk_info
, subsystem
);
946 VMCOREINFO_LENGTH(printk_info_subsystem
, sizeof(dev_info
->subsystem
));
947 VMCOREINFO_OFFSET(dev_printk_info
, device
);
948 VMCOREINFO_LENGTH(printk_info_device
, sizeof(dev_info
->device
));
950 VMCOREINFO_STRUCT_SIZE(prb_data_ring
);
951 VMCOREINFO_OFFSET(prb_data_ring
, size_bits
);
952 VMCOREINFO_OFFSET(prb_data_ring
, data
);
953 VMCOREINFO_OFFSET(prb_data_ring
, head_lpos
);
954 VMCOREINFO_OFFSET(prb_data_ring
, tail_lpos
);
956 VMCOREINFO_SIZE(atomic_long_t
);
957 VMCOREINFO_TYPE_OFFSET(atomic_long_t
, counter
);
961 /* requested log_buf_len from kernel cmdline */
962 static unsigned long __initdata new_log_buf_len
;
964 /* we practice scaling the ring buffer by powers of 2 */
965 static void __init
log_buf_len_update(u64 size
)
967 if (size
> (u64
)LOG_BUF_LEN_MAX
) {
968 size
= (u64
)LOG_BUF_LEN_MAX
;
969 pr_err("log_buf over 2G is not supported.\n");
973 size
= roundup_pow_of_two(size
);
974 if (size
> log_buf_len
)
975 new_log_buf_len
= (unsigned long)size
;
978 /* save requested log_buf_len since it's too early to process it */
979 static int __init
log_buf_len_setup(char *str
)
986 size
= memparse(str
, &str
);
988 log_buf_len_update(size
);
992 early_param("log_buf_len", log_buf_len_setup
);
995 #define __LOG_CPU_MAX_BUF_LEN (1 << CONFIG_LOG_CPU_MAX_BUF_SHIFT)
997 static void __init
log_buf_add_cpu(void)
999 unsigned int cpu_extra
;
1002 * archs should set up cpu_possible_bits properly with
1003 * set_cpu_possible() after setup_arch() but just in
1004 * case lets ensure this is valid.
1006 if (num_possible_cpus() == 1)
1009 cpu_extra
= (num_possible_cpus() - 1) * __LOG_CPU_MAX_BUF_LEN
;
1011 /* by default this will only continue through for large > 64 CPUs */
1012 if (cpu_extra
<= __LOG_BUF_LEN
/ 2)
1015 pr_info("log_buf_len individual max cpu contribution: %d bytes\n",
1016 __LOG_CPU_MAX_BUF_LEN
);
1017 pr_info("log_buf_len total cpu_extra contributions: %d bytes\n",
1019 pr_info("log_buf_len min size: %d bytes\n", __LOG_BUF_LEN
);
1021 log_buf_len_update(cpu_extra
+ __LOG_BUF_LEN
);
1023 #else /* !CONFIG_SMP */
1024 static inline void log_buf_add_cpu(void) {}
1025 #endif /* CONFIG_SMP */
1027 static void __init
set_percpu_data_ready(void)
1030 /* Make sure we set this flag only after printk_safe() init is done */
1032 __printk_percpu_data_ready
= true;
1035 static unsigned int __init
add_to_rb(struct printk_ringbuffer
*rb
,
1036 struct printk_record
*r
)
1038 struct prb_reserved_entry e
;
1039 struct printk_record dest_r
;
1041 prb_rec_init_wr(&dest_r
, r
->info
->text_len
);
1043 if (!prb_reserve(&e
, rb
, &dest_r
))
1046 memcpy(&dest_r
.text_buf
[0], &r
->text_buf
[0], r
->info
->text_len
);
1047 dest_r
.info
->text_len
= r
->info
->text_len
;
1048 dest_r
.info
->facility
= r
->info
->facility
;
1049 dest_r
.info
->level
= r
->info
->level
;
1050 dest_r
.info
->flags
= r
->info
->flags
;
1051 dest_r
.info
->ts_nsec
= r
->info
->ts_nsec
;
1052 dest_r
.info
->caller_id
= r
->info
->caller_id
;
1053 memcpy(&dest_r
.info
->dev_info
, &r
->info
->dev_info
, sizeof(dest_r
.info
->dev_info
));
1055 prb_final_commit(&e
);
1057 return prb_record_text_space(&e
);
1060 static char setup_text_buf
[LOG_LINE_MAX
] __initdata
;
1062 void __init
setup_log_buf(int early
)
1064 struct printk_info
*new_infos
;
1065 unsigned int new_descs_count
;
1066 struct prb_desc
*new_descs
;
1067 struct printk_info info
;
1068 struct printk_record r
;
1069 size_t new_descs_size
;
1070 size_t new_infos_size
;
1071 unsigned long flags
;
1077 * Some archs call setup_log_buf() multiple times - first is very
1078 * early, e.g. from setup_arch(), and second - when percpu_areas
1082 set_percpu_data_ready();
1084 if (log_buf
!= __log_buf
)
1087 if (!early
&& !new_log_buf_len
)
1090 if (!new_log_buf_len
)
1093 new_descs_count
= new_log_buf_len
>> PRB_AVGBITS
;
1094 if (new_descs_count
== 0) {
1095 pr_err("new_log_buf_len: %lu too small\n", new_log_buf_len
);
1099 new_log_buf
= memblock_alloc(new_log_buf_len
, LOG_ALIGN
);
1100 if (unlikely(!new_log_buf
)) {
1101 pr_err("log_buf_len: %lu text bytes not available\n",
1106 new_descs_size
= new_descs_count
* sizeof(struct prb_desc
);
1107 new_descs
= memblock_alloc(new_descs_size
, LOG_ALIGN
);
1108 if (unlikely(!new_descs
)) {
1109 pr_err("log_buf_len: %zu desc bytes not available\n",
1111 goto err_free_log_buf
;
1114 new_infos_size
= new_descs_count
* sizeof(struct printk_info
);
1115 new_infos
= memblock_alloc(new_infos_size
, LOG_ALIGN
);
1116 if (unlikely(!new_infos
)) {
1117 pr_err("log_buf_len: %zu info bytes not available\n",
1119 goto err_free_descs
;
1122 prb_rec_init_rd(&r
, &info
, &setup_text_buf
[0], sizeof(setup_text_buf
));
1124 prb_init(&printk_rb_dynamic
,
1125 new_log_buf
, ilog2(new_log_buf_len
),
1126 new_descs
, ilog2(new_descs_count
),
1129 printk_safe_enter_irqsave(flags
);
1131 log_buf_len
= new_log_buf_len
;
1132 log_buf
= new_log_buf
;
1133 new_log_buf_len
= 0;
1135 free
= __LOG_BUF_LEN
;
1136 prb_for_each_record(0, &printk_rb_static
, seq
, &r
)
1137 free
-= add_to_rb(&printk_rb_dynamic
, &r
);
1140 * This is early enough that everything is still running on the
1141 * boot CPU and interrupts are disabled. So no new messages will
1142 * appear during the transition to the dynamic buffer.
1144 prb
= &printk_rb_dynamic
;
1146 printk_safe_exit_irqrestore(flags
);
1148 if (seq
!= prb_next_seq(&printk_rb_static
)) {
1149 pr_err("dropped %llu messages\n",
1150 prb_next_seq(&printk_rb_static
) - seq
);
1153 pr_info("log_buf_len: %u bytes\n", log_buf_len
);
1154 pr_info("early log buf free: %u(%u%%)\n",
1155 free
, (free
* 100) / __LOG_BUF_LEN
);
1159 memblock_free(__pa(new_descs
), new_descs_size
);
1161 memblock_free(__pa(new_log_buf
), new_log_buf_len
);
1164 static bool __read_mostly ignore_loglevel
;
1166 static int __init
ignore_loglevel_setup(char *str
)
1168 ignore_loglevel
= true;
1169 pr_info("debug: ignoring loglevel setting.\n");
1174 early_param("ignore_loglevel", ignore_loglevel_setup
);
1175 module_param(ignore_loglevel
, bool, S_IRUGO
| S_IWUSR
);
1176 MODULE_PARM_DESC(ignore_loglevel
,
1177 "ignore loglevel setting (prints all kernel messages to the console)");
1179 static bool suppress_message_printing(int level
)
1181 return (level
>= console_loglevel
&& !ignore_loglevel
);
1184 #ifdef CONFIG_BOOT_PRINTK_DELAY
1186 static int boot_delay
; /* msecs delay after each printk during bootup */
1187 static unsigned long long loops_per_msec
; /* based on boot_delay */
1189 static int __init
boot_delay_setup(char *str
)
1193 lpj
= preset_lpj
? preset_lpj
: 1000000; /* some guess */
1194 loops_per_msec
= (unsigned long long)lpj
/ 1000 * HZ
;
1196 get_option(&str
, &boot_delay
);
1197 if (boot_delay
> 10 * 1000)
1200 pr_debug("boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
1201 "HZ: %d, loops_per_msec: %llu\n",
1202 boot_delay
, preset_lpj
, lpj
, HZ
, loops_per_msec
);
1205 early_param("boot_delay", boot_delay_setup
);
1207 static void boot_delay_msec(int level
)
1209 unsigned long long k
;
1210 unsigned long timeout
;
1212 if ((boot_delay
== 0 || system_state
>= SYSTEM_RUNNING
)
1213 || suppress_message_printing(level
)) {
1217 k
= (unsigned long long)loops_per_msec
* boot_delay
;
1219 timeout
= jiffies
+ msecs_to_jiffies(boot_delay
);
1224 * use (volatile) jiffies to prevent
1225 * compiler reduction; loop termination via jiffies
1226 * is secondary and may or may not happen.
1228 if (time_after(jiffies
, timeout
))
1230 touch_nmi_watchdog();
1234 static inline void boot_delay_msec(int level
)
1239 static bool printk_time
= IS_ENABLED(CONFIG_PRINTK_TIME
);
1240 module_param_named(time
, printk_time
, bool, S_IRUGO
| S_IWUSR
);
1242 static size_t print_syslog(unsigned int level
, char *buf
)
1244 return sprintf(buf
, "<%u>", level
);
1247 static size_t print_time(u64 ts
, char *buf
)
1249 unsigned long rem_nsec
= do_div(ts
, 1000000000);
1251 return sprintf(buf
, "[%5lu.%06lu]",
1252 (unsigned long)ts
, rem_nsec
/ 1000);
1255 #ifdef CONFIG_PRINTK_CALLER
1256 static size_t print_caller(u32 id
, char *buf
)
1260 snprintf(caller
, sizeof(caller
), "%c%u",
1261 id
& 0x80000000 ? 'C' : 'T', id
& ~0x80000000);
1262 return sprintf(buf
, "[%6s]", caller
);
1265 #define print_caller(id, buf) 0
1268 static size_t info_print_prefix(const struct printk_info
*info
, bool syslog
,
1269 bool time
, char *buf
)
1274 len
= print_syslog((info
->facility
<< 3) | info
->level
, buf
);
1277 len
+= print_time(info
->ts_nsec
, buf
+ len
);
1279 len
+= print_caller(info
->caller_id
, buf
+ len
);
1281 if (IS_ENABLED(CONFIG_PRINTK_CALLER
) || time
) {
1290 * Prepare the record for printing. The text is shifted within the given
1291 * buffer to avoid a need for another one. The following operations are
1294 * - Add prefix for each line.
1295 * - Add the trailing newline that has been removed in vprintk_store().
1296 * - Drop truncated lines that do not longer fit into the buffer.
1298 * Return: The length of the updated/prepared text, including the added
1299 * prefixes and the newline. The dropped line(s) are not counted.
1301 static size_t record_print_text(struct printk_record
*r
, bool syslog
,
1304 size_t text_len
= r
->info
->text_len
;
1305 size_t buf_size
= r
->text_buf_size
;
1306 char *text
= r
->text_buf
;
1307 char prefix
[PREFIX_MAX
];
1308 bool truncated
= false;
1315 * If the message was truncated because the buffer was not large
1316 * enough, treat the available text as if it were the full text.
1318 if (text_len
> buf_size
)
1319 text_len
= buf_size
;
1321 prefix_len
= info_print_prefix(r
->info
, syslog
, time
, prefix
);
1324 * @text_len: bytes of unprocessed text
1325 * @line_len: bytes of current line _without_ newline
1326 * @text: pointer to beginning of current line
1327 * @len: number of bytes prepared in r->text_buf
1330 next
= memchr(text
, '\n', text_len
);
1332 line_len
= next
- text
;
1334 /* Drop truncated line(s). */
1337 line_len
= text_len
;
1341 * Truncate the text if there is not enough space to add the
1342 * prefix and a trailing newline.
1344 if (len
+ prefix_len
+ text_len
+ 1 > buf_size
) {
1345 /* Drop even the current line if no space. */
1346 if (len
+ prefix_len
+ line_len
+ 1 > buf_size
)
1349 text_len
= buf_size
- len
- prefix_len
- 1;
1353 memmove(text
+ prefix_len
, text
, text_len
);
1354 memcpy(text
, prefix
, prefix_len
);
1356 len
+= prefix_len
+ line_len
+ 1;
1358 if (text_len
== line_len
) {
1360 * Add the trailing newline removed in
1363 text
[prefix_len
+ line_len
] = '\n';
1368 * Advance beyond the added prefix and the related line with
1371 text
+= prefix_len
+ line_len
+ 1;
1374 * The remaining text has only decreased by the line with its
1377 * Note that @text_len can become zero. It happens when @text
1378 * ended with a newline (either due to truncation or the
1379 * original string ending with "\n\n"). The loop is correctly
1380 * repeated and (if not truncated) an empty line with a prefix
1383 text_len
-= line_len
+ 1;
1389 static size_t get_record_print_text_size(struct printk_info
*info
,
1390 unsigned int line_count
,
1391 bool syslog
, bool time
)
1393 char prefix
[PREFIX_MAX
];
1396 prefix_len
= info_print_prefix(info
, syslog
, time
, prefix
);
1399 * Each line will be preceded with a prefix. The intermediate
1400 * newlines are already within the text, but a final trailing
1401 * newline will be added.
1403 return ((prefix_len
* line_count
) + info
->text_len
+ 1);
1406 static int syslog_print(char __user
*buf
, int size
)
1408 struct printk_info info
;
1409 struct printk_record r
;
1413 text
= kmalloc(LOG_LINE_MAX
+ PREFIX_MAX
, GFP_KERNEL
);
1417 prb_rec_init_rd(&r
, &info
, text
, LOG_LINE_MAX
+ PREFIX_MAX
);
1424 if (!prb_read_valid(prb
, syslog_seq
, &r
)) {
1425 logbuf_unlock_irq();
1428 if (r
.info
->seq
!= syslog_seq
) {
1429 /* message is gone, move to next valid one */
1430 syslog_seq
= r
.info
->seq
;
1435 * To keep reading/counting partial line consistent,
1436 * use printk_time value as of the beginning of a line.
1438 if (!syslog_partial
)
1439 syslog_time
= printk_time
;
1441 skip
= syslog_partial
;
1442 n
= record_print_text(&r
, true, syslog_time
);
1443 if (n
- syslog_partial
<= size
) {
1444 /* message fits into buffer, move forward */
1445 syslog_seq
= r
.info
->seq
+ 1;
1446 n
-= syslog_partial
;
1449 /* partial read(), remember position */
1451 syslog_partial
+= n
;
1454 logbuf_unlock_irq();
1459 if (copy_to_user(buf
, text
+ skip
, n
)) {
1474 static int syslog_print_all(char __user
*buf
, int size
, bool clear
)
1476 struct printk_info info
;
1477 unsigned int line_count
;
1478 struct printk_record r
;
1484 text
= kmalloc(LOG_LINE_MAX
+ PREFIX_MAX
, GFP_KERNEL
);
1491 * Find first record that fits, including all following records,
1492 * into the user-provided buffer for this dump.
1494 prb_for_each_info(clear_seq
, prb
, seq
, &info
, &line_count
)
1495 len
+= get_record_print_text_size(&info
, line_count
, true, time
);
1497 /* move first record forward until length fits into the buffer */
1498 prb_for_each_info(clear_seq
, prb
, seq
, &info
, &line_count
) {
1501 len
-= get_record_print_text_size(&info
, line_count
, true, time
);
1504 prb_rec_init_rd(&r
, &info
, text
, LOG_LINE_MAX
+ PREFIX_MAX
);
1507 prb_for_each_record(seq
, prb
, seq
, &r
) {
1510 textlen
= record_print_text(&r
, true, time
);
1512 if (len
+ textlen
> size
) {
1517 logbuf_unlock_irq();
1518 if (copy_to_user(buf
+ len
, text
, textlen
))
1530 logbuf_unlock_irq();
1536 static void syslog_clear(void)
1539 clear_seq
= prb_next_seq(prb
);
1540 logbuf_unlock_irq();
1543 int do_syslog(int type
, char __user
*buf
, int len
, int source
)
1546 static int saved_console_loglevel
= LOGLEVEL_DEFAULT
;
1549 error
= check_syslog_permissions(type
, source
);
1554 case SYSLOG_ACTION_CLOSE
: /* Close log */
1556 case SYSLOG_ACTION_OPEN
: /* Open log */
1558 case SYSLOG_ACTION_READ
: /* Read from log */
1559 if (!buf
|| len
< 0)
1563 if (!access_ok(buf
, len
))
1565 error
= wait_event_interruptible(log_wait
,
1566 prb_read_valid(prb
, syslog_seq
, NULL
));
1569 error
= syslog_print(buf
, len
);
1571 /* Read/clear last kernel messages */
1572 case SYSLOG_ACTION_READ_CLEAR
:
1575 /* Read last kernel messages */
1576 case SYSLOG_ACTION_READ_ALL
:
1577 if (!buf
|| len
< 0)
1581 if (!access_ok(buf
, len
))
1583 error
= syslog_print_all(buf
, len
, clear
);
1585 /* Clear ring buffer */
1586 case SYSLOG_ACTION_CLEAR
:
1589 /* Disable logging to console */
1590 case SYSLOG_ACTION_CONSOLE_OFF
:
1591 if (saved_console_loglevel
== LOGLEVEL_DEFAULT
)
1592 saved_console_loglevel
= console_loglevel
;
1593 console_loglevel
= minimum_console_loglevel
;
1595 /* Enable logging to console */
1596 case SYSLOG_ACTION_CONSOLE_ON
:
1597 if (saved_console_loglevel
!= LOGLEVEL_DEFAULT
) {
1598 console_loglevel
= saved_console_loglevel
;
1599 saved_console_loglevel
= LOGLEVEL_DEFAULT
;
1602 /* Set level of messages printed to console */
1603 case SYSLOG_ACTION_CONSOLE_LEVEL
:
1604 if (len
< 1 || len
> 8)
1606 if (len
< minimum_console_loglevel
)
1607 len
= minimum_console_loglevel
;
1608 console_loglevel
= len
;
1609 /* Implicitly re-enable logging to console */
1610 saved_console_loglevel
= LOGLEVEL_DEFAULT
;
1612 /* Number of chars in the log buffer */
1613 case SYSLOG_ACTION_SIZE_UNREAD
:
1615 if (syslog_seq
< prb_first_valid_seq(prb
)) {
1616 /* messages are gone, move to first one */
1617 syslog_seq
= prb_first_valid_seq(prb
);
1620 if (source
== SYSLOG_FROM_PROC
) {
1622 * Short-cut for poll(/"proc/kmsg") which simply checks
1623 * for pending data, not the size; return the count of
1624 * records, not the length.
1626 error
= prb_next_seq(prb
) - syslog_seq
;
1628 bool time
= syslog_partial
? syslog_time
: printk_time
;
1629 struct printk_info info
;
1630 unsigned int line_count
;
1633 prb_for_each_info(syslog_seq
, prb
, seq
, &info
,
1635 error
+= get_record_print_text_size(&info
, line_count
,
1639 error
-= syslog_partial
;
1641 logbuf_unlock_irq();
1643 /* Size of the log buffer */
1644 case SYSLOG_ACTION_SIZE_BUFFER
:
1645 error
= log_buf_len
;
1655 SYSCALL_DEFINE3(syslog
, int, type
, char __user
*, buf
, int, len
)
1657 return do_syslog(type
, buf
, len
, SYSLOG_FROM_READER
);
1661 * Special console_lock variants that help to reduce the risk of soft-lockups.
1662 * They allow to pass console_lock to another printk() call using a busy wait.
1665 #ifdef CONFIG_LOCKDEP
1666 static struct lockdep_map console_owner_dep_map
= {
1667 .name
= "console_owner"
1671 static DEFINE_RAW_SPINLOCK(console_owner_lock
);
1672 static struct task_struct
*console_owner
;
1673 static bool console_waiter
;
1676 * console_lock_spinning_enable - mark beginning of code where another
1677 * thread might safely busy wait
1679 * This basically converts console_lock into a spinlock. This marks
1680 * the section where the console_lock owner can not sleep, because
1681 * there may be a waiter spinning (like a spinlock). Also it must be
1682 * ready to hand over the lock at the end of the section.
1684 static void console_lock_spinning_enable(void)
1686 raw_spin_lock(&console_owner_lock
);
1687 console_owner
= current
;
1688 raw_spin_unlock(&console_owner_lock
);
1690 /* The waiter may spin on us after setting console_owner */
1691 spin_acquire(&console_owner_dep_map
, 0, 0, _THIS_IP_
);
1695 * console_lock_spinning_disable_and_check - mark end of code where another
1696 * thread was able to busy wait and check if there is a waiter
1698 * This is called at the end of the section where spinning is allowed.
1699 * It has two functions. First, it is a signal that it is no longer
1700 * safe to start busy waiting for the lock. Second, it checks if
1701 * there is a busy waiter and passes the lock rights to her.
1703 * Important: Callers lose the lock if there was a busy waiter.
1704 * They must not touch items synchronized by console_lock
1707 * Return: 1 if the lock rights were passed, 0 otherwise.
1709 static int console_lock_spinning_disable_and_check(void)
1713 raw_spin_lock(&console_owner_lock
);
1714 waiter
= READ_ONCE(console_waiter
);
1715 console_owner
= NULL
;
1716 raw_spin_unlock(&console_owner_lock
);
1719 spin_release(&console_owner_dep_map
, _THIS_IP_
);
1723 /* The waiter is now free to continue */
1724 WRITE_ONCE(console_waiter
, false);
1726 spin_release(&console_owner_dep_map
, _THIS_IP_
);
1729 * Hand off console_lock to waiter. The waiter will perform
1730 * the up(). After this, the waiter is the console_lock owner.
1732 mutex_release(&console_lock_dep_map
, _THIS_IP_
);
1737 * console_trylock_spinning - try to get console_lock by busy waiting
1739 * This allows to busy wait for the console_lock when the current
1740 * owner is running in specially marked sections. It means that
1741 * the current owner is running and cannot reschedule until it
1742 * is ready to lose the lock.
1744 * Return: 1 if we got the lock, 0 othrewise
1746 static int console_trylock_spinning(void)
1748 struct task_struct
*owner
= NULL
;
1751 unsigned long flags
;
1753 if (console_trylock())
1756 printk_safe_enter_irqsave(flags
);
1758 raw_spin_lock(&console_owner_lock
);
1759 owner
= READ_ONCE(console_owner
);
1760 waiter
= READ_ONCE(console_waiter
);
1761 if (!waiter
&& owner
&& owner
!= current
) {
1762 WRITE_ONCE(console_waiter
, true);
1765 raw_spin_unlock(&console_owner_lock
);
1768 * If there is an active printk() writing to the
1769 * consoles, instead of having it write our data too,
1770 * see if we can offload that load from the active
1771 * printer, and do some printing ourselves.
1772 * Go into a spin only if there isn't already a waiter
1773 * spinning, and there is an active printer, and
1774 * that active printer isn't us (recursive printk?).
1777 printk_safe_exit_irqrestore(flags
);
1781 /* We spin waiting for the owner to release us */
1782 spin_acquire(&console_owner_dep_map
, 0, 0, _THIS_IP_
);
1783 /* Owner will clear console_waiter on hand off */
1784 while (READ_ONCE(console_waiter
))
1786 spin_release(&console_owner_dep_map
, _THIS_IP_
);
1788 printk_safe_exit_irqrestore(flags
);
1790 * The owner passed the console lock to us.
1791 * Since we did not spin on console lock, annotate
1792 * this as a trylock. Otherwise lockdep will
1795 mutex_acquire(&console_lock_dep_map
, 0, 1, _THIS_IP_
);
1801 * Call the console drivers, asking them to write out
1802 * log_buf[start] to log_buf[end - 1].
1803 * The console_lock must be held.
1805 static void call_console_drivers(const char *ext_text
, size_t ext_len
,
1806 const char *text
, size_t len
)
1808 static char dropped_text
[64];
1809 size_t dropped_len
= 0;
1810 struct console
*con
;
1812 trace_console_rcuidle(text
, len
);
1814 if (!console_drivers
)
1817 if (console_dropped
) {
1818 dropped_len
= snprintf(dropped_text
, sizeof(dropped_text
),
1819 "** %lu printk messages dropped **\n",
1821 console_dropped
= 0;
1824 for_each_console(con
) {
1825 if (exclusive_console
&& con
!= exclusive_console
)
1827 if (!(con
->flags
& CON_ENABLED
))
1831 if (!cpu_online(smp_processor_id()) &&
1832 !(con
->flags
& CON_ANYTIME
))
1834 if (con
->flags
& CON_EXTENDED
)
1835 con
->write(con
, ext_text
, ext_len
);
1838 con
->write(con
, dropped_text
, dropped_len
);
1839 con
->write(con
, text
, len
);
1844 int printk_delay_msec __read_mostly
;
1846 static inline void printk_delay(void)
1848 if (unlikely(printk_delay_msec
)) {
1849 int m
= printk_delay_msec
;
1853 touch_nmi_watchdog();
1858 static inline u32
printk_caller_id(void)
1860 return in_task() ? task_pid_nr(current
) :
1861 0x80000000 + raw_smp_processor_id();
1865 * parse_prefix - Parse level and control flags.
1867 * @text: The terminated text message.
1868 * @level: A pointer to the current level value, will be updated.
1869 * @lflags: A pointer to the current log flags, will be updated.
1871 * @level may be NULL if the caller is not interested in the parsed value.
1872 * Otherwise the variable pointed to by @level must be set to
1873 * LOGLEVEL_DEFAULT in order to be updated with the parsed value.
1875 * @lflags may be NULL if the caller is not interested in the parsed value.
1876 * Otherwise the variable pointed to by @lflags will be OR'd with the parsed
1879 * Return: The length of the parsed level and control flags.
1881 static u16
parse_prefix(char *text
, int *level
, enum log_flags
*lflags
)
1887 kern_level
= printk_get_level(text
);
1891 switch (kern_level
) {
1893 if (level
&& *level
== LOGLEVEL_DEFAULT
)
1894 *level
= kern_level
- '0';
1896 case 'c': /* KERN_CONT */
1898 *lflags
|= LOG_CONT
;
1908 static u16
printk_sprint(char *text
, u16 size
, int facility
, enum log_flags
*lflags
,
1909 const char *fmt
, va_list args
)
1913 text_len
= vscnprintf(text
, size
, fmt
, args
);
1915 /* Mark and strip a trailing newline. */
1916 if (text_len
&& text
[text_len
- 1] == '\n') {
1918 *lflags
|= LOG_NEWLINE
;
1921 /* Strip log level and control flags. */
1922 if (facility
== 0) {
1925 prefix_len
= parse_prefix(text
, NULL
, NULL
);
1927 text_len
-= prefix_len
;
1928 memmove(text
, text
+ prefix_len
, text_len
);
1936 int vprintk_store(int facility
, int level
,
1937 const struct dev_printk_info
*dev_info
,
1938 const char *fmt
, va_list args
)
1940 const u32 caller_id
= printk_caller_id();
1941 struct prb_reserved_entry e
;
1942 enum log_flags lflags
= 0;
1943 struct printk_record r
;
1944 u16 trunc_msg_len
= 0;
1952 * Since the duration of printk() can vary depending on the message
1953 * and state of the ringbuffer, grab the timestamp now so that it is
1954 * close to the call of printk(). This provides a more deterministic
1955 * timestamp with respect to the caller.
1957 ts_nsec
= local_clock();
1960 * The sprintf needs to come first since the syslog prefix might be
1961 * passed in as a parameter. An extra byte must be reserved so that
1962 * later the vscnprintf() into the reserved buffer has room for the
1963 * terminating '\0', which is not counted by vsnprintf().
1965 va_copy(args2
, args
);
1966 reserve_size
= vsnprintf(&prefix_buf
[0], sizeof(prefix_buf
), fmt
, args2
) + 1;
1969 if (reserve_size
> LOG_LINE_MAX
)
1970 reserve_size
= LOG_LINE_MAX
;
1972 /* Extract log level or control flags. */
1974 parse_prefix(&prefix_buf
[0], &level
, &lflags
);
1976 if (level
== LOGLEVEL_DEFAULT
)
1977 level
= default_message_loglevel
;
1980 lflags
|= LOG_NEWLINE
;
1982 if (lflags
& LOG_CONT
) {
1983 prb_rec_init_wr(&r
, reserve_size
);
1984 if (prb_reserve_in_last(&e
, prb
, &r
, caller_id
, LOG_LINE_MAX
)) {
1985 text_len
= printk_sprint(&r
.text_buf
[r
.info
->text_len
], reserve_size
,
1986 facility
, &lflags
, fmt
, args
);
1987 r
.info
->text_len
+= text_len
;
1989 if (lflags
& LOG_NEWLINE
) {
1990 r
.info
->flags
|= LOG_NEWLINE
;
1991 prb_final_commit(&e
);
2001 * Explicitly initialize the record before every prb_reserve() call.
2002 * prb_reserve_in_last() and prb_reserve() purposely invalidate the
2003 * structure when they fail.
2005 prb_rec_init_wr(&r
, reserve_size
);
2006 if (!prb_reserve(&e
, prb
, &r
)) {
2007 /* truncate the message if it is too long for empty buffer */
2008 truncate_msg(&reserve_size
, &trunc_msg_len
);
2010 prb_rec_init_wr(&r
, reserve_size
+ trunc_msg_len
);
2011 if (!prb_reserve(&e
, prb
, &r
))
2016 text_len
= printk_sprint(&r
.text_buf
[0], reserve_size
, facility
, &lflags
, fmt
, args
);
2018 memcpy(&r
.text_buf
[text_len
], trunc_msg
, trunc_msg_len
);
2019 r
.info
->text_len
= text_len
+ trunc_msg_len
;
2020 r
.info
->facility
= facility
;
2021 r
.info
->level
= level
& 7;
2022 r
.info
->flags
= lflags
& 0x1f;
2023 r
.info
->ts_nsec
= ts_nsec
;
2024 r
.info
->caller_id
= caller_id
;
2026 memcpy(&r
.info
->dev_info
, dev_info
, sizeof(r
.info
->dev_info
));
2028 /* A message without a trailing newline can be continued. */
2029 if (!(lflags
& LOG_NEWLINE
))
2032 prb_final_commit(&e
);
2034 return (text_len
+ trunc_msg_len
);
2037 asmlinkage
int vprintk_emit(int facility
, int level
,
2038 const struct dev_printk_info
*dev_info
,
2039 const char *fmt
, va_list args
)
2042 bool in_sched
= false;
2043 unsigned long flags
;
2045 /* Suppress unimportant messages after panic happens */
2046 if (unlikely(suppress_printk
))
2049 if (level
== LOGLEVEL_SCHED
) {
2050 level
= LOGLEVEL_DEFAULT
;
2054 boot_delay_msec(level
);
2057 printk_safe_enter_irqsave(flags
);
2058 printed_len
= vprintk_store(facility
, level
, dev_info
, fmt
, args
);
2059 printk_safe_exit_irqrestore(flags
);
2061 /* If called from the scheduler, we can not call up(). */
2064 * Disable preemption to avoid being preempted while holding
2065 * console_sem which would prevent anyone from printing to
2070 * Try to acquire and then immediately release the console
2071 * semaphore. The release will print out buffers and wake up
2072 * /dev/kmsg and syslog() users.
2074 if (console_trylock_spinning())
2082 EXPORT_SYMBOL(vprintk_emit
);
2084 asmlinkage
int vprintk(const char *fmt
, va_list args
)
2086 return vprintk_func(fmt
, args
);
2088 EXPORT_SYMBOL(vprintk
);
2090 int vprintk_default(const char *fmt
, va_list args
)
2092 return vprintk_emit(0, LOGLEVEL_DEFAULT
, NULL
, fmt
, args
);
2094 EXPORT_SYMBOL_GPL(vprintk_default
);
2097 * printk - print a kernel message
2098 * @fmt: format string
2100 * This is printk(). It can be called from any context. We want it to work.
2102 * We try to grab the console_lock. If we succeed, it's easy - we log the
2103 * output and call the console drivers. If we fail to get the semaphore, we
2104 * place the output into the log buffer and return. The current holder of
2105 * the console_sem will notice the new output in console_unlock(); and will
2106 * send it to the consoles before releasing the lock.
2108 * One effect of this deferred printing is that code which calls printk() and
2109 * then changes console_loglevel may break. This is because console_loglevel
2110 * is inspected when the actual printing occurs.
2115 * See the vsnprintf() documentation for format string extensions over C99.
2117 asmlinkage __visible
int printk(const char *fmt
, ...)
2122 va_start(args
, fmt
);
2123 r
= vprintk_func(fmt
, args
);
2128 EXPORT_SYMBOL(printk
);
2130 #else /* CONFIG_PRINTK */
2132 #define LOG_LINE_MAX 0
2133 #define PREFIX_MAX 0
2134 #define printk_time false
2136 #define prb_read_valid(rb, seq, r) false
2137 #define prb_first_valid_seq(rb) 0
2139 static u64 syslog_seq
;
2140 static u64 console_seq
;
2141 static u64 exclusive_console_stop_seq
;
2142 static unsigned long console_dropped
;
2144 static size_t record_print_text(const struct printk_record
*r
,
2145 bool syslog
, bool time
)
2149 static ssize_t
info_print_ext_header(char *buf
, size_t size
,
2150 struct printk_info
*info
)
2154 static ssize_t
msg_print_ext_body(char *buf
, size_t size
,
2155 char *text
, size_t text_len
,
2156 struct dev_printk_info
*dev_info
) { return 0; }
2157 static void console_lock_spinning_enable(void) { }
2158 static int console_lock_spinning_disable_and_check(void) { return 0; }
2159 static void call_console_drivers(const char *ext_text
, size_t ext_len
,
2160 const char *text
, size_t len
) {}
2161 static bool suppress_message_printing(int level
) { return false; }
2163 #endif /* CONFIG_PRINTK */
2165 #ifdef CONFIG_EARLY_PRINTK
2166 struct console
*early_console
;
2168 asmlinkage __visible
void early_printk(const char *fmt
, ...)
2178 n
= vscnprintf(buf
, sizeof(buf
), fmt
, ap
);
2181 early_console
->write(early_console
, buf
, n
);
2185 static int __add_preferred_console(char *name
, int idx
, char *options
,
2186 char *brl_options
, bool user_specified
)
2188 struct console_cmdline
*c
;
2192 * See if this tty is not yet registered, and
2193 * if we have a slot free.
2195 for (i
= 0, c
= console_cmdline
;
2196 i
< MAX_CMDLINECONSOLES
&& c
->name
[0];
2198 if (strcmp(c
->name
, name
) == 0 && c
->index
== idx
) {
2200 preferred_console
= i
;
2202 c
->user_specified
= true;
2206 if (i
== MAX_CMDLINECONSOLES
)
2209 preferred_console
= i
;
2210 strlcpy(c
->name
, name
, sizeof(c
->name
));
2211 c
->options
= options
;
2212 c
->user_specified
= user_specified
;
2213 braille_set_options(c
, brl_options
);
2219 static int __init
console_msg_format_setup(char *str
)
2221 if (!strcmp(str
, "syslog"))
2222 console_msg_format
= MSG_FORMAT_SYSLOG
;
2223 if (!strcmp(str
, "default"))
2224 console_msg_format
= MSG_FORMAT_DEFAULT
;
2227 __setup("console_msg_format=", console_msg_format_setup
);
2230 * Set up a console. Called via do_early_param() in init/main.c
2231 * for each "console=" parameter in the boot command line.
2233 static int __init
console_setup(char *str
)
2235 char buf
[sizeof(console_cmdline
[0].name
) + 4]; /* 4 for "ttyS" */
2236 char *s
, *options
, *brl_options
= NULL
;
2240 * console="" or console=null have been suggested as a way to
2241 * disable console output. Use ttynull that has been created
2242 * for exacly this purpose.
2244 if (str
[0] == 0 || strcmp(str
, "null") == 0) {
2245 __add_preferred_console("ttynull", 0, NULL
, NULL
, true);
2249 if (_braille_console_setup(&str
, &brl_options
))
2253 * Decode str into name, index, options.
2255 if (str
[0] >= '0' && str
[0] <= '9') {
2256 strcpy(buf
, "ttyS");
2257 strncpy(buf
+ 4, str
, sizeof(buf
) - 5);
2259 strncpy(buf
, str
, sizeof(buf
) - 1);
2261 buf
[sizeof(buf
) - 1] = 0;
2262 options
= strchr(str
, ',');
2266 if (!strcmp(str
, "ttya"))
2267 strcpy(buf
, "ttyS0");
2268 if (!strcmp(str
, "ttyb"))
2269 strcpy(buf
, "ttyS1");
2271 for (s
= buf
; *s
; s
++)
2272 if (isdigit(*s
) || *s
== ',')
2274 idx
= simple_strtoul(s
, NULL
, 10);
2277 __add_preferred_console(buf
, idx
, options
, brl_options
, true);
2278 console_set_on_cmdline
= 1;
2281 __setup("console=", console_setup
);
2284 * add_preferred_console - add a device to the list of preferred consoles.
2285 * @name: device name
2286 * @idx: device index
2287 * @options: options for this console
2289 * The last preferred console added will be used for kernel messages
2290 * and stdin/out/err for init. Normally this is used by console_setup
2291 * above to handle user-supplied console arguments; however it can also
2292 * be used by arch-specific code either to override the user or more
2293 * commonly to provide a default console (ie from PROM variables) when
2294 * the user has not supplied one.
2296 int add_preferred_console(char *name
, int idx
, char *options
)
2298 return __add_preferred_console(name
, idx
, options
, NULL
, false);
2301 bool console_suspend_enabled
= true;
2302 EXPORT_SYMBOL(console_suspend_enabled
);
2304 static int __init
console_suspend_disable(char *str
)
2306 console_suspend_enabled
= false;
2309 __setup("no_console_suspend", console_suspend_disable
);
2310 module_param_named(console_suspend
, console_suspend_enabled
,
2311 bool, S_IRUGO
| S_IWUSR
);
2312 MODULE_PARM_DESC(console_suspend
, "suspend console during suspend"
2313 " and hibernate operations");
2316 * suspend_console - suspend the console subsystem
2318 * This disables printk() while we go into suspend states
2320 void suspend_console(void)
2322 if (!console_suspend_enabled
)
2324 pr_info("Suspending console(s) (use no_console_suspend to debug)\n");
2326 console_suspended
= 1;
2330 void resume_console(void)
2332 if (!console_suspend_enabled
)
2335 console_suspended
= 0;
2340 * console_cpu_notify - print deferred console messages after CPU hotplug
2343 * If printk() is called from a CPU that is not online yet, the messages
2344 * will be printed on the console only if there are CON_ANYTIME consoles.
2345 * This function is called when a new CPU comes online (or fails to come
2346 * up) or goes offline.
2348 static int console_cpu_notify(unsigned int cpu
)
2350 if (!cpuhp_tasks_frozen
) {
2351 /* If trylock fails, someone else is doing the printing */
2352 if (console_trylock())
2359 * console_lock - lock the console system for exclusive use.
2361 * Acquires a lock which guarantees that the caller has
2362 * exclusive access to the console system and the console_drivers list.
2364 * Can sleep, returns nothing.
2366 void console_lock(void)
2371 if (console_suspended
)
2374 console_may_schedule
= 1;
2376 EXPORT_SYMBOL(console_lock
);
2379 * console_trylock - try to lock the console system for exclusive use.
2381 * Try to acquire a lock which guarantees that the caller has exclusive
2382 * access to the console system and the console_drivers list.
2384 * returns 1 on success, and 0 on failure to acquire the lock.
2386 int console_trylock(void)
2388 if (down_trylock_console_sem())
2390 if (console_suspended
) {
2395 console_may_schedule
= 0;
2398 EXPORT_SYMBOL(console_trylock
);
2400 int is_console_locked(void)
2402 return console_locked
;
2404 EXPORT_SYMBOL(is_console_locked
);
2407 * Check if we have any console that is capable of printing while cpu is
2408 * booting or shutting down. Requires console_sem.
2410 static int have_callable_console(void)
2412 struct console
*con
;
2414 for_each_console(con
)
2415 if ((con
->flags
& CON_ENABLED
) &&
2416 (con
->flags
& CON_ANYTIME
))
2423 * Can we actually use the console at this time on this cpu?
2425 * Console drivers may assume that per-cpu resources have been allocated. So
2426 * unless they're explicitly marked as being able to cope (CON_ANYTIME) don't
2427 * call them until this CPU is officially up.
2429 static inline int can_use_console(void)
2431 return cpu_online(raw_smp_processor_id()) || have_callable_console();
2435 * console_unlock - unlock the console system
2437 * Releases the console_lock which the caller holds on the console system
2438 * and the console driver list.
2440 * While the console_lock was held, console output may have been buffered
2441 * by printk(). If this is the case, console_unlock(); emits
2442 * the output prior to releasing the lock.
2444 * If there is output waiting, we wake /dev/kmsg and syslog() users.
2446 * console_unlock(); may be called from any context.
2448 void console_unlock(void)
2450 static char ext_text
[CONSOLE_EXT_LOG_MAX
];
2451 static char text
[LOG_LINE_MAX
+ PREFIX_MAX
];
2452 unsigned long flags
;
2453 bool do_cond_resched
, retry
;
2454 struct printk_info info
;
2455 struct printk_record r
;
2457 if (console_suspended
) {
2462 prb_rec_init_rd(&r
, &info
, text
, sizeof(text
));
2465 * Console drivers are called with interrupts disabled, so
2466 * @console_may_schedule should be cleared before; however, we may
2467 * end up dumping a lot of lines, for example, if called from
2468 * console registration path, and should invoke cond_resched()
2469 * between lines if allowable. Not doing so can cause a very long
2470 * scheduling stall on a slow console leading to RCU stall and
2471 * softlockup warnings which exacerbate the issue with more
2472 * messages practically incapacitating the system.
2474 * console_trylock() is not able to detect the preemptive
2475 * context reliably. Therefore the value must be stored before
2476 * and cleared after the "again" goto label.
2478 do_cond_resched
= console_may_schedule
;
2480 console_may_schedule
= 0;
2483 * We released the console_sem lock, so we need to recheck if
2484 * cpu is online and (if not) is there at least one CON_ANYTIME
2487 if (!can_use_console()) {
2497 printk_safe_enter_irqsave(flags
);
2498 raw_spin_lock(&logbuf_lock
);
2500 if (!prb_read_valid(prb
, console_seq
, &r
))
2503 if (console_seq
!= r
.info
->seq
) {
2504 console_dropped
+= r
.info
->seq
- console_seq
;
2505 console_seq
= r
.info
->seq
;
2508 if (suppress_message_printing(r
.info
->level
)) {
2510 * Skip record we have buffered and already printed
2511 * directly to the console when we received it, and
2512 * record that has level above the console loglevel.
2518 /* Output to all consoles once old messages replayed. */
2519 if (unlikely(exclusive_console
&&
2520 console_seq
>= exclusive_console_stop_seq
)) {
2521 exclusive_console
= NULL
;
2525 * Handle extended console text first because later
2526 * record_print_text() will modify the record buffer in-place.
2528 if (nr_ext_console_drivers
) {
2529 ext_len
= info_print_ext_header(ext_text
,
2532 ext_len
+= msg_print_ext_body(ext_text
+ ext_len
,
2533 sizeof(ext_text
) - ext_len
,
2538 len
= record_print_text(&r
,
2539 console_msg_format
& MSG_FORMAT_SYSLOG
,
2542 raw_spin_unlock(&logbuf_lock
);
2545 * While actively printing out messages, if another printk()
2546 * were to occur on another CPU, it may wait for this one to
2547 * finish. This task can not be preempted if there is a
2548 * waiter waiting to take over.
2550 console_lock_spinning_enable();
2552 stop_critical_timings(); /* don't trace print latency */
2553 call_console_drivers(ext_text
, ext_len
, text
, len
);
2554 start_critical_timings();
2556 if (console_lock_spinning_disable_and_check()) {
2557 printk_safe_exit_irqrestore(flags
);
2561 printk_safe_exit_irqrestore(flags
);
2563 if (do_cond_resched
)
2569 raw_spin_unlock(&logbuf_lock
);
2574 * Someone could have filled up the buffer again, so re-check if there's
2575 * something to flush. In case we cannot trylock the console_sem again,
2576 * there's a new owner and the console_unlock() from them will do the
2577 * flush, no worries.
2579 raw_spin_lock(&logbuf_lock
);
2580 retry
= prb_read_valid(prb
, console_seq
, NULL
);
2581 raw_spin_unlock(&logbuf_lock
);
2582 printk_safe_exit_irqrestore(flags
);
2584 if (retry
&& console_trylock())
2587 EXPORT_SYMBOL(console_unlock
);
2590 * console_conditional_schedule - yield the CPU if required
2592 * If the console code is currently allowed to sleep, and
2593 * if this CPU should yield the CPU to another task, do
2596 * Must be called within console_lock();.
2598 void __sched
console_conditional_schedule(void)
2600 if (console_may_schedule
)
2603 EXPORT_SYMBOL(console_conditional_schedule
);
2605 void console_unblank(void)
2610 * console_unblank can no longer be called in interrupt context unless
2611 * oops_in_progress is set to 1..
2613 if (oops_in_progress
) {
2614 if (down_trylock_console_sem() != 0)
2620 console_may_schedule
= 0;
2622 if ((c
->flags
& CON_ENABLED
) && c
->unblank
)
2628 * console_flush_on_panic - flush console content on panic
2629 * @mode: flush all messages in buffer or just the pending ones
2631 * Immediately output all pending messages no matter what.
2633 void console_flush_on_panic(enum con_flush_mode mode
)
2636 * If someone else is holding the console lock, trylock will fail
2637 * and may_schedule may be set. Ignore and proceed to unlock so
2638 * that messages are flushed out. As this can be called from any
2639 * context and we don't want to get preempted while flushing,
2640 * ensure may_schedule is cleared.
2643 console_may_schedule
= 0;
2645 if (mode
== CONSOLE_REPLAY_ALL
) {
2646 unsigned long flags
;
2648 logbuf_lock_irqsave(flags
);
2649 console_seq
= prb_first_valid_seq(prb
);
2650 logbuf_unlock_irqrestore(flags
);
2656 * Return the console tty driver structure and its associated index
2658 struct tty_driver
*console_device(int *index
)
2661 struct tty_driver
*driver
= NULL
;
2664 for_each_console(c
) {
2667 driver
= c
->device(c
, index
);
2676 * Prevent further output on the passed console device so that (for example)
2677 * serial drivers can disable console output before suspending a port, and can
2678 * re-enable output afterwards.
2680 void console_stop(struct console
*console
)
2683 console
->flags
&= ~CON_ENABLED
;
2686 EXPORT_SYMBOL(console_stop
);
2688 void console_start(struct console
*console
)
2691 console
->flags
|= CON_ENABLED
;
2694 EXPORT_SYMBOL(console_start
);
2696 static int __read_mostly keep_bootcon
;
2698 static int __init
keep_bootcon_setup(char *str
)
2701 pr_info("debug: skip boot console de-registration.\n");
2706 early_param("keep_bootcon", keep_bootcon_setup
);
2709 * This is called by register_console() to try to match
2710 * the newly registered console with any of the ones selected
2711 * by either the command line or add_preferred_console() and
2714 * Care need to be taken with consoles that are statically
2715 * enabled such as netconsole
2717 static int try_enable_new_console(struct console
*newcon
, bool user_specified
)
2719 struct console_cmdline
*c
;
2722 for (i
= 0, c
= console_cmdline
;
2723 i
< MAX_CMDLINECONSOLES
&& c
->name
[0];
2725 if (c
->user_specified
!= user_specified
)
2727 if (!newcon
->match
||
2728 newcon
->match(newcon
, c
->name
, c
->index
, c
->options
) != 0) {
2729 /* default matching */
2730 BUILD_BUG_ON(sizeof(c
->name
) != sizeof(newcon
->name
));
2731 if (strcmp(c
->name
, newcon
->name
) != 0)
2733 if (newcon
->index
>= 0 &&
2734 newcon
->index
!= c
->index
)
2736 if (newcon
->index
< 0)
2737 newcon
->index
= c
->index
;
2739 if (_braille_register_console(newcon
, c
))
2742 if (newcon
->setup
&&
2743 (err
= newcon
->setup(newcon
, c
->options
)) != 0)
2746 newcon
->flags
|= CON_ENABLED
;
2747 if (i
== preferred_console
) {
2748 newcon
->flags
|= CON_CONSDEV
;
2749 has_preferred_console
= true;
2755 * Some consoles, such as pstore and netconsole, can be enabled even
2756 * without matching. Accept the pre-enabled consoles only when match()
2757 * and setup() had a chance to be called.
2759 if (newcon
->flags
& CON_ENABLED
&& c
->user_specified
== user_specified
)
2766 * The console driver calls this routine during kernel initialization
2767 * to register the console printing procedure with printk() and to
2768 * print any messages that were printed by the kernel before the
2769 * console driver was initialized.
2771 * This can happen pretty early during the boot process (because of
2772 * early_printk) - sometimes before setup_arch() completes - be careful
2773 * of what kernel features are used - they may not be initialised yet.
2775 * There are two types of consoles - bootconsoles (early_printk) and
2776 * "real" consoles (everything which is not a bootconsole) which are
2777 * handled differently.
2778 * - Any number of bootconsoles can be registered at any time.
2779 * - As soon as a "real" console is registered, all bootconsoles
2780 * will be unregistered automatically.
2781 * - Once a "real" console is registered, any attempt to register a
2782 * bootconsoles will be rejected
2784 void register_console(struct console
*newcon
)
2786 unsigned long flags
;
2787 struct console
*bcon
= NULL
;
2790 for_each_console(bcon
) {
2791 if (WARN(bcon
== newcon
, "console '%s%d' already registered\n",
2792 bcon
->name
, bcon
->index
))
2797 * before we register a new CON_BOOT console, make sure we don't
2798 * already have a valid console
2800 if (newcon
->flags
& CON_BOOT
) {
2801 for_each_console(bcon
) {
2802 if (!(bcon
->flags
& CON_BOOT
)) {
2803 pr_info("Too late to register bootconsole %s%d\n",
2804 newcon
->name
, newcon
->index
);
2810 if (console_drivers
&& console_drivers
->flags
& CON_BOOT
)
2811 bcon
= console_drivers
;
2813 if (!has_preferred_console
|| bcon
|| !console_drivers
)
2814 has_preferred_console
= preferred_console
>= 0;
2817 * See if we want to use this console driver. If we
2818 * didn't select a console we take the first one
2819 * that registers here.
2821 if (!has_preferred_console
) {
2822 if (newcon
->index
< 0)
2824 if (newcon
->setup
== NULL
||
2825 newcon
->setup(newcon
, NULL
) == 0) {
2826 newcon
->flags
|= CON_ENABLED
;
2827 if (newcon
->device
) {
2828 newcon
->flags
|= CON_CONSDEV
;
2829 has_preferred_console
= true;
2834 /* See if this console matches one we selected on the command line */
2835 err
= try_enable_new_console(newcon
, true);
2837 /* If not, try to match against the platform default(s) */
2839 err
= try_enable_new_console(newcon
, false);
2841 /* printk() messages are not printed to the Braille console. */
2842 if (err
|| newcon
->flags
& CON_BRL
)
2846 * If we have a bootconsole, and are switching to a real console,
2847 * don't print everything out again, since when the boot console, and
2848 * the real console are the same physical device, it's annoying to
2849 * see the beginning boot messages twice
2851 if (bcon
&& ((newcon
->flags
& (CON_CONSDEV
| CON_BOOT
)) == CON_CONSDEV
))
2852 newcon
->flags
&= ~CON_PRINTBUFFER
;
2855 * Put this console in the list - keep the
2856 * preferred driver at the head of the list.
2859 if ((newcon
->flags
& CON_CONSDEV
) || console_drivers
== NULL
) {
2860 newcon
->next
= console_drivers
;
2861 console_drivers
= newcon
;
2863 newcon
->next
->flags
&= ~CON_CONSDEV
;
2864 /* Ensure this flag is always set for the head of the list */
2865 newcon
->flags
|= CON_CONSDEV
;
2867 newcon
->next
= console_drivers
->next
;
2868 console_drivers
->next
= newcon
;
2871 if (newcon
->flags
& CON_EXTENDED
)
2872 nr_ext_console_drivers
++;
2874 if (newcon
->flags
& CON_PRINTBUFFER
) {
2876 * console_unlock(); will print out the buffered messages
2879 logbuf_lock_irqsave(flags
);
2881 * We're about to replay the log buffer. Only do this to the
2882 * just-registered console to avoid excessive message spam to
2883 * the already-registered consoles.
2885 * Set exclusive_console with disabled interrupts to reduce
2886 * race window with eventual console_flush_on_panic() that
2887 * ignores console_lock.
2889 exclusive_console
= newcon
;
2890 exclusive_console_stop_seq
= console_seq
;
2891 console_seq
= syslog_seq
;
2892 logbuf_unlock_irqrestore(flags
);
2895 console_sysfs_notify();
2898 * By unregistering the bootconsoles after we enable the real console
2899 * we get the "console xxx enabled" message on all the consoles -
2900 * boot consoles, real consoles, etc - this is to ensure that end
2901 * users know there might be something in the kernel's log buffer that
2902 * went to the bootconsole (that they do not see on the real console)
2904 pr_info("%sconsole [%s%d] enabled\n",
2905 (newcon
->flags
& CON_BOOT
) ? "boot" : "" ,
2906 newcon
->name
, newcon
->index
);
2908 ((newcon
->flags
& (CON_CONSDEV
| CON_BOOT
)) == CON_CONSDEV
) &&
2910 /* We need to iterate through all boot consoles, to make
2911 * sure we print everything out, before we unregister them.
2913 for_each_console(bcon
)
2914 if (bcon
->flags
& CON_BOOT
)
2915 unregister_console(bcon
);
2918 EXPORT_SYMBOL(register_console
);
2920 int unregister_console(struct console
*console
)
2922 struct console
*con
;
2925 pr_info("%sconsole [%s%d] disabled\n",
2926 (console
->flags
& CON_BOOT
) ? "boot" : "" ,
2927 console
->name
, console
->index
);
2929 res
= _braille_unregister_console(console
);
2937 if (console_drivers
== console
) {
2938 console_drivers
=console
->next
;
2941 for_each_console(con
) {
2942 if (con
->next
== console
) {
2943 con
->next
= console
->next
;
2951 goto out_disable_unlock
;
2953 if (console
->flags
& CON_EXTENDED
)
2954 nr_ext_console_drivers
--;
2957 * If this isn't the last console and it has CON_CONSDEV set, we
2958 * need to set it on the next preferred console.
2960 if (console_drivers
!= NULL
&& console
->flags
& CON_CONSDEV
)
2961 console_drivers
->flags
|= CON_CONSDEV
;
2963 console
->flags
&= ~CON_ENABLED
;
2965 console_sysfs_notify();
2968 res
= console
->exit(console
);
2973 console
->flags
&= ~CON_ENABLED
;
2978 EXPORT_SYMBOL(unregister_console
);
2981 * Initialize the console device. This is called *early*, so
2982 * we can't necessarily depend on lots of kernel help here.
2983 * Just do some early initializations, and do the complex setup
2986 void __init
console_init(void)
2990 initcall_entry_t
*ce
;
2992 /* Setup the default TTY line discipline. */
2996 * set up the console device so that later boot sequences can
2997 * inform about problems etc..
2999 ce
= __con_initcall_start
;
3000 trace_initcall_level("console");
3001 while (ce
< __con_initcall_end
) {
3002 call
= initcall_from_entry(ce
);
3003 trace_initcall_start(call
);
3005 trace_initcall_finish(call
, ret
);
3011 * Some boot consoles access data that is in the init section and which will
3012 * be discarded after the initcalls have been run. To make sure that no code
3013 * will access this data, unregister the boot consoles in a late initcall.
3015 * If for some reason, such as deferred probe or the driver being a loadable
3016 * module, the real console hasn't registered yet at this point, there will
3017 * be a brief interval in which no messages are logged to the console, which
3018 * makes it difficult to diagnose problems that occur during this time.
3020 * To mitigate this problem somewhat, only unregister consoles whose memory
3021 * intersects with the init section. Note that all other boot consoles will
3022 * get unregistred when the real preferred console is registered.
3024 static int __init
printk_late_init(void)
3026 struct console
*con
;
3029 for_each_console(con
) {
3030 if (!(con
->flags
& CON_BOOT
))
3033 /* Check addresses that might be used for enabled consoles. */
3034 if (init_section_intersects(con
, sizeof(*con
)) ||
3035 init_section_contains(con
->write
, 0) ||
3036 init_section_contains(con
->read
, 0) ||
3037 init_section_contains(con
->device
, 0) ||
3038 init_section_contains(con
->unblank
, 0) ||
3039 init_section_contains(con
->data
, 0)) {
3041 * Please, consider moving the reported consoles out
3042 * of the init section.
3044 pr_warn("bootconsole [%s%d] uses init memory and must be disabled even before the real one is ready\n",
3045 con
->name
, con
->index
);
3046 unregister_console(con
);
3049 ret
= cpuhp_setup_state_nocalls(CPUHP_PRINTK_DEAD
, "printk:dead", NULL
,
3050 console_cpu_notify
);
3052 ret
= cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN
, "printk:online",
3053 console_cpu_notify
, NULL
);
3057 late_initcall(printk_late_init
);
3059 #if defined CONFIG_PRINTK
3061 * Delayed printk version, for scheduler-internal messages:
3063 #define PRINTK_PENDING_WAKEUP 0x01
3064 #define PRINTK_PENDING_OUTPUT 0x02
3066 static DEFINE_PER_CPU(int, printk_pending
);
3068 static void wake_up_klogd_work_func(struct irq_work
*irq_work
)
3070 int pending
= __this_cpu_xchg(printk_pending
, 0);
3072 if (pending
& PRINTK_PENDING_OUTPUT
) {
3073 /* If trylock fails, someone else is doing the printing */
3074 if (console_trylock())
3078 if (pending
& PRINTK_PENDING_WAKEUP
)
3079 wake_up_interruptible(&log_wait
);
3082 static DEFINE_PER_CPU(struct irq_work
, wake_up_klogd_work
) = {
3083 .func
= wake_up_klogd_work_func
,
3084 .flags
= ATOMIC_INIT(IRQ_WORK_LAZY
),
3087 void wake_up_klogd(void)
3089 if (!printk_percpu_data_ready())
3093 if (waitqueue_active(&log_wait
)) {
3094 this_cpu_or(printk_pending
, PRINTK_PENDING_WAKEUP
);
3095 irq_work_queue(this_cpu_ptr(&wake_up_klogd_work
));
3100 void defer_console_output(void)
3102 if (!printk_percpu_data_ready())
3106 __this_cpu_or(printk_pending
, PRINTK_PENDING_OUTPUT
);
3107 irq_work_queue(this_cpu_ptr(&wake_up_klogd_work
));
3111 int vprintk_deferred(const char *fmt
, va_list args
)
3115 r
= vprintk_emit(0, LOGLEVEL_SCHED
, NULL
, fmt
, args
);
3116 defer_console_output();
3121 int printk_deferred(const char *fmt
, ...)
3126 va_start(args
, fmt
);
3127 r
= vprintk_deferred(fmt
, args
);
3134 * printk rate limiting, lifted from the networking subsystem.
3136 * This enforces a rate limit: not more than 10 kernel messages
3137 * every 5s to make a denial-of-service attack impossible.
3139 DEFINE_RATELIMIT_STATE(printk_ratelimit_state
, 5 * HZ
, 10);
3141 int __printk_ratelimit(const char *func
)
3143 return ___ratelimit(&printk_ratelimit_state
, func
);
3145 EXPORT_SYMBOL(__printk_ratelimit
);
3148 * printk_timed_ratelimit - caller-controlled printk ratelimiting
3149 * @caller_jiffies: pointer to caller's state
3150 * @interval_msecs: minimum interval between prints
3152 * printk_timed_ratelimit() returns true if more than @interval_msecs
3153 * milliseconds have elapsed since the last time printk_timed_ratelimit()
3156 bool printk_timed_ratelimit(unsigned long *caller_jiffies
,
3157 unsigned int interval_msecs
)
3159 unsigned long elapsed
= jiffies
- *caller_jiffies
;
3161 if (*caller_jiffies
&& elapsed
<= msecs_to_jiffies(interval_msecs
))
3164 *caller_jiffies
= jiffies
;
3167 EXPORT_SYMBOL(printk_timed_ratelimit
);
3169 static DEFINE_SPINLOCK(dump_list_lock
);
3170 static LIST_HEAD(dump_list
);
3173 * kmsg_dump_register - register a kernel log dumper.
3174 * @dumper: pointer to the kmsg_dumper structure
3176 * Adds a kernel log dumper to the system. The dump callback in the
3177 * structure will be called when the kernel oopses or panics and must be
3178 * set. Returns zero on success and %-EINVAL or %-EBUSY otherwise.
3180 int kmsg_dump_register(struct kmsg_dumper
*dumper
)
3182 unsigned long flags
;
3185 /* The dump callback needs to be set */
3189 spin_lock_irqsave(&dump_list_lock
, flags
);
3190 /* Don't allow registering multiple times */
3191 if (!dumper
->registered
) {
3192 dumper
->registered
= 1;
3193 list_add_tail_rcu(&dumper
->list
, &dump_list
);
3196 spin_unlock_irqrestore(&dump_list_lock
, flags
);
3200 EXPORT_SYMBOL_GPL(kmsg_dump_register
);
3203 * kmsg_dump_unregister - unregister a kmsg dumper.
3204 * @dumper: pointer to the kmsg_dumper structure
3206 * Removes a dump device from the system. Returns zero on success and
3207 * %-EINVAL otherwise.
3209 int kmsg_dump_unregister(struct kmsg_dumper
*dumper
)
3211 unsigned long flags
;
3214 spin_lock_irqsave(&dump_list_lock
, flags
);
3215 if (dumper
->registered
) {
3216 dumper
->registered
= 0;
3217 list_del_rcu(&dumper
->list
);
3220 spin_unlock_irqrestore(&dump_list_lock
, flags
);
3225 EXPORT_SYMBOL_GPL(kmsg_dump_unregister
);
3227 static bool always_kmsg_dump
;
3228 module_param_named(always_kmsg_dump
, always_kmsg_dump
, bool, S_IRUGO
| S_IWUSR
);
3230 const char *kmsg_dump_reason_str(enum kmsg_dump_reason reason
)
3233 case KMSG_DUMP_PANIC
:
3235 case KMSG_DUMP_OOPS
:
3237 case KMSG_DUMP_EMERG
:
3239 case KMSG_DUMP_SHUTDOWN
:
3245 EXPORT_SYMBOL_GPL(kmsg_dump_reason_str
);
3248 * kmsg_dump - dump kernel log to kernel message dumpers.
3249 * @reason: the reason (oops, panic etc) for dumping
3251 * Call each of the registered dumper's dump() callback, which can
3252 * retrieve the kmsg records with kmsg_dump_get_line() or
3253 * kmsg_dump_get_buffer().
3255 void kmsg_dump(enum kmsg_dump_reason reason
)
3257 struct kmsg_dumper
*dumper
;
3258 unsigned long flags
;
3261 list_for_each_entry_rcu(dumper
, &dump_list
, list
) {
3262 enum kmsg_dump_reason max_reason
= dumper
->max_reason
;
3265 * If client has not provided a specific max_reason, default
3266 * to KMSG_DUMP_OOPS, unless always_kmsg_dump was set.
3268 if (max_reason
== KMSG_DUMP_UNDEF
) {
3269 max_reason
= always_kmsg_dump
? KMSG_DUMP_MAX
:
3272 if (reason
> max_reason
)
3275 /* initialize iterator with data about the stored records */
3276 dumper
->active
= true;
3278 logbuf_lock_irqsave(flags
);
3279 dumper
->cur_seq
= clear_seq
;
3280 dumper
->next_seq
= prb_next_seq(prb
);
3281 logbuf_unlock_irqrestore(flags
);
3283 /* invoke dumper which will iterate over records */
3284 dumper
->dump(dumper
, reason
);
3286 /* reset iterator */
3287 dumper
->active
= false;
3293 * kmsg_dump_get_line_nolock - retrieve one kmsg log line (unlocked version)
3294 * @dumper: registered kmsg dumper
3295 * @syslog: include the "<4>" prefixes
3296 * @line: buffer to copy the line to
3297 * @size: maximum size of the buffer
3298 * @len: length of line placed into buffer
3300 * Start at the beginning of the kmsg buffer, with the oldest kmsg
3301 * record, and copy one record into the provided buffer.
3303 * Consecutive calls will return the next available record moving
3304 * towards the end of the buffer with the youngest messages.
3306 * A return value of FALSE indicates that there are no more records to
3309 * The function is similar to kmsg_dump_get_line(), but grabs no locks.
3311 bool kmsg_dump_get_line_nolock(struct kmsg_dumper
*dumper
, bool syslog
,
3312 char *line
, size_t size
, size_t *len
)
3314 struct printk_info info
;
3315 unsigned int line_count
;
3316 struct printk_record r
;
3320 prb_rec_init_rd(&r
, &info
, line
, size
);
3322 if (!dumper
->active
)
3325 /* Read text or count text lines? */
3327 if (!prb_read_valid(prb
, dumper
->cur_seq
, &r
))
3329 l
= record_print_text(&r
, syslog
, printk_time
);
3331 if (!prb_read_valid_info(prb
, dumper
->cur_seq
,
3332 &info
, &line_count
)) {
3335 l
= get_record_print_text_size(&info
, line_count
, syslog
,
3340 dumper
->cur_seq
= r
.info
->seq
+ 1;
3349 * kmsg_dump_get_line - retrieve one kmsg log line
3350 * @dumper: registered kmsg dumper
3351 * @syslog: include the "<4>" prefixes
3352 * @line: buffer to copy the line to
3353 * @size: maximum size of the buffer
3354 * @len: length of line placed into buffer
3356 * Start at the beginning of the kmsg buffer, with the oldest kmsg
3357 * record, and copy one record into the provided buffer.
3359 * Consecutive calls will return the next available record moving
3360 * towards the end of the buffer with the youngest messages.
3362 * A return value of FALSE indicates that there are no more records to
3365 bool kmsg_dump_get_line(struct kmsg_dumper
*dumper
, bool syslog
,
3366 char *line
, size_t size
, size_t *len
)
3368 unsigned long flags
;
3371 logbuf_lock_irqsave(flags
);
3372 ret
= kmsg_dump_get_line_nolock(dumper
, syslog
, line
, size
, len
);
3373 logbuf_unlock_irqrestore(flags
);
3377 EXPORT_SYMBOL_GPL(kmsg_dump_get_line
);
3380 * kmsg_dump_get_buffer - copy kmsg log lines
3381 * @dumper: registered kmsg dumper
3382 * @syslog: include the "<4>" prefixes
3383 * @buf: buffer to copy the line to
3384 * @size: maximum size of the buffer
3385 * @len: length of line placed into buffer
3387 * Start at the end of the kmsg buffer and fill the provided buffer
3388 * with as many of the *youngest* kmsg records that fit into it.
3389 * If the buffer is large enough, all available kmsg records will be
3390 * copied with a single call.
3392 * Consecutive calls will fill the buffer with the next block of
3393 * available older records, not including the earlier retrieved ones.
3395 * A return value of FALSE indicates that there are no more records to
3398 bool kmsg_dump_get_buffer(struct kmsg_dumper
*dumper
, bool syslog
,
3399 char *buf
, size_t size
, size_t *len
)
3401 struct printk_info info
;
3402 unsigned int line_count
;
3403 struct printk_record r
;
3404 unsigned long flags
;
3409 bool time
= printk_time
;
3411 prb_rec_init_rd(&r
, &info
, buf
, size
);
3413 if (!dumper
->active
|| !buf
|| !size
)
3416 logbuf_lock_irqsave(flags
);
3417 if (dumper
->cur_seq
< prb_first_valid_seq(prb
)) {
3418 /* messages are gone, move to first available one */
3419 dumper
->cur_seq
= prb_first_valid_seq(prb
);
3423 if (dumper
->cur_seq
>= dumper
->next_seq
) {
3424 logbuf_unlock_irqrestore(flags
);
3428 /* calculate length of entire buffer */
3429 seq
= dumper
->cur_seq
;
3430 while (prb_read_valid_info(prb
, seq
, &info
, &line_count
)) {
3431 if (r
.info
->seq
>= dumper
->next_seq
)
3433 l
+= get_record_print_text_size(&info
, line_count
, true, time
);
3434 seq
= r
.info
->seq
+ 1;
3437 /* move first record forward until length fits into the buffer */
3438 seq
= dumper
->cur_seq
;
3439 while (l
>= size
&& prb_read_valid_info(prb
, seq
,
3440 &info
, &line_count
)) {
3441 if (r
.info
->seq
>= dumper
->next_seq
)
3443 l
-= get_record_print_text_size(&info
, line_count
, true, time
);
3444 seq
= r
.info
->seq
+ 1;
3447 /* last message in next interation */
3450 /* actually read text into the buffer now */
3452 while (prb_read_valid(prb
, seq
, &r
)) {
3453 if (r
.info
->seq
>= dumper
->next_seq
)
3456 l
+= record_print_text(&r
, syslog
, time
);
3458 /* adjust record to store to remaining buffer space */
3459 prb_rec_init_rd(&r
, &info
, buf
+ l
, size
- l
);
3461 seq
= r
.info
->seq
+ 1;
3464 dumper
->next_seq
= next_seq
;
3466 logbuf_unlock_irqrestore(flags
);
3472 EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer
);
3475 * kmsg_dump_rewind_nolock - reset the iterator (unlocked version)
3476 * @dumper: registered kmsg dumper
3478 * Reset the dumper's iterator so that kmsg_dump_get_line() and
3479 * kmsg_dump_get_buffer() can be called again and used multiple
3480 * times within the same dumper.dump() callback.
3482 * The function is similar to kmsg_dump_rewind(), but grabs no locks.
3484 void kmsg_dump_rewind_nolock(struct kmsg_dumper
*dumper
)
3486 dumper
->cur_seq
= clear_seq
;
3487 dumper
->next_seq
= prb_next_seq(prb
);
3491 * kmsg_dump_rewind - reset the iterator
3492 * @dumper: registered kmsg dumper
3494 * Reset the dumper's iterator so that kmsg_dump_get_line() and
3495 * kmsg_dump_get_buffer() can be called again and used multiple
3496 * times within the same dumper.dump() callback.
3498 void kmsg_dump_rewind(struct kmsg_dumper
*dumper
)
3500 unsigned long flags
;
3502 logbuf_lock_irqsave(flags
);
3503 kmsg_dump_rewind_nolock(dumper
);
3504 logbuf_unlock_irqrestore(flags
);
3506 EXPORT_SYMBOL_GPL(kmsg_dump_rewind
);