Merge branch 'for-5.11-null-console' into for-linus

diff --git a/drivers/tty/Kconfig b/drivers/tty/Kconfig
index 93fd984eb2f5a43b4972b3a13bff726d215fd029..ca359bbd62f5f393cc118004933e5035d05ae1a3 100644 (file)
--- a/drivers/tty/Kconfig
+++ b/drivers/tty/Kconfig
@@ -428,20 +428,6 @@ config MIPS_EJTAG_FDC_KGDB_CHAN
        help
          FDC channel number to use for KGDB.
 
-config NULL_TTY
-       tristate "NULL TTY driver"
-       help
-         Say Y here if you want a NULL TTY which simply discards messages.
-
-         This is useful to allow userspace applications which expect a console
-         device to work without modifications even when no console is
-         available or desired.
-
-         In order to use this driver, you should redirect the console to this
-         TTY, or boot the kernel with console=ttynull.
-
-         If unsure, say N.
-
 config TRACE_ROUTER
        tristate "Trace data router for MIPI P1149.7 cJTAG standard"
        depends on TRACE_SINK

diff --git a/drivers/tty/Makefile b/drivers/tty/Makefile
index 020b1cd9294fdc3342cb145dda766cf4e00127a7..f6b6bee0422d753d84cd8826c4aa2b9c56bc169c 100644 (file)
--- a/drivers/tty/Makefile
+++ b/drivers/tty/Makefile
@@ -2,7 +2,7 @@
 obj-$(CONFIG_TTY)              += tty_io.o n_tty.o tty_ioctl.o tty_ldisc.o \
                                   tty_buffer.o tty_port.o tty_mutex.o \
                                   tty_ldsem.o tty_baudrate.o tty_jobctrl.o \
-                                  n_null.o
+                                  n_null.o ttynull.o
 obj-$(CONFIG_LEGACY_PTYS)      += pty.o
 obj-$(CONFIG_UNIX98_PTYS)      += pty.o
 obj-$(CONFIG_AUDIT)            += tty_audit.o
@@ -25,7 +25,6 @@ obj-$(CONFIG_ISI)             += isicom.o
 obj-$(CONFIG_MOXA_INTELLIO)    += moxa.o
 obj-$(CONFIG_MOXA_SMARTIO)     += mxser.o
 obj-$(CONFIG_NOZOMI)           += nozomi.o
-obj-$(CONFIG_NULL_TTY)         += ttynull.o
 obj-$(CONFIG_ROCKETPORT)       += rocket.o
 obj-$(CONFIG_SYNCLINK_GT)      += synclink_gt.o
 obj-$(CONFIG_SYNCLINKMP)       += synclinkmp.o

diff --git a/drivers/tty/ttynull.c b/drivers/tty/ttynull.c
index 17f05b7eb6d3ede3790d98d9527c7221eb907405..eced70ec54e174e0ae6d48ba90777ebcf08f5e4e 100644 (file)
--- a/drivers/tty/ttynull.c
+++ b/drivers/tty/ttynull.c
@@ -2,6 +2,13 @@
 /*
  * Copyright (C) 2019 Axis Communications AB
  *
+ * The console is useful for userspace applications which expect a console
+ * device to work without modifications even when no console is available
+ * or desired.
+ *
+ * In order to use this driver, you should redirect the console to this
+ * TTY, or boot the kernel with console=ttynull.
+ *
  * Based on ttyprintk.c:
  *  Copyright (C) 2010 Samo Pogacnik
  */
@@ -59,6 +66,17 @@ static struct console ttynull_console = {
        .device = ttynull_device,
 };
 
+void __init register_ttynull_console(void)
+{
+       if (!ttynull_driver)
+               return;
+
+       if (add_preferred_console(ttynull_console.name, 0, NULL))
+               return;
+
+       register_console(&ttynull_console);
+}
+
 static int __init ttynull_init(void)
 {
        struct tty_driver *driver;

diff --git a/include/linux/console.h b/include/linux/console.h
index 4b1e26c4cb4286603b0a381022fef0468bb8728c..9c662e41cde519ece7b9c382411a9b3fd94ae272 100644 (file)
--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -187,9 +187,12 @@ extern int braille_register_console(struct console *, int index,
 extern int braille_unregister_console(struct console *);
 #ifdef CONFIG_TTY
 extern void console_sysfs_notify(void);
+extern void register_ttynull_console(void);
 #else
 static inline void console_sysfs_notify(void)
 { }
+static inline void register_ttynull_console(void)
+{ }
 #endif
 extern bool console_suspend_enabled;
 

diff --git a/init/main.c b/init/main.c
index 20baced721ad44c5cb08e016f955388bbd27ceb9..08cd3a52a7e8d7e38117e32640666af947f5f98f 100644 (file)
--- a/init/main.c
+++ b/init/main.c
@@ -1480,8 +1480,14 @@ void __init console_on_rootfs(void)
        struct file *file = filp_open("/dev/console", O_RDWR, 0);
 
        if (IS_ERR(file)) {
-               pr_err("Warning: unable to open an initial console.\n");
-               return;
+               pr_err("Warning: unable to open an initial console. Fallback to ttynull.\n");
+               register_ttynull_console();
+
+               file = filp_open("/dev/console", O_RDWR, 0);
+               if (IS_ERR(file)) {
+                       pr_err("Warning: Failed to add ttynull console. No stdin, stdout, and stderr for the init process!\n");
+                       return;
+               }
        }
        init_dup(file);
        init_dup(file);

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index c8847ee571f0e1f22b022ceb99835e5813ac2702..ccbdac579bd0871c59c408e8dede694935aceb76 100644 (file)
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2236,8 +2236,15 @@ static int __init console_setup(char *str)
        char *s, *options, *brl_options = NULL;
        int idx;
 
-       if (str[0] == 0)
+       /*
+        * console="" or console=null have been suggested as a way to
+        * disable console output. Use ttynull that has been created
+        * for exacly this purpose.
+        */
+       if (str[0] == 0 || strcmp(str, "null") == 0) {
+               __add_preferred_console("ttynull", 0, NULL, NULL, true);
                return 1;
+       }
 
        if (_braille_console_setup(&str, &brl_options))
                return 1;