dmesg: add caller_id support

dmesg: add caller_id support

Submission to Project: util-linux
Open Incident: #2609 at github.com/util-linux/util-linux/issues/2609
Component: util-linux/sys-utils
File: dmesg.c
Code level patch applied against: 2.39.3 - latest code pulled from
           git.github.com:util-linux/util-linux.git
Revision: #1 on 2023/12/08 per Review from Karel Zak
Revision: #2 on 2023/12/12 Adjust line offsets for master update and
                           Add caller_id_size init to dmesg -K
Revision: #3 on 2023/12/12 Use of sizeof for cidbuf and limit search
                           for caller_id to dmesg prefix to msg text
Revision: #4 on 2023/12/15 Ensure SYSLOG and kmsg inputs have
                           caller_id_size set appropriately
Revision: #5 on 2023/12/24 Make caller_id width consistent with
                           makedumpfile
Revision: #6 on 2023/12/30 Use updated test naming convention
Revision: #7 on 2024/01/04 Normalize kmsg caller_id spacing for test
                           platforms by removing caller_id padding
                           in test generated output.

Add support to standard dmesg command for the optional Linux Kernel
debug CONFIG option PRINTK_CALLER which adds an optional dmesg field
that contains the Thread Id or CPU Id that is issuing the printk to
add the message to the kernel ring buffer. This makes debugging simpler
as dmesg entries for a specific thread or CPU can be recognized.

The dmesg -S using the old syslog interface supports printing the
PRINTK_CALLER field but currently standard dmesg does not support
printing the field if present. There are utilities that use dmesg and
so it would be optimal if dmesg supported PRINTK_CALLER as well.

The additional field provided by PRINTK_CALLER is only present
if it was configured for the Linux kernel where the dmesg command
is run. It is a debug option and not configured by default so the
dmesg output will only change for those kernels where the option was
configured when the kernel was built. For users who went to the
trouble to configure PRINTK_CALLER and have the extra field available
for debugging, having dmesg print the field is very helpful.

Size of the PRINTK_CALLER field is determined by the maximum number
tasks that can be run on the system which is limited by the value of
/proc/sys/kernel/pid_max as pid values are from 0 to value - 1.
This value determines the number of id digits needed by the caller id.
The PRINTK_CALLER field is printed as T<id> for a Task Id or C<id>
for a CPU Id for a printk in CPU context. The values are left space
padded and enclosed in parentheses such as: [    T123] or [     C16]

For consistency with dmesg -S which supports the PRINTK_CALLER field
the field is printed followed by a space. For JSON format output the
PRINTK_CALLER field is identified as caller as that is consistent with
it's naming in /dev/kmsg. No space padding is used to reduce space
consumed by the JSON output. So the output from the command on a system
with PRINTK_CALLER field enabled in the Linux .config file the dmesg
output appears as:

> dmesg
...
[  520.897104] [   T3919] usb 3-3: Product: USB 2.0 Hub

and

> dmesg -x
...
kern  :info  : [  520.897104] [   T3919] usb 3-3: Product: USB 2.0 Hub

and

> dmesg -J
...
      },{
         "pri": 6,
         "time":    520.897104,
         "caller": "T3919",
         "msg": "usb 3-3: Product: USB 2.0 Hub"
      },{

and

> dmesg -J -x
...
      },{
         "fac": "kern",
         "pri": "info",
         "time":   520.897104,
         "caller": "T3919",
         "msg": "usb 3-3: Product: USB 2.0 Hub"
      },{

>

For comparison:

> dmesg -S
...
[  520.897104] [ T3919] usb 3-3: Product: USB 2.0 Hub

and

> dmesg -S -x
...
kern  :info  : [  520.897104] [ T3919] usb 3-3: Product: USB 2.0 Hub

Note: When dmesg uses the old syslog interface the reserved space for
      the PRINTK_CALLER field is capped at 5 digits because 32-bit
      kernels are capped at 32768 as the max number of PIDs. However,
      64-bit systems are currently capped at 2^22 PIDs (0 - 4194303).
      The PID cap is set by PID_MAX_LIMIT but the system limit can be
      less so we use /proc/sys/kernel/pid_max to determine the size
      needed to hold the maximum PID value size for the current system.
      Many 64-bit systems support 2^22 PIDs (0 - 4194303) and you see:

> dmesg -x
...
kern  :info  : [  520.899558] [   T3919] hub 3-3:1.0: USB hub found
...
kern  :info  : [ 9830.456898] [  T98982] cgroup: fork rejected by pids ...
kern  :info  : [14301.158878] [ T137336] cgroup: fork rejected by pids ...
kern  :info  : [18980.803190] [T1637865] cgroup: fork rejected by pids ...

> dmesg -S -x
...
kern  :info  : [  520.899558] [ T3919] hub 3-3:1.0: USB hub found
...
kern  :info  : [ 9830.456898] [T98982] cgroup: fork rejected by pids ...
kern  :info  : [14301.158878] [T137336] cgroup: fork rejected by pids ...
kern  :info  : [18980.803190] [T1637865] cgroup: fork rejected by pids ...

This is the only difference seen with PRINTK_CALLER configured and
printing between the dmesg /dev/kmsg interface and the dmesg -S syslog
interface.

Tests naming has been revised based on naming convention Thomas used to
introduce dmest json tests. The naming of test and input files that
reside in tests/ts/dmeg include:

<name> are existing dmesg syslog interface tests and input files.
cid-<name> are dmesg syslog interface caller_id tests and input files.
json-<name> are dmesg kmsg interface tests and input files.
cid-json-<name> are dmesg kmsg interface caller_id tests and input files.

Resulting expected files match the test names.

Signed-off-by: Ivan Delalande <colona@arista.com>
Signed-off-by: Edward Chron <echron@arista.com>
Signed-off-by: Karel Zak <kzak@redhat.com>