Re: [PATCH] dmesg: Add force-prefix option

[Karel Zak <kzak@redhat.com>]

On Tue, Oct 31, 2017 at 08:01:31AM -0400, Prarit Bhargava wrote:
> The kernel outputs multi-line messages (kernel messages that contain
> the end-of-line character '\n').  These message are currently displayed by
> dmesg as
> 
> [965199.028940] runnable tasks:
>                            task   PID         tree-key  switches  prio
> wait-time             sum-exec        sum-sleep
>                 ----------------------------------------------------------------------------------------------------------
> 
> The kernel timestamps each of these lines with [965199.028940] and the
> dmesg utility should do the same.
> 
> Add the 'force-prefix'/'-p' dmesg option to add decode & timestamp information
> to each line of a multi-line message.
> 
> Notes: The new print_record() algorithm stores the decode & timestamp
> information in buffers.  If the force-prefix option is used, the message is
> split into separate lines and each line is prefixed with the stored decode &
> timestamp information.  The splitting of the message into separate lines is
> done using strtok() which requires write access to the message buffer (ie, the
> const message buffer is now copied into a writeable buffer).
> 
> Successfully tested by me by looking at sysrq-t and sysrq-w output.
> All known good /tests passed with these changes.

Merged with some changes:

     - use snprintf()
     - cleanup \n usage (don't count line break to the
       message text in the parsers  and always print \n after the text
     - add the option to the man page
     - use --force-prefix for kmsg only, old syslog(2) API splits messages itself
     - strdup() the message text only on force-prefix

Please, test it again :-)

    Karel

-- 
 Karel Zak  <kzak@redhat.com>
 http://karelzak.blogspot.com