Re: [PATCH] printk: add KERN_NOTIME to skip the timestamp

From: xiang xiao
Date: Wed Feb 13 2019 - 03:53:12 EST


On Wed, Feb 13, 2019 at 4:08 PM Sergey Senozhatsky
<sergey.senozhatsky.work@xxxxxxxxx> wrote:
>
> On (02/13/19 15:14), xiang xiao wrote:
> >
> > But how can I precisely control timestamp on/off per message
> > through sysfs node?
> >
>
> Hmm. I don't know how many kernel printk-s you have and how often
> do you write to kmsg.

It depend on use case, but I plan to create a generic driver which
could reuse by all rpmsg based remoteproc.
This is the driver for upstream:
https://github.com/thesofproject/linux/pull/177/commits/a0b7009fede5552dc98733f2996a8140bff62455
so we need more precisely control here.

> I was thinking about something like this:
>

> echo 0 > /...printk.../time
> dump buffer to /dev/kmsg
> echo 1 > /...printk../time
>

Another problem is how to control sysfs node from driver code
naturally, the concurrency and global side effect also need to
address.

> - If you would have several kernel printk-s in the meantime, then
> those would not have timestamps, but you kinda can roughly guess
> it
>
> write [1243] foo > /dev/kmsg
> write [1244] foo > /dev/kmsg
> << printk(bar) <timestamp ~[1244,1245]>
> write [1245] foo > /dev/kmsg
>
> Maybe this won't suffice.
>
> -ss