[linux-yocto] [PATCH][v5.2/standard/preempt-rt/base] printk: devkmsg: read: Return EPIPE when the first message user-space wants has gone

[Bruce Ashfield]

I didn't merge this directly, but instead updated the -rt branches to
-rt9 .. so I got your change that way.

Cheers,

Bruce

On Sun, Sep 29, 2019 at 5:36 AM <zhe.he at windriver.com> wrote:
>
> From: He Zhe <zhe.he at windriver.com>
>
> This fixes ltp failure,
> kmsg01.c:444: FAIL: read returned: 56: SUCCESS
>
> When user-space wants to read the first message, that is when user->seq
> is 0, and that message has gone, it currently automatically resets
> user->seq to current first seq. This mis-aligns with mainline kernel.
>
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/ABI/testing/dev-kmsg#n39
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/kernel/printk/printk.c#n899
>
> We should inform user-space that what it wants has gone by returning EPIPE
> in such scenario.
>
> Link: https://lore.kernel.org/linux-rt-users/8736gls1aj.fsf@linutronix.de/T/#t
>
> Signed-off-by: He Zhe <zhe.he at windriver.com>
> ---
>  kernel/printk/printk.c | 12 ++++--------
>  1 file changed, 4 insertions(+), 8 deletions(-)
>
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index e3fa33f..58c545a 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -703,14 +703,10 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
>                 goto out;
>         }
>
> -       if (user->seq == 0) {
> -               user->seq = seq;
> -       } else {
> -               user->seq++;
> -               if (user->seq < seq) {
> -                       ret = -EPIPE;
> -                       goto restore_out;
> -               }
> +       user->seq++;
> +       if (user->seq < seq) {
> +               ret = -EPIPE;
> +               goto restore_out;
>         }
>
>         msg = (struct printk_log *)&user->msgbuf[0];
> --
> 2.7.4
>


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