linux-kernel - Re: [PATCH] zram: fix bug storing backing

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Date:   Tue, 21 Aug 2018 18:28:51 -0700
From:   Peter Kalauskas <peskal@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     Minchan Kim <minchan@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] zram: fix bug storing backing_dev

On Tue, Aug 14, 2018 at 04:45:23PM -0700, Andrew Morton wrote:
> The changelog doesn't describe the end-user impact of the bug, which is
> very desirable when tagging a patch for -stable backporting.  Can we
> have that paragraph please?

The end-user impact is that echoing to writeback_dev would not cause it
to change. Would the following statement suffice?

  Without this change, it is not possible to change writeback_dev unless
  the tool used to do so does not include a newline character.  For
  example, 'echo -n' or 'printf' would work, but 'echo' would not work.

I can also include Sergey's description of the bug if that would be
helpful.

On Thu, Aug 16, 2018 at 10:48:35AM +0900, Sergey Senozhatsky wrote:
> On (08/14/18 16:45), Andrew Morton wrote:
> > >
> > > > > -     strlcpy(file_name, buf, len);
> > >
> > > This is quite interesting. The reason it worked before was the fact that
> > > strlcpy() copies 'len - 1' bytes, which is strlen(buf) - 1 in our case,
> > > so it accidentally didn't copy the trailing new line symbol. Which also
> > > means that "echo -n /dev/sdX" most likely was broken.
> > >
> >
> > I can't find the original email on lkml for some reason, but I
> > recreated the patch.
>
> Neither can I.
>

Sorry, I sent it to Minchan directly. I'll send PATCH v2 to lkml, if v2
is needed.

On Wed, Aug 15, 2018 at 08:32:26PM -0700, Andrew Morton wrote:
> On Thu, 16 Aug 2018 10:48:35 +0900 Sergey Senozhatsky <sergey.senozhatsky.work@...il.com> wrote:
>
> > > The implementation might be able to use strim() somehow.
> >
> > strim() trims white-spaces.
>
> Which includes \n.
>

The if statement is already used by comp_algorithm_store in zram_drv.c,
so perhaps it should remain the if statement for consistency. What do
you think, should I use strim or the if statement?