linux-kernel - Re: [PATCH 19/20] pstore: fs superblock limits

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Message-ID: <CABeXuvrmNkUOH5ZU59Kg4Ge1cFE9nqp9NhTPJjus5KkCrYeC6w@mail.gmail.com>
Date:   Thu, 1 Aug 2019 19:26:21 -0700
From:   Deepa Dinamani <deepa.kernel@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Kees Cook <keescook@...omium.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
        y2038 Mailman List <y2038@...ts.linaro.org>,
        Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH 19/20] pstore: fs superblock limits

On Tue, Jul 30, 2019 at 12:36 AM Arnd Bergmann <arnd@...db.de> wrote:
>
> On Tue, Jul 30, 2019 at 6:31 AM Kees Cook <keescook@...omium.org> wrote:
> >
> > On Mon, Jul 29, 2019 at 06:49:23PM -0700, Deepa Dinamani wrote:
> > > Also update the gran since pstore has microsecond granularity.
> >
> > So, I'm fine with this, but technically the granularity depends on the
> > backend storage... many have no actual time keeping, though. My point is,
> > pstore's timestamps are really mostly a lie, but the most common backend
> > (ramoops) is seconds-granularity.
> >
> > So, I'm fine with this, but it's a lie but it's a lie that doesn't
> > matter, so ...
> >
> > Acked-by: Kees Cook <keescook@...omium.org>
> >
> > I'm open to suggestions to improve it...
>
> If we don't care about using sub-second granularity, then setting it
> to one second unconditionally here will make it always use that and
> report it correctly.

Should this printf in ramoops_write_kmsg_hdr() also be fixed then?

        RAMOOPS_KERNMSG_HDR "%lld.%06lu-%c\n",
        (time64_t)record->time.tv_sec,
        record->time.tv_nsec / 1000,
        record->compressed ? 'C' : 'D');
    persistent_ram_write(prz, hdr, len);

ramoops_read_kmsg_hdr() doesn't read this as microseconds. Seems like
a mismatch from above.

If we want to agree that we just want seconds granularity for pstore,
we could replace the tv_nsec part to be all 0's if anybody else is
depending on this format.
I could drop this patch from the series and post that patch seperately.

Thanks,
-Deepa