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Date:   Mon, 11 May 2020 22:15:10 -0700
From:   Kees Cook <keescook@chromium.org>
To:     WeiXiong Liao <liaoweixiong@allwinnertech.com>
Cc:     Anton Vorontsov <anton@enomsg.org>,
        Colin Cross <ccross@android.com>,
        Tony Luck <tony.luck@intel.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Miquel Raynal <miquel.raynal@bootlin.com>,
        Richard Weinberger <richard@nod.at>,
        Vignesh Raghavendra <vigneshr@ti.com>,
        Rob Herring <robh@kernel.org>, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-mtd@lists.infradead.org
Subject: Re: [PATCH v8 01/11] pstore/zone: Introduce common layer to manage
 storage zones
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 <20200511233229.27745-2-keescook@chromium.org>
 <a9d47bf1-7498-1d07-a943-29dd0b0ef2e1@allwinnertech.com>
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On Tue, May 12, 2020 at 11:55:20AM +0800, WeiXiong Liao wrote:
> On 2020/5/12 AM 7:32, Kees Cook wrote:
> > [...]
> > +struct psz_context {
> > +	struct pstore_zone **kpszs;
> > +	unsigned int kmsg_max_cnt;
> > +	unsigned int kmsg_read_cnt;
> > +	unsigned int kmsg_write_cnt;
> > +	/*
> > +	 * These counters should be calculated during recovery.
> > +	 * It records the oops/panic times after crashes rather than boots.
> > +	 */
> > +	unsigned int oops_counter;
> > +	unsigned int panic_counter;
> 
> oops/panic_counter is designed to count the crash times since the
> linux kernel was installed. pstore/zone lookup the max counter from all
> valid kmsg zones when recovery and saves them to oops/panic_counter.
> However, they are unable to get real number if we remove files. It's
> not serious, we can fix it after this series.

Since the kernel was installed? I don't see a kernel version check in
here? Or do you mean "since ever", in that it's a rolling count?

> And since pstore supports "max_reason", should pstore/zone count for
> other reason?

For now, no. I opted to try to keep this as simple as possible a port
from dump_oops to max_reason for now.

> > +static inline int psz_kmsg_erase(struct psz_context *cxt,
> > +		struct pstore_zone *zone, struct pstore_record *record)
> > +{
> > +	struct psz_buffer *buffer = zone->buffer;
> > +	struct psz_kmsg_header *hdr =
> > +		(struct psz_kmsg_header *)buffer->data;
> > +
> > +	if (unlikely(!psz_ok(zone)))
> > +		return 0;
> > +	/* this zone is already updated, no need to erase */
> > +	if (record->count != hdr->counter)
> > +		return 0;
> 
> These codes is to fix bug that user remove files on pstore filesystem
> but kmsg zone is already updated and pstore/zone should not erase
> zone. It work for oops and panic because the count number is increasing.
> However, it's useless for other reason of kmsg. We can fix it after this
> series.

Okay, sounds good.

-- 
Kees Cook