linux-kernel - Re: [PATCH v2 3/5] efi_pstore: Remove a logic erasing entries from a write callback to hold multiple logs

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Date:	Thu, 25 Oct 2012 13:21:48 -0700
From:	Mike Waychison <mikew@...gle.com>
To:	Seiji Aguchi <seiji.aguchi@....com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"Luck, Tony (tony.luck@...el.com)" <tony.luck@...el.com>,
	"Matthew Garrett (mjg@...hat.com)" <mjg@...hat.com>,
	"dzickus@...hat.com" <dzickus@...hat.com>,
	"dle-develop@...ts.sourceforge.net" 
	<dle-develop@...ts.sourceforge.net>,
	Satoru Moriya <satoru.moriya@....com>
Subject: Re: [PATCH v2 3/5] efi_pstore: Remove a logic erasing entries from a
 write callback to hold multiple logs

On Thu, Oct 25, 2012 at 1:03 PM, Seiji Aguchi <seiji.aguchi@....com> wrote:
>> > -               list_del(&found->list);
>> > +       sprintf(name, "dump-type%u-%u-%lu", type, part,
>> > +               get_seconds());
>>
>> Actually, nothing seems to be ensuring that the value used here ends up being the same as the ctime :\  Consider what happens if the
>> get_seconds() call here happens at second N, and the i_ctime is collected at time N+1. The object wouldn't be able to be deleted after
>> patch 4/5 is applied.  How can we better ensure that the i_ctime is the same value as serialized into the efi var name here?
>
>  i_ctime of pstore file system is different from normal file systems.
> As I said in patch v1, i_ctime of pstore means the date that the record was "originally" stored.
>
> I_ctime is always set to N.
> Here is the scenario.
>
> 1.  writing time
>     - get_seconds() call here happens at second N
>     - "N" is stored to a variable name
>
> 2. System reboots...
> 3. System boots up...
>
> 4. reading time
>    - pstore calls a read callback, efi_pstore_read()
>    -  efi_pstore_read extracts ctime, "N", from the virable name

Ah, I accidentally glossed over this bit.  Thanks for correcting me :)

>    -  efi_pstore passes "N" to pstore file system
>     - pstore create a file, /dev/pstore/dmesg* and set "N" to i_ctime
>
> Pstore file system doesn't set i_ctime by itself but set ctime passed by platform drivers.
>

So doesn't this break erasing of existing dumps in pstore-efivars?
Unless efi_pstore_read still understands the older variable name
formats, users will be stranded with dumps consuming space in efivars
that aren't exported via pstore anymore.
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