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 14:19:59 -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 1:51 PM, Seiji Aguchi <seiji.aguchi@....com> wrote:
>> 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.
>
> Patch 2/5, 3/5 and 4/5 don't change an existing format of a variable name and don't break anything.
> The existing format consists of type, id and ctime. And it is not moditied by these patches.
> Here is a variable name (and guid) of efi_pstore in curret linus-tree.
>
>         ls /sys/firmware/efi/vars/
>         dump-type0-1-1351113059-cfc8fc79-be2e-4ddc-97f0-9f98bfe298a0
>         dump-type0-2-1351113059-cfc8fc79-be2e-4ddc-97f0-9f98bfe298a0
>         dump-type0-3-1351113059-cfc8fc79-be2e-4ddc-97f0-9f98bfe298a0
>
>         Variable Name: dump-type0-1-1351113059
>         GUID: cfc8fc79-be2e-4ddc-97f0-9f98bfe298a0

Okay, this alleviates most of my concerns for ctime.

>
> On the other hand, patch 5/5 changes the format by adding sequence counter.
> But efi_pstore_read is modied to work correctly in it.
>
>         dump-type0-1-1-1351113059-cfc8fc79-be2e-4ddc-97f0-9f98bfe298a0
>
>         Variable Name: dump-type0-1-1-1351113059
>         GUID: cfc8fc79-be2e-4ddc-97f0-9f98bfe298a0
>
> If I need to elaborate more, please feel free to ask me:)
> I'm not sure if I understand your question completely.

In this case, I think efi_pstore_read in patch 5/5 should probably
fall-back to trying to do a sscanf(...) == 3 if the sscanf(...) == 4
test fails so that dumps for older dumps from previous kernels are
still visible to users, no?  They can perhaps get a default count of
0?  efi_pstore_erase would have to be updated to understand this as
well.
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