linux-kernel - Re: [PATCH] Make efi-pstore return a unique id

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Date:	Fri, 1 Nov 2013 17:17:00 -0700
From:	Tony Luck <tony.luck@...il.com>
To:	Seiji Aguchi <seiji.aguchi@....com>
Cc:	Richard Weinberger <richard@....at>, Madper Xie <cxie@...hat.com>,
	"matt.fleming@...el.com" <matt.fleming@...el.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Linux EFI <linux-efi@...r.kernel.org>,
	谢成骏 <bbboson@...il.com>
Subject: Re: [PATCH] Make efi-pstore return a unique id

On Fri, Nov 1, 2013 at 1:57 PM, Seiji Aguchi <seiji.aguchi@....com> wrote:
>> What about feeding the bytes of all three integers into a non-cryptographic hash function?
>> Using this way you get a cheap unique id.
>
> It is reasonable to me.

How does efivars backend handle "unlink(2)" in the pstore file system.
pstore will call the backend->erase function passing the "id".  The
backend should then erase the right record from persistent storage.

With the  ((timestamp * 100 + part) * 100 + count function - you can
easily reverse it to find timestamp, part and count - would that make life
easier for the backend to find the record to be erased?  If you use a
hash function you will need to check each record and compute the
hash to see if it matches (probably not a big deal because the backend
will generally only hold a handful of records).

-Tony
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