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

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Date:	Fri, 01 Nov 2013 21:08:26 +0100
From:	Richard Weinberger <richard@....at>
To:	Seiji Aguchi <seiji.aguchi@....com>
CC:	Tony Luck <tony.luck@...il.com>, 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

Am 01.11.2013 20:22, schrieb Seiji Aguchi:
>>>> +{
>>>> +       char id_str[64];
>>>> +       u64 id = 0;
>>>> +
>>>> +       sprintf(id_str, "%lu%u%d", timestamp, part, count);
>>>> +       if (kstrtoull(id_str, 10, &id))
>>>> +               pr_warn("efi-pstore: failed to generate id\n");
>>>> +       return id;
>>>> +}
>>>
>>> This is just odd. You make a string from three ints and then a parse
>>> it to a int again.
>>
>> Agreed.  I liked your ((timestamp * 100 + part) * 100 + count function much
>> more than this.
> 
> I was worried that the part and count could be more than 100.
> If it happens, the id may not be unique...
> 
> But, currently, size of nvram storage is limited, so it is a corner case.
> I respect your opinion.

What about feeding the bytes of all three integers into a non-cryptographic hash function?
Using this way you get a cheap unique id.

Thanks,
//richard
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