Message-ID: <476716BD.7060807@linux.intel.com>
Date: Mon, 17 Dec 2007 16:39:25 -0800
From: Arjan van de Ven <arjan@linux.intel.com>
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To: Linus Torvalds <torvalds@linux-foundation.org>
CC: Tony Luck <tony.luck@intel.com>, Ingo Molnar <mingo@elte.hu>,
       linux-kernel@vger.kernel.org, Andrew Morton <akpm@linux-foundation.org>,
       protasnb@gmail.com, tytso@thunk.org
Subject: Re: Top kernel oopses/warnings this week
References: <4762CF8C.90808@linux.intel.com> <20071217172331.GA23070@elte.hu> <20071217133631.5bbc5842@laptopd505.fenrus.org> <12c511ca0712171458n1bc05b40nab6b4b7c92433c8d@mail.gmail.com> <476703A4.7000401@linux.intel.com> <12c511ca0712171526h242a7de8vadec78cd48747bd@mail.gmail.com> <20071217154727.404e4bc4@laptopd505.fenrus.org> <alpine.LFD.0.9999.0712171607370.21557@woody.linux-foundation.org>
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Linus Torvalds wrote:
> 
> On Mon, 17 Dec 2007, Arjan van de Ven wrote:
>> +char *get_boot_uuid(void)
>> +{
>> +	static char target[38];
>> +	unsigned char *uuid;
>> +
>> +	if (sysctl_bootid[8] == 0)
>> +		generate_random_uuid(sysctl_bootid);
>> +	/* sysctl_bootid is signed, to print we need unsigned .. */
>> +	uuid = sysctl_bootid;
>> +
>> +	if (target[0] == 0) {
>> +		sprintf(target, "%02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x-"
>> +			"%02x%02x%02x%02x%02x%02x",
> 
> Why isn't *everything* inside that "if (target[0] == 0" check?

the sysctl_bootid is shared with the /proc exposed bootid, so I need to generate it the same way

> I'd _also_ suggest that you'd actually try to avoid that horrid sequence 
> of "%02x..", and instead just make sure that sysctl_bootid[] is 4-byte 
> aligned, and then you can do
> 
> 	sprintf("%08x-%04x-%04x-%04x-%04x%08x",
> 		ntohl(0[(u32 *)uuid]),
> 		ntohs(2[(u16 *)uuid]),
> 		ntohs(3[(u16 *)uuid]),
> 		ntohs(4[(u16 *)uuid]),
> 		ntohs(5[(u16 *)uuid]),
> 		ntohl(3[(u32 *)uuid]));
> 
> which also gets bonus points for being totally unreadable, and thus 100% 
> in the spirit of uuid's.

again.. this is for compatibility with /proc/sys/kernel/random/boot_id .. the code 10 lines below my patch is identical and does
the %02x stuff... I didn't make that up, I just copied that to get the same output.
I can deviate for cleanup... but I can see some value of being the same format and same data.


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