linux-kernel - Re: Top kernel oopses/warnings this week

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Date:	Mon, 17 Dec 2007 16:39:25 -0800
From:	Arjan van de Ven <arjan@...ux.intel.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Tony Luck <tony.luck@...el.com>, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>, protasnb@...il.com,
	tytso@...nk.org
Subject: Re: Top kernel oopses/warnings this week

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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