linux-kernel - Re: [PATCH 6/10] lguest code: the little linux hypervisor.

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Message-ID: <45CC5771.1070309@vmware.com>
Date:	Fri, 09 Feb 2007 03:13:53 -0800
From:	Zachary Amsden <zach@...are.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	lkml - Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andi Kleen <ak@....de>,
	virtualization <virtualization@...ts.osdl.org>,
	Paul Mackerras <paulus@...ba.org>,
	Stephen Rothwell <sfr@...b.auug.org.au>
Subject: Re: [PATCH 6/10] lguest code: the little linux hypervisor.

Rusty Russell wrote:
> On Fri, 2007-02-09 at 01:35 -0800, Andrew Morton wrote:
>   
>> On Fri, 09 Feb 2007 20:20:27 +1100 Rusty Russell <rusty@...tcorp.com.au> wrote:
>>
>>     
>>> +#define log(...)					\
>>> +	do {						\
>>> +		mm_segment_t oldfs = get_fs();		\
>>> +		char buf[100];				\
>>> +		sprintf(buf, "lguest:" __VA_ARGS__);	\
>>> +		set_fs(KERNEL_DS);			\
>>> +		sys_write(1, buf, strlen(buf));		\
>>> +		set_fs(oldfs);				\
>>> +	} while(0)
>>>       
>> Due to gcc shortcomings, each instance of this will chew an additional 100
>> bytes of stack.  Unless they fixed it recently.  Is a bit of a timebomb.  I
>> guess ksaprintf() could be used.
>>
>> It also looks a bit, umm, innovative.
>>     
>
> It's also unused 8)
>
> It's an extremely useful macro for doing grossly invasive logging of the
> guest.  I'll drop it if you prefer.
>   

Yes, it is a bit, umm, innovative.  If it is going to be kept, even if 
just for devel logging, you should disable interrupts around it.  
Changing segments is not a normal thing to do.

Zach
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