Re: [Qemu-devel] Re: [PATCH] block: fix sector comparism in multiwrite_req_compare

[Kevin Wolf]

Am 20.05.2010 08:09, schrieb Avi Kivity:
> On 05/20/2010 12:09 AM, Kevin Wolf wrote:
>>
>>> Actually it's not that obvious.  If the actual problem
>>> here (besides the mis-comparison) is due to missing
>>> barriers or flushes.  Avi asked a good question in that
>>> thread.
>>>      
>> It's obvious that it's a hack. It doesn't fix anything, it just disables a
>> feature that didn't work. Good for debugging, but not something that you
>> would like to commit.
>>
>> It's reasonable to include something like this when we know that something is
>> broken but we haven't found it yet - but I believe Christoph's patch is the
>> real fix. If anyone can still find a case that is "fixed" by Avi's patch, I
>> could be convinced to apply it anyway, but I'd prefer if I didn't have to.
>>
>> Note that we actually don't have overlapping requests. It just looks like it
>> because the qsort call doesn't work correctly with the broken comparison
>> function, so lower sector numbers can come after higher ones.
>>    
> 
> I agree my patch didn't fix the problem, only made it disappear, but 
> won't the current code break with overlapping requests?

Maybe --verbose for your patch descriptions would help. I didn't see any
obvious problem. If you know any, care to explain?

Anyway, I started to implement a multiwrite command for qemu-io
yesterday, so that I can actually test such scenarios.

Kevin