Re: [Qemu-devel] [4367] Align file accesses with cache=off (Kevin Wolf, Laurent Vivier)

[Anthony Liguori <anthony@codemonkey.ws>]

Fabrice Bellard wrote:
> A note: in order to avoid uncontrolled recursions, it is better to call
> the read/write AIO callback outside the aio_read/write (see
> bdrv_aio_read_em).
>
> Personally I would not trust the OS to correctly handle the mix of
> O_DIRECT and buffered operations, especially if the corresponding file
> regions intersect !
>   

Indeed, why not just allocate a temporary buffer and realign the access 
such that it's correct?  If that involves doing a read first then a 
write, so be it.

Messing with file flags is very dangerous as there may be a request 
in-flight already in a different thread.  I don't think this patch is 
safe at all.

Regards,

Anthony Liguori

> Fabrice.
>
> Blue Swirl wrote:
>   
>> Revision: 4367
>>           http://svn.sv.gnu.org/viewvc/?view=rev&root=qemu&revision=4367
>> Author:   blueswir1
>> Date:     2008-05-06 17:26:59 +0000 (Tue, 06 May 2008)
>>
>> Log Message:
>> -----------
>> Align file accesses with cache=off (Kevin Wolf, Laurent Vivier)
>>
>> Modified Paths:
>> --------------
>>     trunk/block-raw-posix.c
>> [...]
>>     
>
>
>