Re: [Qemu-devel] [PATCH] Align file accesses with cache=off (O_DIRECT)

[Laurent Vivier <Laurent.Vivier@bull.net>]

Le mardi 06 mai 2008 à 10:44 +0200, Kevin Wolf a écrit :
> Kevin Wolf schrieb:
> > Am Donnerstag, 1. Mai 2008 16:35:51 schrieb Blue Swirl:
> >> On 5/1/08, Kevin Wolf <mail@kevin-wolf.de> wrote:
> >>> Am Mittwoch, 30. April 2008 16:30:27 schrieb Blue Swirl:
> >>>> Maybe the alignment could be handled like AIO and synchronous IO
> >>>>
> >>>  > emulation layers are added in bdrv_register, but at open stage?
> >>>
> >>> You mean to preserve the original pread if the file is opened without
> >>> O_DIRECT and replace it by the emulation function only if O_DIRECT is
> >>> really used?
> >> Right.
> >>
> >> Maybe it's slightly faster that way and it would be closer to how
> >> other block emulations are handled. It's just an idea.
> > 
> > Maybe I'm missing something but AFAIK this pread pointer exists once for each 
> > block driver, i.e. every raw image uses the original pread or every raw image 
> > uses the emulating one. The difference between the O_DIRECT case and the 
> > AIO/sync emulation is that AIO/sync is the same for all devices of one driver 
> > while O_DIRECT can differ between images of the same driver.
> > 
> > So you would need to have one common pread which in turn calls a function 
> > pointer stored in the BlockDriverState. I doubt that this is much cheaper 
> > than an if in pread. And it wouldn't get too close to other emulations anyway 
> > because of the driver/device difference.
> 
> Should I change the patch now (even if I think it doesn't help anything) 
> or will you apply the patch as it is? It is quite frustrating to get no 
> answer at all.

Well, what is missing to Qemu is a MAINTAINERs list...

Fabrice, did you define sometime who can submit code in the repository
and on which part ? Perhaps you could write this in a "MAINTAINERS"
file ?
So we can CC: the maintainer when we have code to submit.

As I'm relatively new here, perhaps it is already existing or defined...

Regards, 
Laurent

-- 
------------- Laurent.Vivier@bull.net ---------------
"The best way to predict the future is to invent it."
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