Re: [Qemu-devel] [PATCH 3/5] push down vector linearization to posix-aio-compat.c

[Anthony Liguori <anthony@codemonkey.ws>]

Christoph Hellwig wrote:
> Make all AIO requests vectored and defer linearization until the actual
> I/O thread.  This prepares for using native preadv/pwritev.
>
> Also enables asynchronous direct I/O by handling that case in the I/O thread.
>
> Win32 support is untested and uncompiled.  Then again I can't even find
> a know to turn on win32 aio support.
>   

It compiles for win32 but it breaks at this patch.  Win32 doesn't 
actually support AIO.  The code that's in #ifdefs has been dead for a 
long time.  I just committed a patch to remove it to avoid future 
confusion.  For the future, you can build/test win32 entirely in fedora 
by using the mingw32 packages and wine.

This bug is not limited to win32 though.  It has to do with having a 
backend disk format that does not provide a proper aio implement (which 
suggests your new brv_aio_{readv,writev}_em at fault).  You can 
reproduce on a normal Linux build by converting an existing image to a 
format like vmdk and then testing with that.  It's not 100% reliable but 
9 times out of 10 I don't get past the grub loader with this patch applied.

Regards,

Anthony Liguori

> Qcow and qcow2 propably want to be adopted to directly deal with multi-segment
> requests, but that can be implemented later.
>
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
>