[Qemu-devel] Re: [PATCH][v2] Align file accesses with cache=off (O_DIRECT)

[Anthony Liguori <anthony@codemonkey.ws>]

Laurent Vivier wrote:
> This patch is the original patch from Kevin Wolf modified according
> comments given on the qemu-devel Mailing list.
>
> Original Description:
>
> "In December a patch was applied which introduced the cache=off option
> to -drive. When using this option files are opened with the O_DIRECT
> flag.
> This means that all accesses have to be aligned. The patch made a couple
> of changes in this respect, still in other places they are missing (e.g.
> you can't use cache=off with qcow(2) files).
>
> This patch implements wrappers for raw_pread and raw_pwrite which align
> all file accesses and make qcow(2) work with cache=off. This method
> might not be the most performant one (compared to fixing qcow, qcow2 and
> everything else that might be using unaligned accesses), but unaligned
> accesses don't happen that frequently and with this patch really all
> image accesses should be covered."
>
> Modifications:
>
> - Kevin has modified his patch to call the read/write AIO callback
> outside the aio_read/write
> - I've modified the buffer management to allocate buffer on open and not
> on each read/write.
>
> As mentioned by Kevin, this patch is really needed to be able to manage
> all disk images with "cache=off" option, so pleeeaaaase, apply (or
> comment...)
>
> A la GIT:
>
> Signed-off-by: Kevin Wolf <kwolf@suse.de>
> Signed-off-by: Laurent Vivier <Laurent.Vivier@bull.net>
>   

Looks better to me.

Acked-by: Anthony Liguori <aliguori@us.ibm.com>

Regads,

Anthony Liguori