Re: [Qemu-devel] [PULL] xen patches

[Stefano Stabellini]

Anthony,
please ignore this pull request, I'll rework and resubmit later.


On Wed, 25 Apr 2012, Christoph Hellwig wrote:
> On Tue, Apr 24, 2012 at 12:28:35PM +0100, Stefano Stabellini wrote:
> >       xen_disk: use bdrv_aio_flush instead of bdrv_flush
> 
> This one seems completely broken, as it just queues up the flushes and
> writes without any ordering between them.  Linux filesystems absolutely
> rely on a REQ_FUA request which gets mapped to BLKIF_OP_FLUSH_DISKCACHE
> to flush the data it actually sent.
> 
> I'm not sure who actually expects the preflush, but the only point
> in ever doing it would be to sequence it properly vs the write.

I see.. I need to make sure that the bdrv_aio_flush is fully completed
before issuing any reads or writes, not just ordered correctly: calling
bdrv_aio_flush before bdrv_aio_readv/writev is not enough.