Am 27.07.2010 21:04, schrieb Andrea Arcangeli: > Subject: avoid canceling ide dma > > From: Andrea Arcangeli <aarca...@redhat.com> > > The reason for not actually canceling the I/O is because with > virtualization and lots of VM running, a guest fs may mistake a > overload of the host, as an IDE timeout. So rather than canceling the > I/O, it's safer to wait I/O completion and simulate that the I/O has > completed just before the io cancellation was requested by the > guest. This way if ntfs or an app writes data without checking for > -EIO retval, and it thinks the write has succeeded, it's less likely > to run into troubles. Similar issues for reads. > > Furthermore because the DMA operation is splitted into many synchronous > aio_read/write if there's more than one entry in the SG table, without this > patch the DMA would be cancelled in the middle, something we've no idea if it > happens on real hardware too or not. Overall this seems a great risk for zero > gain. > > This approach is sure safer than previous code given we can't pretend all > guest > fs code out there to check for errors and reply the DMA if it was completed > partially, given a timeout would never materialize on a real harddisk unless > there are defective blocks (and defective blocks are practically only an issue > for reads never for writes in any recent hardware as writing to blocks is the > way to fix them) or the harddisk breaks as a whole. > > Signed-off-by: Izik Eidus <iei...@redhat.com> > Signed-off-by: Andrea Arcangeli <aarca...@redhat.com>
Thanks, applied to the block branch. Kevin
