On Wed, 2012-11-21 at 10:15 +0100, Kevin Wolf wrote: > Am 21.11.2012 09:58, schrieb Christian Borntraeger: > > From: Heinz Graalfs <graa...@linux.vnet.ibm.com> > > > > While testing IPL code (booting) for s390x we faced some problems > > with cache=none on dasds (4k block size) on bdrv_preads with length > > values != block size. > > > > This patch makes sure that bdrv_pread and friends work fine with > > unaligned access even with cache=none > > - propagate alignment value also into bs->file struct > > - modify the size in case of no cache to avoid EINVAL on > > pread() etc. (file was opened with O_DIRECT). > > > > This patch seems to cure the problems. > > > > CC: Kevin Wolf <kw...@redhat.com> > > CC: Stefan Hajnoczi <stefa...@redhat.com> > > Signed-off-by: Heinz Graalfs <graa...@linux.vnet.ibm.com> > > Signed-off-by: Christian Borntraeger <borntrae...@de.ibm.com> > > --- > > block.c | 3 +++ > > block/raw-posix.c | 6 ++++++ > > 2 files changed, 9 insertions(+) > > > > diff --git a/block.c b/block.c > > index 854ebd6..f23c562 100644 > > --- a/block.c > > +++ b/block.c > > @@ -4242,6 +4242,9 @@ BlockDriverAIOCB *bdrv_aio_ioctl(BlockDriverState *bs, > > void bdrv_set_buffer_alignment(BlockDriverState *bs, int align) > > { > > bs->buffer_alignment = align; > > + if ((bs->open_flags & BDRV_O_NOCACHE)) { > > + bs->file->buffer_alignment = align; > > + } > > Any reason to restrict this to BDRV_O_NOCACHE? > > There have been patches to change the BDRV_O_NOCACHE flag from the > monitor, in which case bdrv_set_buffer_alignment() wouldn't be called > anew and O_DIRECT requests start to fail again. >
OK > > } > > > > void *qemu_blockalign(BlockDriverState *bs, size_t size) > > diff --git a/block/raw-posix.c b/block/raw-posix.c > > index f2f0404..baebf1d 100644 > > --- a/block/raw-posix.c > > +++ b/block/raw-posix.c > > @@ -700,6 +700,12 @@ static BlockDriverAIOCB *paio_submit(BlockDriverState > > *bs, int fd, > > acb->aio_nbytes = nb_sectors * 512; > > acb->aio_offset = sector_num * 512; > > > > + /* O_DIRECT also requires an aligned length */ > > + if (bs->open_flags & BDRV_O_NOCACHE) { > > + acb->aio_nbytes += acb->bs->buffer_alignment - 1; > > + acb->aio_nbytes &= ~(acb->bs->buffer_alignment - 1); > > + } > > Modifying aio_nbytes, but not the iov looks wrong to me. This may work > in the handle_aiocb_rw_linear() code path, but not with actual vectored I/O. > Current coding ensures that read IO buffers always seem to be aligned correctly. Whereas read length values are not always appropriate for an O_DIRECT scenario. For a 2048 formatted disk I verified that 1. non vectored IO - the length needs to be adapted several times, which is accomplished now by the patch. 2. vectored IO - the qiov's total length is always a multiple of the logical block size (which is also verified in virtio_blk_handle_read()) The particular iov length fields are already correctly setup as a multiple of the logical block size when processed in virtio_blk_handle_request(). > Kevin >