On Wed, 2012-11-21 at 11:00 +0100, Christian Borntraeger wrote: > On 21/11/12 10:15, 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. > > > Right, should be ok to remove the check. > > > > > >> } > >> > >> 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. > > I think it seemed to work because the vectored I/O cases that we were testing > were properly > aligned or were in the QEMU_AIO_MISALIGNED case which does bounce buffering > anyway. > But I am not sure... > > Heinz can you have a look at this and identify the exact place were it was > failing > and why this patch helps? (I just know it does). That might help to > understand > if we also need to touch the iovs.
The pread() call in handle_aiocb_rw_linear() is failing with errno 22. At least for this path the patch ensures that the length is correctly set. I need to look into the vectored I/O part in more detail. > Christian > >