[Qemu-devel] [PATCH/RFC] block: Ensure that block size constraints are considered

[Christian Borntraeger]

From: Heinz Graalfs <address@hidden>

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 <address@hidden>
CC: Stefan Hajnoczi <address@hidden>
Signed-off-by: Heinz Graalfs <address@hidden>
Signed-off-by: Christian Borntraeger <address@hidden>
---
 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;
+    }
 }
 
 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);
+    }
+
     trace_paio_submit(acb, opaque, sector_num, nb_sectors, type);
     return thread_pool_submit_aio(aio_worker, acb, cb, opaque);
 }
-- 
1.7.10.1