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authorKevin Wolf <kwolf@redhat.com>2013-11-28 10:23:32 +0100
committerKevin Wolf <kwolf@redhat.com>2014-01-24 17:40:01 +0100
commit339064d5063924e5176842abbf6c8089f3479c5b (patch)
tree5569f25292a2b166cf19e33ce73f1c5de2d21760 /include
parent1ff735bdc417945bc6df1857861b127644b3f461 (diff)
block: Don't use guest sector size for qemu_blockalign()
bs->buffer_alignment is set by the device emulation and contains the logical block size of the guest device. This isn't something that the block layer should know, and even less something to use for determining the right alignment of buffers to be used for the host. The new BlockLimits field opt_mem_alignment tells the qemu block layer the optimal alignment to be used so that no bounce buffer must be used in the driver. This patch may change the buffer alignment from 4k to 512 for all callers that used qemu_blockalign() with the top-level image format BlockDriverState. The value was never propagated to other levels in the tree, so in particular raw-posix never required anything else than 512. While on disks with 4k sectors direct I/O requires a 4k alignment, memory may still be okay when aligned to 512 byte boundaries. This is what must have happened in practice, because otherwise this would already have failed earlier. Therefore I don't expect regressions even with this intermediate state. Later, raw-posix can implement the hook and expose a different memory alignment requirement. Signed-off-by: Kevin Wolf <kwolf@redhat.com> Reviewed-by: Wenchao Xia <xiawenc@linux.vnet.ibm.com> Reviewed-by: Max Reitz <mreitz@redhat.com>
Diffstat (limited to 'include')
-rw-r--r--include/block/block.h3
-rw-r--r--include/block/block_int.h3
2 files changed, 6 insertions, 0 deletions
diff --git a/include/block/block.h b/include/block/block.h
index 00a8790660..332ebb94fb 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -428,6 +428,9 @@ void bdrv_img_create(const char *filename, const char *fmt,
char *options, uint64_t img_size, int flags,
Error **errp, bool quiet);
+/* Returns the alignment in bytes that is required so that no bounce buffer
+ * is required throughout the stack */
+size_t bdrv_opt_mem_align(BlockDriverState *bs);
void bdrv_set_buffer_alignment(BlockDriverState *bs, int align);
void *qemu_blockalign(BlockDriverState *bs, size_t size);
bool bdrv_qiov_is_aligned(BlockDriverState *bs, QEMUIOVector *qiov);
diff --git a/include/block/block_int.h b/include/block/block_int.h
index f6fa1f6f36..74a78a6831 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -258,6 +258,9 @@ typedef struct BlockLimits {
/* optimal transfer length in sectors */
int opt_transfer_length;
+
+ /* memory alignment so that no bounce buffer is needed */
+ size_t opt_mem_alignment;
} BlockLimits;
/*