[Qemu-devel] [PATCH 2/4] block: Read only one sector for format probing

[Kevin Wolf <kwolf@redhat.com>]

The only image format driver that even potentially accesses anything
after 512 bytes in its bdrv_probe() implementation is VMDK, which reads
a plain-text descriptor file. In practice, the field it's looking for
seems to come first and will be well within the first 512 bytes, too.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block.c                   | 2 +-
 include/block/block_int.h | 2 ++
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/block.c b/block.c
index 8da6e61..8006685 100644
--- a/block.c
+++ b/block.c
@@ -678,7 +678,7 @@ static int find_image_format(BlockDriverState *bs, const char *filename,
                              BlockDriver **pdrv, Error **errp)
 {
     BlockDriver *drv;
-    uint8_t buf[2048];
+    uint8_t buf[BLOCK_PROBE_BUF_SIZE];
     int ret = 0;
 
     /* Return the raw BlockDriver * to scsi-generic devices or empty drives */
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 8898c6c..697cd5d 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -57,6 +57,8 @@
 #define BLOCK_OPT_REDUNDANCY        "redundancy"
 #define BLOCK_OPT_NOCOW             "nocow"
 
+#define BLOCK_PROBE_BUF_SIZE        512
+
 typedef struct BdrvTrackedRequest {
     BlockDriverState *bs;
     int64_t offset;
-- 
1.8.3.1