block: add BLOCK_O_CHECK for qemu-img check

Image formats with a dirty bit, like qed and qcow2, repair dirty image
files upon open with BDRV_O_RDWR.  Performing automatic repair when
qemu-img check runs is not ideal because the bdrv_open() call repairs
the image before the actual bdrv_check() call from qemu-img.c.

Fix this "double repair" since it leads to confusing output from
qemu-img check.  Tell the block driver that this image is being opened
just for bdrv_check().  This skips automatic repair and qemu-img.c can
invoke it manually with bdrv_check().

Update the golden output for qemu-iotests 039 to reflect the new
qemu-img check output.

Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block.h

@@ -79,6 +79,7 @@ typedef struct BlockDevOps {
 #define BDRV_O_NO_FLUSH    0x0200 /* disable flushing on this disk */
 #define BDRV_O_COPY_ON_READ 0x0400 /* copy read backing sectors into image */
 #define BDRV_O_INCOMING    0x0800  /* consistency hint for incoming migration */
+#define BDRV_O_CHECK       0x1000  /* open solely for consistency check */
 
 #define BDRV_O_CACHE_MASK  (BDRV_O_NOCACHE | BDRV_O_CACHE_WB | BDRV_O_NO_FLUSH)
 

block/qcow2.c

@@ -484,8 +484,8 @@ static int qcow2_open(BlockDriverState *bs, int flags)
     qemu_co_mutex_init(&s->lock);
 
     /* Repair image if dirty */
-    if ((s->incompatible_features & QCOW2_INCOMPAT_DIRTY) &&
-        !bs->read_only) {
+    if (!(flags & BDRV_O_CHECK) && !bs->read_only &&
+        (s->incompatible_features & QCOW2_INCOMPAT_DIRTY)) {
         BdrvCheckResult result = {0};
 
         ret = qcow2_check(bs, &result, BDRV_FIX_ERRORS);

block/qed.c

@@ -477,7 +477,7 @@ static int bdrv_qed_open(BlockDriverState *bs, int flags)
     }
 
     /* If image was not closed cleanly, check consistency */
-    if (s->header.features & QED_F_NEED_CHECK) {
+    if (!(flags & BDRV_O_CHECK) && (s->header.features & QED_F_NEED_CHECK)) {
         /* Read-only images cannot be fixed.  There is no risk of corruption
          * since write operations are not possible.  Therefore, allow
          * potentially inconsistent images to be opened read-only.  This can

qemu-img.c

@@ -379,7 +379,7 @@ static int img_check(int argc, char **argv)
     BlockDriverState *bs;
     BdrvCheckResult result;
     int fix = 0;
-    int flags = BDRV_O_FLAGS;
+    int flags = BDRV_O_FLAGS | BDRV_O_CHECK;
 
     fmt = NULL;
     for(;;) {

tests/qemu-iotests/039.out

@@ -26,6 +26,12 @@ incompatible_features     0x1
 == Repairing the image file must succeed ==
 ERROR OFLAG_COPIED: offset=8000000000050000 refcount=0
 Repairing cluster 5 refcount=0 reference=1
+The following inconsistencies were found and repaired:
+
+    0 leaked clusters
+    1 corruptions
+
+Double checking the fixed image now...
 No errors were found on the image.
 incompatible_features     0x0