block: Introduce BDRV_O_NO_BACKING

If an image references a backing file that doesn't exist, qemu-img info fails
to open this image. Exactly in this case the info would be valuable, though:
the user might want to find out which file is missing.

This patch introduces a BDRV_O_NO_BACKING flag to ignore the backing file when
opening the image. qemu-img info is the first user and provides info now even
if the backing file is invalid.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

3 files changed, 4 insertions, 3 deletions

diff --git a/block.c b/block.c
index 30ae2b1e54..994109e0b9 100644
--- a/block.c
+++ b/block.c
@@ -477,7 +477,7 @@ int bdrv_open2(BlockDriverState *bs, const char *filename, int flags,
         unlink(filename);
     }
 #endif
-    if (bs->backing_file[0] != '\0') {
+    if ((flags & BDRV_O_NO_BACKING) == 0 && bs->backing_file[0] != '\0') {
         /* if there is a backing file, use it */
         BlockDriver *back_drv = NULL;
         bs->backing_hd = bdrv_new("");
@@ -1352,7 +1352,7 @@ const char *bdrv_get_encrypted_filename(BlockDriverState *bs)
 void bdrv_get_backing_filename(BlockDriverState *bs,
                                char *filename, int filename_size)
 {
-    if (!bs->backing_hd) {
+    if (!bs->backing_file) {
         pstrcpy(filename, filename_size, "");
     } else {
         pstrcpy(filename, filename_size, bs->backing_file);
diff --git a/block.h b/block.h
index fa51ddf150..f660d5f4d9 100644
--- a/block.h
+++ b/block.h
@@ -39,6 +39,7 @@ typedef struct QEMUSnapshotInfo {
 #define BDRV_O_NOCACHE     0x0020 /* do not use the host page cache */
 #define BDRV_O_CACHE_WB    0x0040 /* use write-back caching */
 #define BDRV_O_NATIVE_AIO  0x0080 /* use native AIO instead of the thread pool */
+#define BDRV_O_NO_BACKING  0x0100 /* don't open the backing file */
 
 #define BDRV_O_CACHE_MASK  (BDRV_O_NOCACHE | BDRV_O_CACHE_WB)
 
diff --git a/qemu-img.c b/qemu-img.c
index 1d97f2ebfb..5ad88bf763 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -884,7 +884,7 @@ static int img_info(int argc, char **argv)
     } else {
         drv = NULL;
     }
-    if (bdrv_open2(bs, filename, BRDV_O_FLAGS, drv) < 0) {
+    if (bdrv_open2(bs, filename, BRDV_O_FLAGS | BDRV_O_NO_BACKING, drv) < 0) {
         error("Could not open '%s'", filename);
     }
     bdrv_get_format(bs, fmt_name, sizeof(fmt_name));