[Qemu-devel] [PATCH 18/32] block: add bdrv_open_backing_file

[Kevin Wolf <kwolf@redhat.com>]

From: Paolo Bonzini <pbonzini@redhat.com>

Mirroring runs without the backing file so that it can be copied outside
QEMU.  However, we need to add it at the time the job is completed and
QEMU switches to the target.  Factor out the common bits of opening an
image and completing a mirroring operation.

The new function does not assume that the file is closed immediately after
it returns failure, so it keeps the BDRV_O_NO_BACKING flag up-to-date.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block.c |   56 ++++++++++++++++++++++++++++++++++++++------------------
 block.h |    1 +
 2 files changed, 39 insertions(+), 18 deletions(-)

diff --git a/block.c b/block.c
index a723be2..e06d78f 100644
--- a/block.c
+++ b/block.c
@@ -736,6 +736,42 @@ int bdrv_file_open(BlockDriverState **pbs, const char *filename, int flags)
     return 0;
 }
 
+int bdrv_open_backing_file(BlockDriverState *bs)
+{
+    char backing_filename[PATH_MAX];
+    int back_flags, ret;
+    BlockDriver *back_drv = NULL;
+
+    if (bs->backing_hd != NULL) {
+        return 0;
+    }
+
+    bs->open_flags &= ~BDRV_O_NO_BACKING;
+    if (bs->backing_file[0] == '\0') {
+        return 0;
+    }
+
+    bs->backing_hd = bdrv_new("");
+    bdrv_get_full_backing_filename(bs, backing_filename,
+                                   sizeof(backing_filename));
+
+    if (bs->backing_format[0] != '\0') {
+        back_drv = bdrv_find_format(bs->backing_format);
+    }
+
+    /* backing files always opened read-only */
+    back_flags = bs->open_flags & ~(BDRV_O_RDWR | BDRV_O_SNAPSHOT);
+
+    ret = bdrv_open(bs->backing_hd, backing_filename, back_flags, back_drv);
+    if (ret < 0) {
+        bdrv_delete(bs->backing_hd);
+        bs->backing_hd = NULL;
+        bs->open_flags |= BDRV_O_NO_BACKING;
+        return ret;
+    }
+    return 0;
+}
+
 /*
  * Opens a disk image (raw, qcow2, vmdk, ...)
  */
@@ -823,24 +859,8 @@ int bdrv_open(BlockDriverState *bs, const char *filename, int flags,
     }
 
     /* If there is a backing file, use it */
-    if ((flags & BDRV_O_NO_BACKING) == 0 && bs->backing_file[0] != '\0') {
-        char backing_filename[PATH_MAX];
-        int back_flags;
-        BlockDriver *back_drv = NULL;
-
-        bs->backing_hd = bdrv_new("");
-        bdrv_get_full_backing_filename(bs, backing_filename,
-                                       sizeof(backing_filename));
-
-        if (bs->backing_format[0] != '\0') {
-            back_drv = bdrv_find_format(bs->backing_format);
-        }
-
-        /* backing files always opened read-only */
-        back_flags =
-            flags & ~(BDRV_O_RDWR | BDRV_O_SNAPSHOT | BDRV_O_NO_BACKING);
-
-        ret = bdrv_open(bs->backing_hd, backing_filename, back_flags, back_drv);
+    if ((flags & BDRV_O_NO_BACKING) == 0) {
+        ret = bdrv_open_backing_file(bs);
         if (ret < 0) {
             bdrv_close(bs);
             return ret;
diff --git a/block.h b/block.h
index ed4b90d..096fa09 100644
--- a/block.h
+++ b/block.h
@@ -133,6 +133,7 @@ void bdrv_append(BlockDriverState *bs_new, BlockDriverState *bs_top);
 void bdrv_delete(BlockDriverState *bs);
 int bdrv_parse_cache_flags(const char *mode, int *flags);
 int bdrv_file_open(BlockDriverState **pbs, const char *filename, int flags);
+int bdrv_open_backing_file(BlockDriverState *bs);
 int bdrv_open(BlockDriverState *bs, const char *filename, int flags,
               BlockDriver *drv);
 BlockReopenQueue *bdrv_reopen_queue(BlockReopenQueue *bs_queue,
-- 
1.7.6.5