[Qemu-devel] [RFC PATCH 27/36] block: add bdrv_ensure_backing_file

[Paolo Bonzini]

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.

Signed-off-by: Paolo Bonzini <address@hidden>
---
 block.c |   69 ++++++++++++++++++++++++++++++++++++++++-----------------------
 block.h |    1 +
 2 files changed, 45 insertions(+), 25 deletions(-)

diff --git a/block.c b/block.c
index dbb9041..5b08c5b 100644
--- a/block.c
+++ b/block.c
@@ -730,6 +730,48 @@ int bdrv_file_open(BlockDriverState **pbs, const char 
*filename, int flags)
     return 0;
 }
 
+int bdrv_ensure_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_close(bs);
+        bdrv_delete(bs->backing_hd);
+        bs->backing_hd = NULL;
+        return ret;
+    }
+    if (bs->is_temporary) {
+        bs->backing_hd->keep_read_only = !(bs->open_flags & BDRV_O_RDWR);
+    } else {
+        /* base images use the same setting as leaf */
+        bs->backing_hd->keep_read_only = bs->keep_read_only;
+    }
+    return 0;
+}
+
 /*
  * Opens a disk image (raw, qcow2, vmdk, ...)
  */
@@ -813,34 +855,11 @@ 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_ensure_backing_file(bs);
         if (ret < 0) {
-            bdrv_close(bs);
             return ret;
         }
-        if (bs->is_temporary) {
-            bs->backing_hd->keep_read_only = !(flags & BDRV_O_RDWR);
-        } else {
-            /* base image inherits from "parent" */
-            bs->backing_hd->keep_read_only = bs->keep_read_only;
-        }
     }
 
     if (!bdrv_key_required(bs)) {
diff --git a/block.h b/block.h
index c13d779..a4aea47 100644
--- a/block.h
+++ b/block.h
@@ -122,6 +122,7 @@ 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_ensure_backing_file(BlockDriverState *bs);
 int bdrv_open(BlockDriverState *bs, const char *filename, int flags,
               BlockDriver *drv);
 void bdrv_close(BlockDriverState *bs);
-- 
1.7.10.2