block: Add driver-specific options for backing files

Options starting in "backing." are passed to the backing file now. If
you don't need to specify the filename for the backing file, you can add
it on the command line instead of in the image file:

$ qemu-nbd -t /tmp/test.img
$ qemu-img create -f qcow2 empty.qcow2 1G
$ qemu-system-x86_64 -drive file=empty.qcow2,backing.file.driver=nbd,\
    backing.file.host=localhost

Note that this doesn't override the backing filename from the image. If
the image has one, this will fail because NBD doesn't want the options
and a filename at the same time.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>

diff --git a/block.c b/block.c
index bea47c47555dcec297193d6e2ccc6e05d2f795ed..f717e1aedccab018681e8cd22eabdd31a70a30b5 100644 (file)
--- a/block.c
+++ b/block.c
@@ -845,18 +845,33 @@ fail:
     return ret;
 }
 
-int bdrv_open_backing_file(BlockDriverState *bs)
+/*
+ * Opens the backing file for a BlockDriverState if not yet open
+ *
+ * options is a QDict of options to pass to the block drivers, or NULL for an
+ * empty set of options. The reference to the QDict is transferred to this
+ * function (even on failure), so if the caller intends to reuse the dictionary,
+ * it needs to use QINCREF() before calling bdrv_file_open.
+ */
+int bdrv_open_backing_file(BlockDriverState *bs, QDict *options)
 {
     char backing_filename[PATH_MAX];
     int back_flags, ret;
     BlockDriver *back_drv = NULL;
 
     if (bs->backing_hd != NULL) {
+        QDECREF(options);
         return 0;
     }
 
+    /* NULL means an empty set of options */
+    if (options == NULL) {
+        options = qdict_new();
+    }
+
     bs->open_flags &= ~BDRV_O_NO_BACKING;
-    if (bs->backing_file[0] == '\0') {
+    if (bs->backing_file[0] == '\0' && qdict_size(options) == 0) {
+        QDECREF(options);
         return 0;
     }
 
@@ -871,7 +886,8 @@ int bdrv_open_backing_file(BlockDriverState *bs)
     /* 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, NULL,
+    ret = bdrv_open(bs->backing_hd,
+                    *backing_filename ? backing_filename : NULL, options,
                     back_flags, back_drv);
     if (ret < 0) {
         bdrv_delete(bs->backing_hd);
@@ -1027,7 +1043,10 @@ int bdrv_open(BlockDriverState *bs, const char *filename, QDict *options,
 
     /* If there is a backing file, use it */
     if ((flags & BDRV_O_NO_BACKING) == 0) {
-        ret = bdrv_open_backing_file(bs);
+        QDict *backing_options;
+
+        extract_subqdict(options, &backing_options, "backing.");
+        ret = bdrv_open_backing_file(bs, backing_options);
         if (ret < 0) {
             goto close_and_fail;
         }

diff --git a/block/mirror.c b/block/mirror.c
index a62ad86c28f7ce017d68dd42da3a71c2167d95de..8b07dec314812c77cc103e7158a6fb9e949d3480 100644 (file)
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -507,7 +507,7 @@ static void mirror_complete(BlockJob *job, Error **errp)
     MirrorBlockJob *s = container_of(job, MirrorBlockJob, common);
     int ret;
 
-    ret = bdrv_open_backing_file(s->target);
+    ret = bdrv_open_backing_file(s->target, NULL);
     if (ret < 0) {
         char backing_filename[PATH_MAX];
         bdrv_get_full_backing_filename(s->target, backing_filename,

diff --git a/include/block/block.h b/include/block/block.h
index ebd95127a1fe28b739f4037434ac58260cbfdf72..1251c5cf9f8f136704334cd35387d18e87844c47 100644 (file)
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -137,7 +137,7 @@ int bdrv_parse_cache_flags(const char *mode, int *flags);
 int bdrv_parse_discard_flags(const char *mode, int *flags);
 int bdrv_file_open(BlockDriverState **pbs, const char *filename,
                    QDict *options, int flags);
-int bdrv_open_backing_file(BlockDriverState *bs);
+int bdrv_open_backing_file(BlockDriverState *bs, QDict *options);
 int bdrv_open(BlockDriverState *bs, const char *filename, QDict *options,
               int flags, BlockDriver *drv);
 BlockReopenQueue *bdrv_reopen_queue(BlockReopenQueue *bs_queue,