[PATCH v3 1/4] block: Add trivial backing_fmt support to qcow, sheepdog, vmdk

[Eric Blake <eblake@redhat.com>]

For qcow2 and qed, we want to encourage the use of -F always, as these
formats can suffer from data corruption or security holes if backing
format is probed.  But for other formats, the backing format cannot be
recorded.  Making the user decide on a per-format basis whether to
supply a backing format string is awkward, better is to just blindly
accept a backing format argument even if it is ignored by the
contraints of the format at hand.

Signed-off-by: Eric Blake <eblake@redhat.com>
---
 block/qcow.c     | 6 ++++++
 block/sheepdog.c | 6 ++++++
 block/vmdk.c     | 5 +++++
 3 files changed, 17 insertions(+)

diff --git a/block/qcow.c b/block/qcow.c
index fce89898681f..d05c3d526170 100644
--- a/block/qcow.c
+++ b/block/qcow.c
@@ -947,6 +947,7 @@ static int coroutine_fn qcow_co_create_opts(const char *filename,

     static const QDictRenames opt_renames[] = {
         { BLOCK_OPT_BACKING_FILE,       "backing-file" },
+        { BLOCK_OPT_BACKING_FMT,        "backing-fmt" },
         { BLOCK_OPT_ENCRYPT,            BLOCK_OPT_ENCRYPT_FORMAT },
         { NULL, NULL },
     };
@@ -1151,6 +1152,11 @@ static QemuOptsList qcow_create_opts = {
             .type = QEMU_OPT_STRING,
             .help = "File name of a base image"
         },
+        {
+            .name = BLOCK_OPT_BACKING_FMT,
+            .type = QEMU_OPT_STRING,
+            .help = "Ignored (use raw backing files with caution)",
+        },
         {
             .name = BLOCK_OPT_ENCRYPT,
             .type = QEMU_OPT_BOOL,
diff --git a/block/sheepdog.c b/block/sheepdog.c
index cfa84338a2d6..248dcf4dfa01 100644
--- a/block/sheepdog.c
+++ b/block/sheepdog.c
@@ -2187,6 +2187,7 @@ static int coroutine_fn sd_co_create_opts(const char *filename, QemuOpts *opts,
     /* Change legacy command line options into QMP ones */
     static const QDictRenames opt_renames[] = {
         { BLOCK_OPT_BACKING_FILE,       "backing-file" },
+        { BLOCK_OPT_BACKING_FMT,        "backing-fmt" },
         { BLOCK_OPT_OBJECT_SIZE,        "object-size" },
         { NULL, NULL },
     };
@@ -3189,6 +3190,11 @@ static QemuOptsList sd_create_opts = {
             .type = QEMU_OPT_STRING,
             .help = "File name of a base image"
         },
+        {
+            .name = BLOCK_OPT_BACKING_FMT,
+            .type = QEMU_OPT_STRING,
+            .help = "Ignored (use raw backing files with caution)",
+        },
         {
             .name = BLOCK_OPT_PREALLOC,
             .type = QEMU_OPT_STRING,
diff --git a/block/vmdk.c b/block/vmdk.c
index 20e909d99794..53f3d864f3fe 100644
--- a/block/vmdk.c
+++ b/block/vmdk.c
@@ -3005,6 +3005,11 @@ static QemuOptsList vmdk_create_opts = {
             .type = QEMU_OPT_STRING,
             .help = "File name of a base image"
         },
+        {
+            .name = BLOCK_OPT_BACKING_FMT,
+            .type = QEMU_OPT_STRING,
+            .help = "Ignored (base image must be vmdk format)",
+        },
         {
             .name = BLOCK_OPT_COMPAT6,
             .type = QEMU_OPT_BOOL,
-- 
2.25.1