[Qemu-devel] [PATCH v9 10/14] qemu-img: Specify backing file for commit

[Max Reitz <mreitz@redhat.com>]

Introduce a new parameter for qemu-img commit which may be used to
explicitly specify the backing file into which an image should be
committed if the backing chain has more than a single layer.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
---
 qemu-img-cmds.hx |  4 ++--
 qemu-img.c       | 24 +++++++++++++++++-------
 qemu-img.texi    |  9 ++++++++-
 3 files changed, 27 insertions(+), 10 deletions(-)

diff --git a/qemu-img-cmds.hx b/qemu-img-cmds.hx
index ea41d4f..4331949 100644
--- a/qemu-img-cmds.hx
+++ b/qemu-img-cmds.hx
@@ -22,9 +22,9 @@ STEXI
 ETEXI
 
 DEF("commit", img_commit,
-    "commit [-q] [-f fmt] [-t cache] [-d] [-p] filename")
+    "commit [-q] [-f fmt] [-t cache] [-b base] [-d] [-p] filename")
 STEXI
-@item commit [-q] [-f @var{fmt}] [-t @var{cache}] [-d] [-p] @var{filename}
+@item commit [-q] [-f @var{fmt}] [-t @var{cache}] [-b @var{base}] [-d] [-p] @var{filename}
 ETEXI
 
 DEF("compare", img_compare,
diff --git a/qemu-img.c b/qemu-img.c
index 8409062..daf4bba 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -759,7 +759,7 @@ static void run_block_job(BlockJob *job, Error **errp)
 static int img_commit(int argc, char **argv)
 {
     int c, ret, flags;
-    const char *filename, *fmt, *cache;
+    const char *filename, *fmt, *cache, *base;
     BlockDriverState *bs, *base_bs;
     bool progress = false, quiet = false, drop = false;
     Error *local_err = NULL;
@@ -767,8 +767,9 @@ static int img_commit(int argc, char **argv)
 
     fmt = NULL;
     cache = BDRV_DEFAULT_CACHE;
+    base = NULL;
     for(;;) {
-        c = getopt(argc, argv, "f:ht:dpq");
+        c = getopt(argc, argv, "f:ht:b:dpq");
         if (c == -1) {
             break;
         }
@@ -783,6 +784,11 @@ static int img_commit(int argc, char **argv)
         case 't':
             cache = optarg;
             break;
+        case 'b':
+            base = optarg;
+            /* -b implies -d */
+            drop = true;
+            break;
         case 'd':
             drop = true;
             break;
@@ -820,12 +826,16 @@ static int img_commit(int argc, char **argv)
     qemu_progress_init(progress, 1.f);
     qemu_progress_print(0.f, 100);
 
-    /* This is different from QMP, which by default uses the deepest file in the
-     * backing chain (i.e., the very base); however, the traditional behavior of
-     * qemu-img commit is using the immediate backing file. */
-    base_bs = bs->backing_hd;
+    if (base) {
+        base_bs = bdrv_find_backing_image(bs, base);
+    } else {
+        /* This is different from QMP, which by default uses the deepest file in
+         * the backing chain (i.e., the very base); however, the traditional
+         * behavior of qemu-img commit is using the immediate backing file. */
+        base_bs = bs->backing_hd;
+    }
     if (!base_bs) {
-        error_set(&local_err, QERR_BASE_NOT_FOUND, "NULL");
+        error_set(&local_err, QERR_BASE_NOT_FOUND, base ?: "NULL");
         goto done;
     }
 
diff --git a/qemu-img.texi b/qemu-img.texi
index 5c151af..04b6c9e 100644
--- a/qemu-img.texi
+++ b/qemu-img.texi
@@ -163,7 +163,7 @@ this case. @var{backing_file} will never be modified unless you use the
 The size can also be specified using the @var{size} option with @code{-o},
 it doesn't need to be specified separately in this case.
 
-@item commit [-q] [-f @var{fmt}] [-t @var{cache}] [-d] [-p] @var{filename}
+@item commit [-q] [-f @var{fmt}] [-t @var{cache}] [-b @var{base}] [-d] [-p] @var{filename}
 
 Commit the changes recorded in @var{filename} in its base image or backing file.
 If the backing file is smaller than the snapshot, then the backing file will be
@@ -176,6 +176,13 @@ The image @var{filename} is emptied after the operation has succeeded. If you do
 not need @var{filename} afterwards and intend to drop it, you may skip emptying
 @var{filename} by specifying the @code{-d} flag.
 
+If the backing chain of the given image file @var{filename} has more than one
+layer, the backing file into which the changes will be committed may be
+specified as @var{base} (which has to be part of @var{filename}'s backing
+chain). If @var{base} is not specified, the immediate backing file of the top
+image (which is @var{filename}) will be used. For reasons of consistency,
+explicitly specifying @var{base} will always imply @code{-d}.
+
 @item compare [-f @var{fmt}] [-F @var{fmt}] [-p] [-s] [-q] @var{filename1} @var{filename2}
 
 Check if two images have the same content. You can compare images with
-- 
2.0.1