[Qemu-devel] [PATCHv2] add qemu-img convert -C option (skip target volume creation)

[Alex Bligh <alex@alex.org.uk>]

Add a -C option to skip volume creation on qemu-img convert.
This is useful for targets such as rbd / ceph, where the
target volume may already exist; we cannot always rely on
qemu-img convert to create the image, as dependent on the
output format, there may be parameters which are not possible
to specify through the qemu-img convert command line.

Code:

Author: Alexandre Derumier <aderumier@odiso.com>
Signed-off-by: Alexandre Derumier <aderumier@odiso.com>
Signed-off-by: Alex Bligh <alex@alex.org.uk>

Documentaton:

Author: Alex Bligh <alex@alex.org.uk>
Signed-off-by: Alex Bligh <alex@alex.org.uk>
---
 qemu-img-cmds.hx |    4 ++--
 qemu-img.c       |   39 ++++++++++++++++++++++++---------------
 qemu-img.texi    |   15 ++++++++++++++-
 3 files changed, 40 insertions(+), 18 deletions(-)

diff --git a/qemu-img-cmds.hx b/qemu-img-cmds.hx
index 4ca7e95..74ced81 100644
--- a/qemu-img-cmds.hx
+++ b/qemu-img-cmds.hx
@@ -34,9 +34,9 @@ STEXI
 ETEXI
 
 DEF("convert", img_convert,
-    "convert [-c] [-p] [-q] [-f fmt] [-t cache] [-O output_fmt] [-o options] [-s snapshot_name] [-S sparse_size] filename [filename2 [...]] output_filename")
+    "convert [-c] [-p] [-q] [-C] [-f fmt] [-t cache] [-O output_fmt] [-o options] [-s snapshot_name] [-S sparse_size] filename [filename2 [...]] output_filename")
 STEXI
-@item convert [-c] [-p] [-q] [-f @var{fmt}] [-t @var{cache}] [-O @var{output_fmt}] [-o @var{options}] [-s @var{snapshot_name}] [-S @var{sparse_size}] @var{filename} [@var{filename2} [...]] @var{output_filename}
+@item convert [-c] [-p] [-q] [-C] [-f @var{fmt}] [-t @var{cache}] [-O @var{output_fmt}] [-o @var{options}] [-s @var{snapshot_name}] [-S @var{sparse_size}] @var{filename} [@var{filename2} [...]] @var{output_filename}
 ETEXI
 
 DEF("info", img_info,
diff --git a/qemu-img.c b/qemu-img.c
index b9a848d..c6e1cc0 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -103,6 +103,8 @@ static void help(void)
            "  '-S' indicates the consecutive number of bytes that must contain only zeros\n"
            "       for qemu-img to create a sparse image during conversion\n"
            "  '--output' takes the format in which the output must be done (human or json)\n"
+           "  '-C' skips the target volume creation (useful if the volume is created)\n"
+           "       prior to running qemu-img)\n"
            "\n"
            "Parameters to check subcommand:\n"
            "  '-r' tries to repair any inconsistencies that are found during the check.\n"
@@ -1116,7 +1118,8 @@ out3:
 
 static int img_convert(int argc, char **argv)
 {
-    int c, ret = 0, n, n1, bs_n, bs_i, compress, cluster_size, cluster_sectors;
+    int c, ret = 0, n, n1, bs_n, bs_i, compress, cluster_size,
+        cluster_sectors, skipcreate;
     int progress = 0, flags;
     const char *fmt, *out_fmt, *cache, *out_baseimg, *out_filename;
     BlockDriver *drv, *proto_drv;
@@ -1139,8 +1142,9 @@ static int img_convert(int argc, char **argv)
     cache = "unsafe";
     out_baseimg = NULL;
     compress = 0;
+    skipcreate = 0;
     for(;;) {
-        c = getopt(argc, argv, "f:O:B:s:hce6o:pS:t:q");
+        c = getopt(argc, argv, "f:O:B:s:hce6o:pS:t:qC");
         if (c == -1) {
             break;
         }
@@ -1161,6 +1165,9 @@ static int img_convert(int argc, char **argv)
         case 'c':
             compress = 1;
             break;
+        case 'C':
+            skipcreate = 1;
+            break;
         case 'e':
             error_report("option -e is deprecated, please use \'-o "
                   "encryption\' instead!");
@@ -1329,20 +1336,22 @@ static int img_convert(int argc, char **argv)
         }
     }
 
-    /* Create the new image */
-    ret = bdrv_create(drv, out_filename, param);
-    if (ret < 0) {
-        if (ret == -ENOTSUP) {
-            error_report("Formatting not supported for file format '%s'",
-                         out_fmt);
-        } else if (ret == -EFBIG) {
-            error_report("The image size is too large for file format '%s'",
-                         out_fmt);
-        } else {
-            error_report("%s: error while converting %s: %s",
-                         out_filename, out_fmt, strerror(-ret));
+    if (!skipcreate) {
+        /* Create the new image */
+        ret = bdrv_create(drv, out_filename, param);
+        if (ret < 0) {
+            if (ret == -ENOTSUP) {
+                error_report("Formatting not supported for file format '%s'",
+                             out_fmt);
+            } else if (ret == -EFBIG) {
+                error_report("The image size is too large for file format '%s'",
+                             out_fmt);
+            } else {
+                error_report("%s: error while converting %s: %s",
+                             out_filename, out_fmt, strerror(-ret));
+            }
+            goto out;
         }
-        goto out;
     }
 
     flags = BDRV_O_RDWR;
diff --git a/qemu-img.texi b/qemu-img.texi
index 69f1bda..9e5ba36 100644
--- a/qemu-img.texi
+++ b/qemu-img.texi
@@ -96,6 +96,14 @@ Second image format
 Strict mode - fail on on different image size or sector allocation
 @end table
 
+Parameters to convert subcommand:
+
+@table @option
+
+@item -C
+Skip the creation of the target volume
+@end table
+
 Command description:
 
 @table @option
@@ -171,7 +179,7 @@ Error on reading data
 
 @end table
 
-@item convert [-c] [-p] [-f @var{fmt}] [-t @var{cache}] [-O @var{output_fmt}] [-o @var{options}] [-s @var{snapshot_name}] [-S @var{sparse_size}] @var{filename} [@var{filename2} [...]] @var{output_filename}
+@item convert [-c] [-p] [-C] [-f @var{fmt}] [-t @var{cache}] [-O @var{output_fmt}] [-o @var{options}] [-s @var{snapshot_name}] [-S @var{sparse_size}] @var{filename} [@var{filename2} [...]] @var{output_filename}
 
 Convert the disk image @var{filename} or a snapshot @var{snapshot_name} to disk image @var{output_filename}
 using format @var{output_fmt}. It can be optionally compressed (@code{-c}
@@ -190,6 +198,11 @@ created as a copy on write image of the specified base image; the
 @var{backing_file} should have the same content as the input's base image,
 however the path, image format, etc may differ.
 
+If the @code{-C} option is specified, the target volume creation will be
+skipped. This is useful for formats such as @code{rbd} if the target
+volume has already been created with site specific options that cannot
+be supplied through qemu-img.
+
 @item info [-f @var{fmt}] [--output=@var{ofmt}] [--backing-chain] @var{filename}
 
 Give information about the disk image @var{filename}. Use it in
-- 
1.7.9.5