add qemu-img convert -n option (skip target volume creation)

Add a -n 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.

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Alexandre Derumier <aderumier@odiso.com>
Signed-off-by: Alex Bligh <alex@alex.org.uk>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

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] [-n] [-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] [-n] [-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,

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"
+           "  '-n' 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, skip_create;
     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;
+    skip_create = 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:qn");
         if (c == -1) {
             break;
         }
@@ -1197,6 +1201,9 @@ static int img_convert(int argc, char **argv)
         case 'q':
             quiet = true;
             break;
+        case 'n':
+            skip_create = 1;
+            break;
         }
     }
 
@@ -1329,6 +1336,7 @@ static int img_convert(int argc, char **argv)
         }
     }
 
+    if (!skip_create) {
         /* Create the new image */
         ret = bdrv_create(drv, out_filename, param);
         if (ret < 0) {
@@ -1344,6 +1352,7 @@ static int img_convert(int argc, char **argv)
             }
             goto out;
         }
+    }
 
     flags = BDRV_O_RDWR;
     ret = bdrv_parse_cache_flags(cache, &flags);
@@ -1363,6 +1372,20 @@ static int img_convert(int argc, char **argv)
     bdrv_get_geometry(bs[0], &bs_sectors);
     buf = qemu_blockalign(out_bs, IO_BUF_SIZE);
 
+    if (skip_create) {
+        int64_t output_length = bdrv_getlength(out_bs);
+        if (output_length < 0) {
+            error_report("unable to get output image length: %s\n",
+                         strerror(-output_length));
+            ret = -1;
+            goto out;
+        } else if (output_length < total_sectors << BDRV_SECTOR_BITS) {
+            error_report("output file is smaller than input file");
+            ret = -1;
+            goto out;
+        }
+    }
+
     if (compress) {
         ret = bdrv_get_info(out_bs, &bdi);
         if (ret < 0) {

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 -n
+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] [-n] [-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{-n} 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

tests/qemu-iotests/063

@@ -0,0 +1,97 @@
+#!/bin/bash
+#
+# test of qemu-img convert -n - convert without creation
+#
+# Copyright (C) 2009 Red Hat, Inc.
+# Copyright (C) 2013 Alex Bligh (alex@alex.org.uk)
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+
+# creator
+owner=alex@alex.org.uk
+
+seq=`basename $0`
+echo "QA output created by $seq"
+
+here=`pwd`
+tmp=/tmp/$$
+status=1	# failure is the default!
+
+_cleanup()
+{
+	_cleanup_test_img
+	rm -f $TEST_IMG.orig $TEST_IMG.raw $TEST_IMG.raw2
+}
+trap "_cleanup; exit \$status" 0 1 2 3 15
+
+# get standard environment, filters and checks
+. ./common.rc
+. ./common.filter
+. ./common.pattern
+
+_supported_fmt qcow qcow2 vmdk qed raw
+_supported_proto generic
+_supported_os Linux
+
+_make_test_img 4M
+
+echo "== Testing conversion with -n fails with no target file =="
+# check .orig file does not exist
+rm -f $TEST_IMG.orig
+if $QEMU_IMG convert -f $IMGFMT -O $IMGFMT -n $TEST_IMG $TEST_IMG.orig >/dev/null 2>&1; then
+    exit 1
+fi
+
+echo "== Testing conversion with -n succeeds with a target file =="
+rm -f $TEST_IMG.orig
+cp $TEST_IMG $TEST_IMG.orig
+if ! $QEMU_IMG convert -f $IMGFMT -O $IMGFMT -n $TEST_IMG $TEST_IMG.orig ; then
+    exit 1
+fi
+
+echo "== Testing conversion to raw is the same after conversion with -n =="
+# compare the raw files
+if ! $QEMU_IMG convert -f $IMGFMT -O raw $TEST_IMG $TEST_IMG.raw1 ; then
+    exit 1
+fi
+
+if ! $QEMU_IMG convert -f $IMGFMT -O raw $TEST_IMG.orig $TEST_IMG.raw2 ; then
+    exit 1
+fi
+
+if ! cmp $TEST_IMG.raw1 $TEST_IMG.raw2 ; then
+    exit 1
+fi
+
+echo "== Testing conversion back to original format =="
+if ! $QEMU_IMG convert -f raw -O $IMGFMT -n $TEST_IMG.raw2 $TEST_IMG ; then
+    exit 1
+fi
+_check_test_img
+
+echo "== Testing conversion to a smaller file fails =="
+rm -f $TEST_IMG.orig
+mv $TEST_IMG $TEST_IMG.orig
+_make_test_img 2M
+if $QEMU_IMG convert -f $IMGFMT -O $IMGFMT -n $TEST_IMG.orig $TEST_IMG >/dev/null 2>&1; then
+    exit 1
+fi
+
+rm -f $TEST_IMG.orig $TEST_IMG.raw $TEST_IMG.raw2
+
+echo "*** done"
+rm -f $seq.full
+status=0
+exit 0

tests/qemu-iotests/063.out

@@ -0,0 +1,10 @@
+QA output created by 063
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=4194304
+== Testing conversion with -n fails with no target file ==
+== Testing conversion with -n succeeds with a target file ==
+== Testing conversion to raw is the same after conversion with -n ==
+== Testing conversion back to original format ==
+No errors were found on the image.
+== Testing conversion to a smaller file fails ==
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=2097152
+*** done

tests/qemu-iotests/group

@@ -66,3 +66,4 @@
 059 rw auto
 060 rw auto
 062 rw auto
+063 rw auto