qemu-img: Improve error for rebase without backing format

When removeing support for qemu-img being able to create backing
chains without embedded backing formats, we caused a poor error
message as caught by iotest 114.  Improve the situation to inform the
user what went wrong.

Suggested-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20210708155228.2666172-1-eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

diff --git a/qemu-img.c b/qemu-img.c
index ec0e2fabe54ae2bfef10d7c34269e1a7821c86b4..7c4fc60312b18ccd1433151ae5339849e4add5ac 100644 (file)
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -3767,6 +3767,9 @@ static int img_rebase(int argc, char **argv)
     if (ret == -ENOSPC) {
         error_report("Could not change the backing file to '%s': No "
                      "space left in the file header", out_baseimg);
+    } else if (ret == -EINVAL && out_baseimg && !out_basefmt) {
+        error_report("Could not change the backing file to '%s': backing "
+                     "format must be specified", out_baseimg);
     } else if (ret < 0) {
         error_report("Could not change the backing file to '%s': %s",
             out_baseimg, strerror(-ret));

diff --git a/tests/qemu-iotests/114.out b/tests/qemu-iotests/114.out
index 6d638da266e495e8bed2fbcf919e938edd8cd44b..f51dd9d20a1038c54d7d6e073b5ef72489072cbd 100644 (file)
--- a/tests/qemu-iotests/114.out
+++ b/tests/qemu-iotests/114.out
@@ -14,7 +14,7 @@ qemu-io: can't open device TEST_DIR/t.qcow2: Could not open backing file: Unknow
 no file open, try 'help open'
 read 4096/4096 bytes at offset 0
 4 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
-qemu-img: Could not change the backing file to 'TEST_DIR/t.qcow2.base': Invalid argument
+qemu-img: Could not change the backing file to 'TEST_DIR/t.qcow2.base': backing format must be specified
 read 4096/4096 bytes at offset 0
 4 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 *** done