[Qemu-devel] [PATCH 3/3] Add nocreate option to snapshot_blkdev

[Federico Simoncelli <fsimonce@redhat.com>]

Signed-off-by: Federico Simoncelli <fsimonce@redhat.com>
---
 blockdev.c       |   14 ++++++++------
 hmp-commands.hx  |   16 ++++++++++------
 hmp.c            |    4 +++-
 qapi-schema.json |    8 +++++++-
 qmp-commands.hx  |    2 +-
 5 files changed, 29 insertions(+), 15 deletions(-)

diff --git a/blockdev.c b/blockdev.c
index 7a6613a..2c3e10a 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -647,7 +647,7 @@ void do_commit(Monitor *mon, const QDict *qdict)
 
 void qmp_blockdev_snapshot_sync(const char *device, const char *snapshot_file,
                                 bool has_format, const char *format,
-                                Error **errp)
+                                bool has_nocreate, bool nocreate, Error **errp)
 {
     BlockDriverState *bs;
     BlockDriver *drv, *old_drv, *proto_drv;
@@ -686,11 +686,13 @@ void qmp_blockdev_snapshot_sync(const char *device, const char *snapshot_file,
         return;
     }
 
-    ret = bdrv_img_create(snapshot_file, format, bs->filename,
-                          bs->drv->format_name, NULL, -1, flags);
-    if (ret) {
-        error_set(errp, QERR_UNDEFINED_ERROR);
-        return;
+    if (!(has_nocreate && nocreate)) {
+        ret = bdrv_img_create(snapshot_file, format, bs->filename,
+                              bs->drv->format_name, NULL, -1, flags);
+        if (ret) {
+            error_set(errp, QERR_UNDEFINED_ERROR);
+            return;
+        }
     }
 
     bdrv_drain_all();
diff --git a/hmp-commands.hx b/hmp-commands.hx
index 573b823..ff49412 100644
--- a/hmp-commands.hx
+++ b/hmp-commands.hx
@@ -868,14 +868,18 @@ ETEXI
 
     {
         .name       = "snapshot_blkdev",
-        .args_type  = "device:B,snapshot-file:s?,format:s?",
-        .params     = "device [new-image-file] [format]",
+        .args_type  = "nocreate:-n,device:B,snapshot-file:s?,format:s?",
+        .params     = "[-n] device [new-image-file] [format]",
         .help       = "initiates a live snapshot\n\t\t\t"
                       "of device. If a new image file is specified, the\n\t\t\t"
-                      "new image file will become the new root image.\n\t\t\t"
-                      "If format is specified, the snapshot file will\n\t\t\t"
-                      "be created in that format. Otherwise the\n\t\t\t"
-                      "snapshot will be internal! (currently unsupported)",
+                      "new image file will be created (unless -n is\n\t\t\t"
+                      "specified) and will become the new root image.\n\t\t\t"
+                      "The -n (nocreate) option is potentially dangerous\n\t\t\t"
+                      "if the image wasn't prepared in the correct way\n\t\t\t"
+                      "by an external manager. If format is specified,\n\t\t\t"
+                      "the snapshot file will be created in that format.\n\t\t\t"
+                      "Otherwise the snapshot will be internal!\n\t\t\t"
+                      "(currently unsupported)",
         .mhandler.cmd = hmp_snapshot_blkdev,
     },
 
diff --git a/hmp.c b/hmp.c
index 8ff8c94..44868c7 100644
--- a/hmp.c
+++ b/hmp.c
@@ -684,6 +684,7 @@ void hmp_block_resize(Monitor *mon, const QDict *qdict)
 
 void hmp_snapshot_blkdev(Monitor *mon, const QDict *qdict)
 {
+    int nocreate = qdict_get_try_bool(qdict, "nocreate", 0);
     const char *device = qdict_get_str(qdict, "device");
     const char *filename = qdict_get_try_str(qdict, "snapshot-file");
     const char *format = qdict_get_try_str(qdict, "format");
@@ -697,7 +698,8 @@ void hmp_snapshot_blkdev(Monitor *mon, const QDict *qdict)
         return;
     }
 
-    qmp_blockdev_snapshot_sync(device, filename, !!format, format, &errp);
+    qmp_blockdev_snapshot_sync(device, filename,
+                               !!format, format, true, nocreate, &errp);
     hmp_handle_error(mon, &errp);
 }
 
diff --git a/qapi-schema.json b/qapi-schema.json
index d02ee86..ac652c2 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -1116,9 +1116,14 @@
 # @snapshot-file: the target of the new image. If the file exists, or if it
 #                 is a device, the snapshot will be created in the existing
 #                 file/device. If does not exist, a new file will be created.
+#                 This behavior can be overridden using the nocreate option.
 #
 # @format: #optional the format of the snapshot image, default is 'qcow2'.
 #
+# @nocreate: #optional use the target image avoiding the creation. This is
+#            a potentially dangerous option if the image wasn't prepared
+#            in the correct way by an external manager.
+#
 # Returns: nothing on success
 #          If @device is not a valid block device, DeviceNotFound
 #          If @snapshot-file can't be opened, OpenFileFailed
@@ -1133,7 +1138,8 @@
 # Since 0.14.0
 ##
 { 'command': 'blockdev-snapshot-sync',
-  'data': { 'device': 'str', 'snapshot-file': 'str', '*format': 'str' } }
+  'data': { 'device': 'str', 'snapshot-file': 'str', '*format': 'str',
+            '*nocreate': 'bool' } }
 
 ##
 # @human-monitor-command:
diff --git a/qmp-commands.hx b/qmp-commands.hx
index b5e2ab8..e717826 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -668,7 +668,7 @@ EQMP
 
     {
         .name       = "blockdev-snapshot-sync",
-        .args_type  = "device:B,snapshot-file:s,format:s?",
+        .args_type  = "nocreate:-n,device:B,snapshot-file:s,format:s?",
         .mhandler.cmd_new = qmp_marshal_input_blockdev_snapshot_sync,
     },
 
-- 
1.7.1