[Qemu-devel] [PATCH v6 09/12] blockdev: add DriveBackup transaction

[Stefan Hajnoczi <stefanha@redhat.com>]

This patch adds a transactional version of the drive-backup QMP command.
It allows atomic snapshots of multiple drives along with automatic
cleanup if there is a failure to start one of the backup jobs.

Note that QMP events are emitted for block job completion/cancellation
and the block job will be listed by query-block-jobs.

@device: the name of the device whose writes should be mirrored.

@target: the target of the new image. If the file exists, or if it
         is a device, the existing file/device will be used as the new
         destination.  If it does not exist, a new file will be created.

@format: #optional the format of the new destination, default is to
         probe if @mode is 'existing', else the format of the source

@mode: #optional whether and how QEMU should create a new image, default is
       'absolute-paths'.

@speed: #optional the maximum speed, in bytes per second

@on-source-error: #optional the action to take on an error on the source,
                  default 'report'.  'stop' and 'enospc' can only be used
                  if the block device supports io-status (see BlockInfo).

@on-target-error: #optional the action to take on an error on the target,
                  default 'report' (no limitations, since this applies to
                  a different block device than @device).

Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 blockdev.c       | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
 qapi-schema.json | 40 +++++++++++++++++++++++++++++++++++++++-
 2 files changed, 88 insertions(+), 1 deletion(-)

diff --git a/blockdev.c b/blockdev.c
index 8dc6f2e..8caeac4 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -919,6 +919,50 @@ static void external_snapshot_abort(BlkTransactionState *common)
     }
 }
 
+typedef struct DriveBackupState {
+    BlkTransactionState common;
+    BlockDriverState *bs;
+    BlockJob *job;
+} DriveBackupState;
+
+static void drive_backup_prepare(BlkTransactionState *common, Error **errp)
+{
+    DriveBackupState *state = DO_UPCAST(DriveBackupState, common, common);
+    DriveBackup *backup;
+    Error *local_err = NULL;
+
+    assert(common->action->kind == TRANSACTION_ACTION_KIND_DRIVE_BACKUP);
+    backup = common->action->drive_backup;
+
+    qmp_drive_backup(backup->device, backup->target,
+                     backup->has_format, backup->format,
+                     backup->has_mode, backup->mode,
+                     backup->has_speed, backup->speed,
+                     backup->has_on_source_error, backup->on_source_error,
+                     backup->has_on_target_error, backup->on_target_error,
+                     &local_err);
+    if (error_is_set(&local_err)) {
+        error_propagate(errp, local_err);
+        state->bs = NULL;
+        state->job = NULL;
+        return;
+    }
+
+    state->bs = bdrv_find(backup->device);
+    state->job = state->bs->job;
+}
+
+static void drive_backup_abort(BlkTransactionState *common)
+{
+    DriveBackupState *state = DO_UPCAST(DriveBackupState, common, common);
+    BlockDriverState *bs = state->bs;
+
+    /* Only cancel if it's the job we started */
+    if (bs && bs->job && bs->job == state->job) {
+        block_job_cancel_sync(bs->job);
+    }
+}
+
 static const BdrvActionOps actions[] = {
     [TRANSACTION_ACTION_KIND_BLOCKDEV_SNAPSHOT_SYNC] = {
         .instance_size = sizeof(ExternalSnapshotState),
@@ -926,6 +970,11 @@ static const BdrvActionOps actions[] = {
         .commit   = external_snapshot_commit,
         .abort = external_snapshot_abort,
     },
+    [TRANSACTION_ACTION_KIND_DRIVE_BACKUP] = {
+        .instance_size = sizeof(DriveBackupState),
+        .prepare = drive_backup_prepare,
+        .abort = drive_backup_abort,
+    },
 };
 
 /*
diff --git a/qapi-schema.json b/qapi-schema.json
index 8dc9471..f3f6ff6 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -1615,6 +1615,43 @@
             '*mode': 'NewImageMode' } }
 
 ##
+# @DriveBackup
+#
+# @device: the name of the device which should be copied.
+#
+# @target: the target of the new image. If the file exists, or if it
+#          is a device, the existing file/device will be used as the new
+#          destination.  If it does not exist, a new file will be created.
+#
+# @format: #optional the format of the new destination, default is to
+#          probe if @mode is 'existing', else the format of the source
+#
+# @mode: #optional whether and how QEMU should create a new image, default is
+#        'absolute-paths'.
+#
+# @speed: #optional the maximum speed, in bytes per second
+#
+# @on-source-error: #optional the action to take on an error on the source,
+#                   default 'report'.  'stop' and 'enospc' can only be used
+#                   if the block device supports io-status (see BlockInfo).
+#
+# @on-target-error: #optional the action to take on an error on the target,
+#                   default 'report' (no limitations, since this applies to
+#                   a different block device than @device).
+#
+# Note that @on-source-error and @on-target-error only affect background I/O.
+# If an error occurs during a guest write request, the device's rerror/werror
+# actions will be used.
+#
+# Since: 1.6
+##
+{ 'type': 'DriveBackup',
+  'data': { 'device': 'str', 'target': 'str', '*format': 'str',
+            '*mode': 'NewImageMode', '*speed': 'int',
+            '*on-source-error': 'BlockdevOnError',
+            '*on-target-error': 'BlockdevOnError' } }
+
+##
 # @TransactionAction
 #
 # A discriminated record of operations that can be performed with
@@ -1622,7 +1659,8 @@
 ##
 { 'union': 'TransactionAction',
   'data': {
-       'blockdev-snapshot-sync': 'BlockdevSnapshot'
+       'blockdev-snapshot-sync': 'BlockdevSnapshot',
+       'drive-backup': 'DriveBackup'
    } }
 
 ##
-- 
1.8.1.4