[Qemu-devel] [PATCH v3 8/8] add drive-mirror command and HMP equivalent

[Paolo Bonzini]

Since QMP transactions are supposed to take (pseudo) QMP commands,
add a standalone drive-mirror command.

The corresponding HMP command does not provide atomic snapshot+mirror,
but it can still be used together with image streaming.

Signed-off-by: Paolo Bonzini <address@hidden>
---
 blockdev.c       |   24 ++++++++++++++++++++++++
 hmp-commands.hx  |   22 ++++++++++++++++++++++
 hmp.c            |   28 ++++++++++++++++++++++++++++
 hmp.h            |    1 +
 qapi-schema.json |   26 ++++++++++++++++++++++++++
 qmp-commands.hx  |   33 +++++++++++++++++++++++++++++++++
 6 files changed, 134 insertions(+), 0 deletions(-)

diff --git a/blockdev.c b/blockdev.c
index df086d1..60fdc7b 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -671,6 +671,30 @@ void qmp_blockdev_snapshot_sync(const char *device, const 
char *snapshot_file,
     qmp_transaction(&list, errp);
 }
 
+void qmp_drive_mirror(const char *device, const char *target,
+                      bool has_format, const char *format,
+                      bool has_mode, enum NewImageMode mode, Error **errp)
+{
+    BlockdevMirror mirror = {
+        .device = (char *) device,
+        .target = (char *) target,
+        .has_format = has_format,
+        .format = (char *) format,
+        .has_mode = has_mode,
+        .mode = mode,
+    };
+    BlockdevAction action = {
+        .kind = BLOCKDEV_ACTION_KIND_DRIVE_MIRROR,
+        .drive_mirror = &mirror,
+    };
+    BlockdevActionList list = {
+        .value = &action,
+        .next = NULL
+    };
+
+    qmp_transaction(&list, errp);
+}
+
 
 /* New and old BlockDriverState structs for group snapshots */
 typedef struct BlkTransactionStates {
diff --git a/hmp-commands.hx b/hmp-commands.hx
index 6980214..9c49c33 100644
--- a/hmp-commands.hx
+++ b/hmp-commands.hx
@@ -903,6 +903,28 @@ Snapshot device, using snapshot file as target if provided
 ETEXI
 
     {
+        .name       = "drive_mirror",
+        .args_type  = "reuse:-n,no-backing:-s,device:B,target:s,format:s?",
+        .params     = "[-n] [-s] device [new-image-file] [format]",
+        .help       = "initiates live storage\n\t\t\t"
+                      "migration for a device. New writes are mirrored to 
the\n\t\t\t"
+                      "specified new image file, and the block_stream\n\t\t\t"
+                      "command can then be started.\n\t\t\t"
+                      "The default format is qcow2.  The -n flag requests 
QEMU\n\t\t\t"
+                      "to reuse the image found in new-image-file, instead 
of\n\t\t\t"
+                      "recreating it from scratch.  The -s flag requests 
QEMU\n\t\t\t"
+                      "to create a root image, that does not have the 
current\n\t\t\t"
+                      "image as the backing file.",
+        .mhandler.cmd = hmp_drive_mirror,
+    },
+STEXI
address@hidden drive_mirror
address@hidden drive_mirror
+Start mirroring a block device's writes to a new destination,
+using the specified target.
+ETEXI
+
+    {
         .name       = "drive_add",
         .args_type  = "pci_addr:s,opts:s",
         .params     = "[[<domain>:]<bus>:]<slot>\n"
diff --git a/hmp.c b/hmp.c
index 290c43d..e706db9 100644
--- a/hmp.c
+++ b/hmp.c
@@ -687,6 +687,34 @@ void hmp_block_resize(Monitor *mon, const QDict *qdict)
     hmp_handle_error(mon, &errp);
 }
 
+void hmp_drive_mirror(Monitor *mon, const QDict *qdict)
+{
+    const char *device = qdict_get_str(qdict, "device");
+    const char *filename = qdict_get_try_str(qdict, "target");
+    const char *format = qdict_get_try_str(qdict, "format");
+    int reuse = qdict_get_try_bool(qdict, "reuse", 0);
+    int no_backing = qdict_get_try_bool(qdict, "no-backing", 0);
+    enum NewImageMode mode;
+    Error *errp = NULL;
+
+    if (!filename) {
+        error_set(&errp, QERR_MISSING_PARAMETER, "target");
+        hmp_handle_error(mon, &errp);
+        return;
+    }
+
+    if (reuse) {
+        mode = NEW_IMAGE_MODE_EXISTING;
+    } else if (no_backing) {
+        mode = NEW_IMAGE_MODE_NO_BACKING_FILE;
+    } else {
+        mode = NEW_IMAGE_MODE_ABSOLUTE_PATHS;
+    }
+
+    qmp_drive_mirror(device, filename, !!format, format, true, mode, &errp);
+    hmp_handle_error(mon, &errp);
+}
+
 void hmp_snapshot_blkdev(Monitor *mon, const QDict *qdict)
 {
     const char *device = qdict_get_str(qdict, "device");
diff --git a/hmp.h b/hmp.h
index 5409464..5352f00 100644
--- a/hmp.h
+++ b/hmp.h
@@ -48,6 +48,7 @@ void hmp_block_passwd(Monitor *mon, const QDict *qdict);
 void hmp_balloon(Monitor *mon, const QDict *qdict);
 void hmp_block_resize(Monitor *mon, const QDict *qdict);
 void hmp_snapshot_blkdev(Monitor *mon, const QDict *qdict);
+void hmp_drive_mirror(Monitor *mon, const QDict *qdict);
 void hmp_migrate_cancel(Monitor *mon, const QDict *qdict);
 void hmp_migrate_set_downtime(Monitor *mon, const QDict *qdict);
 void hmp_migrate_set_speed(Monitor *mon, const QDict *qdict);
diff --git a/qapi-schema.json b/qapi-schema.json
index a61e90c..16e8786 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -1262,6 +1262,33 @@
   'returns': 'str' } 
 
 ##
+# @drive-mirror
+#
+# Start mirroring a block device's writes to a new destination.
+#
+# @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 'qcow2'.
+#
+# @mode: #optional whether and how QEMU should create a new image, default is
+# 'absolute-paths'.
+#
+# Returns: nothing on success
+#          If @device is not a valid block device, DeviceNotFound
+#          If @target can't be opened, OpenFileFailed
+#          If @format is invalid, InvalidBlockFormat
+#
+# Since 1.1
+##
+{ 'command': 'drive-mirror',
+  'data': { 'device': 'str', 'target': 'str', '*format': 'str',
+            '*mode': 'NewImageMode'} }
+
+##
 # @migrate_cancel
 #
 # Cancel the current executing migration process.
diff --git a/qmp-commands.hx b/qmp-commands.hx
index 9dcafd4..b8a93d1 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -785,6 +785,39 @@ Example:
 EQMP
 
     {
+        .name       = "drive-mirror",
+        .args_type  = "device:B,snapshot-file:s,mode:s?,format:s?",
+        .mhandler.cmd_new = qmp_marshal_input_drive_mirror,
+    },
+
+SQMP
+drive-mirror
+------------
+
+Start mirroring a block device's writes to a new destination. target
+specifies the target of the new image. If the file exists, or if it is
+a device, it will be used as the new destination for writes. If does not
+exist, a new file will be created. format specifies the format of the
+mirror image, default is qcow2.
+
+Arguments:
+
+- "device": device name to operate on (json-string)
+- "target": name of new image file (json-string)
+- "format": format of new image (json-string, optional)
+- "mode": how an image file should be created into the target
+  file/device (NewImageMode, optional, default 'absolute-paths')
+
+Example:
+
+-> { "execute": "drive-mirror", "arguments": { "device": "ide-hd0",
+                                               "target": 
"/some/place/my-image",
+                                               "format": "qcow2" } }
+<- { "return": {} }
+
+EQMP
+
+    {
         .name       = "balloon",
         .args_type  = "value:M",
         .mhandler.cmd_new = qmp_marshal_input_balloon,
-- 
1.7.7.6