[Qemu-devel] [RFC v2 PATCH 6/6] QAPI: add command for live block commit, 'block-commit'

[Jeff Cody]

The command for live block commit is added, which has the following
arguments:

device: the block device to perform the commit on (mandatory)
base:   the base image to commit into; optional (if not specified,
        it is the underlying original image)
top:    the top image of the commit - all data from inside top down
        to base will be committed into base. optional (if not specified,
        it is the active image) - see note below
speed:  maximum speed, in bytes/sec

note: eventually this will support merging down the active layer,
      but that code is not yet complete.  If the active layer is passed
      in currently as top, or top is left to the default, then the error
      QERR_TOP_NOT_FOUND will be returned.

The is done as a block job, so upon completion a BLOCK_JOB_COMPLETED will
be emitted.

Signed-off-by: Jeff Cody <address@hidden>
---
 blockdev.c       | 83 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 qapi-schema.json | 30 ++++++++++++++++++++
 qmp-commands.hx  |  6 ++++
 3 files changed, 119 insertions(+)

diff --git a/blockdev.c b/blockdev.c
index 68d65fb..e0d6ca0 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -827,6 +827,89 @@ exit:
     return;
 }
 
+void qmp_block_commit(const char *device,
+                      bool has_base, const char *base,
+                      bool has_top, const char *top,
+                      bool has_speed, int64_t speed,
+                      Error **errp)
+{
+    BlockDriverState *bs;
+    BlockDriverState *base_bs, *top_bs, *child_bs;
+    Error *local_err = NULL;
+    int orig_base_flags, orig_top_flags;
+    BlockReopenQueue *reopen_queue = NULL;
+    /* This will be part of the QMP command, if/when the
+     * BlockdevOnError change for blkmirror makes it in
+     */
+    BlockErrorAction on_error = BLOCK_ERR_REPORT;
+
+    /* drain all i/o before commits */
+    bdrv_drain_all();
+
+    bs = bdrv_find(device);
+    if (!bs) {
+        error_set(errp, QERR_DEVICE_NOT_FOUND, device);
+        return;
+    }
+    if (base && has_base) {
+        base_bs = bdrv_find_backing_image(bs, base);
+    } else {
+        base_bs = bdrv_find_base(bs);
+    }
+
+    if (base_bs == NULL) {
+        error_set(errp, QERR_BASE_NOT_FOUND, "NULL");
+        return;
+    }
+
+    if (top && has_top) {
+        /* if we want to allow the active layer,
+         * use 'bdrv_find_image()' here */
+        top_bs = bdrv_find_backing_image(bs, top);
+        if (top_bs == NULL) {
+            error_set(errp, QERR_TOP_NOT_FOUND, top);
+            return;
+        }
+    } else {
+        /* we will eventually default to the top layer,i.e. top_bs = bs */
+        error_set(errp, QERR_TOP_NOT_FOUND, top);
+        return;
+    }
+
+    child_bs = bdrv_find_child(bs, top_bs);
+
+    orig_base_flags = bdrv_get_flags(base_bs);  /* what we are writing into   
*/
+    orig_top_flags = bdrv_get_flags(child_bs);  /* to change the backing file 
*/
+
+    /* convert base_bs to r/w, if necessary */
+    if (!(orig_base_flags & BDRV_O_RDWR)) {
+        reopen_queue = bdrv_reopen_queue(reopen_queue, base_bs,
+                                         orig_base_flags | BDRV_O_RDWR);
+    }
+    if (!(orig_top_flags & BDRV_O_RDWR)) {
+        reopen_queue = bdrv_reopen_queue(reopen_queue, base_bs,
+                                         orig_base_flags | BDRV_O_RDWR);
+    }
+    if (reopen_queue) {
+        bdrv_reopen_multiple(reopen_queue, &local_err);
+        if (local_err != NULL) {
+            error_propagate(errp, local_err);
+            return;
+        }
+    }
+
+    commit_start(bs, base_bs, top_bs, speed, on_error,
+                 block_job_cb, bs, orig_base_flags, orig_top_flags,
+                 &local_err);
+    if (local_err != NULL) {
+        error_propagate(errp, local_err);
+        return;
+    }
+    /* Grab a reference so hotplug does not delete the BlockDriverState from
+     * underneath us.
+     */
+    drive_get_ref(drive_get_by_blockdev(bs));
+}
 
 static void eject_device(BlockDriverState *bs, int force, Error **errp)
 {
diff --git a/qapi-schema.json b/qapi-schema.json
index bd8ad74..45feda6 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -1401,6 +1401,36 @@
   'returns': 'str' }
 
 ##
+# @block-commit
+#
+# Live commit of data from child image nodes into parent nodes - i.e.,
+# writes data between 'top' and 'base' into 'base'.
+#
+# @device:  the name of the device
+#
+# @base:   #optional The parent image of the device to write data into.
+#                    If not specified, this is the original parent image.
+#
+# @top:    #optional The child image, above which data will not be committed
+#                    down.  If not specified, this is the active layer.
+#
+# @speed:  #optional the maximum speed, in bytes per second
+#
+# Returns: Nothing on success
+#          If commit or stream is already active on this device, DeviceInUse
+#          If @device does not exist, DeviceNotFound
+#          If image commit is not supported by this device, NotSupported
+#          If @base does not exist, BaseNotFound
+#          If @top does not exist, TopNotFound
+#          If @speed is invalid, InvalidParameter
+#
+# Since: 1.2
+#
+##
+{ 'command': 'block-commit',
+  'data': { 'device': 'str', '*base': 'str', '*top': 'str',
+            '*speed': 'int' } }
+
 # @migrate_cancel
 #
 # Cancel the current executing migration process.
diff --git a/qmp-commands.hx b/qmp-commands.hx
index 3745a21..9292877 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -767,6 +767,12 @@ EQMP
     },
 
     {
+        .name       = "block-commit",
+        .args_type  = "device:B,base:s?,top:s?,speed:o?",
+        .mhandler.cmd_new = qmp_marshal_input_block_commit,
+    },
+
+    {
         .name       = "block-job-set-speed",
         .args_type  = "device:B,speed:o",
         .mhandler.cmd_new = qmp_marshal_input_block_job_set_speed,
-- 
1.7.11.2