[Qemu-devel] [PATCH v6 2/3] block: Add drive-mirror-replace command

[Benoît Canet]

When a quorum file is totally destroyed (broken NAS or SAN) the user can start a
drive-mirror job on the quorum block backend and then replace the broken
quorum file with drive-mirror-replace given it has a node-name.

Signed-off-by: Benoit Canet <address@hidden>
---
 block.c                   |   8 ++--
 block/mirror.c            | 118 ++++++++++++++++++++++++++++++++++++++++++++--
 blockdev.c                |  27 +++++++++++
 include/block/block.h     |   3 ++
 include/block/block_int.h |  15 ++++++
 qapi/block-core.json      |  33 +++++++++++++
 qmp-commands.hx           |   5 ++
 trace-events              |   1 +
 8 files changed, 204 insertions(+), 6 deletions(-)

diff --git a/block.c b/block.c
index 17f763d..ab966f3 100644
--- a/block.c
+++ b/block.c
@@ -844,10 +844,12 @@ static int bdrv_open_flags(BlockDriverState *bs, int 
flags)
     return open_flags;
 }
 
-static void bdrv_assign_node_name(BlockDriverState *bs,
-                                  const char *node_name,
-                                  Error **errp)
+void bdrv_assign_node_name(BlockDriverState *bs,
+                           const char *node_name,
+                           Error **errp)
 {
+    assert(bs->node_name[0] == '\0');
+
     if (!node_name) {
         return;
     }
diff --git a/block/mirror.c b/block/mirror.c
index 94c8661..2d4c0ed 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -49,6 +49,15 @@ typedef struct MirrorBlockJob {
     unsigned long *in_flight_bitmap;
     int in_flight;
     int ret;
+    /* these four fields are used by drive-mirror-replace */
+    /* The code must replace a target with the new mirror */
+    bool must_replace;
+    /* The block BDS to replace */
+    BlockDriverState *to_replace;
+    /* the node-name of the new mirror BDS */
+    char *new_node_name;
+    /* Used to block operations on the drive-mirror-replace target. */
+    Error *replace_blocker;
 } MirrorBlockJob;
 
 typedef struct MirrorOp {
@@ -313,6 +322,7 @@ static void coroutine_fn mirror_run(void *opaque)
     MirrorBlockJob *s = opaque;
     BlockDriverState *bs = s->common.bs;
     int64_t sector_num, end, sectors_per_chunk, length;
+    BlockDriverState *to_replace;
     uint64_t last_pause_ns;
     BlockDriverInfo bdi;
     char backing_filename[1024];
@@ -489,11 +499,17 @@ immediate_exit:
     g_free(s->in_flight_bitmap);
     bdrv_release_dirty_bitmap(bs, s->dirty_bitmap);
     bdrv_iostatus_disable(s->target);
+    /* Here we handle the drive-mirror-replace QMP command */
+    if (s->must_replace) {
+        to_replace = s->to_replace;
+    } else {
+        to_replace = s->common.bs;
+    }
     if (s->should_complete && ret == 0) {
-        if (bdrv_get_flags(s->target) != bdrv_get_flags(s->common.bs)) {
-            bdrv_reopen(s->target, bdrv_get_flags(s->common.bs), NULL);
+        if (bdrv_get_flags(s->target) != bdrv_get_flags(to_replace)) {
+            bdrv_reopen(s->target, bdrv_get_flags(to_replace), NULL);
         }
-        bdrv_swap(s->target, s->common.bs);
+        bdrv_swap(s->target, to_replace);
         if (s->common.driver->job_type == BLOCK_JOB_TYPE_COMMIT) {
             /* drop the bs loop chain formed by the swap: break the loop then
              * trigger the unref from the top one */
@@ -502,6 +518,11 @@ immediate_exit:
             bdrv_unref(p);
         }
     }
+    if (s->must_replace) {
+        bdrv_op_unblock_all(s->to_replace, s->replace_blocker);
+        error_free(s->replace_blocker);
+        bdrv_unref(s->to_replace);
+    }
     bdrv_unref(s->target);
     block_job_completed(&s->common, ret);
 }
@@ -524,6 +545,90 @@ static void mirror_iostatus_reset(BlockJob *job)
     bdrv_iostatus_reset(s->target);
 }
 
+bool mirror_set_replace_target(BlockJob *job, const char *reference,
+                               bool has_new_node_name,
+                               const char *new_node_name, Error **errp)
+{
+    MirrorBlockJob *s = container_of(job, MirrorBlockJob, common);
+    BlockDriverState *to_replace;
+
+    /* We don't want to give too much power to the user as this could result in
+     * BlockDriverState loops if used with something other than sync=full.
+     */
+    if (s->is_none_mode || s->base) {
+        error_setg(errp, "Can only be used on a mirror done with sync=full");
+        return false;
+    }
+
+    /* check that the target reference is not an empty string */
+    if (!reference[0]) {
+        error_setg(errp, "target-reference is an empty string");
+        return false;
+    }
+
+    /* Get the block driver state to be replaced */
+    to_replace = bdrv_lookup_bs(reference, reference, errp);
+    if (!to_replace) {
+        return false;
+    }
+
+    /* If the BDS to be replaced is a regular node we need a new node name */
+    if (to_replace->node_name[0] && !has_new_node_name) {
+        error_setg(errp, "A new-node-name must be provided");
+        return false;
+    }
+
+    /* Can only replace something else than the source of the mirror */
+    if (to_replace == job->bs) {
+        error_setg(errp, "Cannot replace the mirror source");
+        return false;
+    }
+
+    /* is this bs replace operation blocked */
+    if (bdrv_op_is_blocked(to_replace, BLOCK_OP_TYPE_REPLACE, errp)) {
+        return false;
+    }
+
+    /* save useful infos for later */
+    s->to_replace = to_replace;
+    /* don't make any assumption on new_node_name state if !has_new_node_name 
*/
+    s->new_node_name = has_new_node_name ? g_strdup(new_node_name) : NULL;
+
+    return true;
+}
+
+static void mirror_activate_replace_target(BlockJob *job, Error **errp)
+{
+    MirrorBlockJob *s = container_of(job, MirrorBlockJob, common);
+    Error *local_err = NULL;
+
+    /* Set the new node name if the BDS to replace is a regular node
+     * of the graph.
+     */
+    if (s->to_replace->node_name[0]) {
+        assert(s->new_node_name);
+        bdrv_assign_node_name(s->target, s->new_node_name, &local_err);
+    }
+
+    g_free(s->new_node_name);
+
+    if (local_err) {
+        s->to_replace = NULL;
+        error_propagate(errp, local_err);
+        return;
+    }
+
+    /* block all operations on the target bs */
+    error_setg(&s->replace_blocker,
+               "block device is in use by drive-mirror-replace");
+    bdrv_op_block_all(s->to_replace, s->replace_blocker);
+
+    bdrv_ref(s->to_replace);
+
+    /* activate the replacement operation */
+    s->must_replace = true;
+}
+
 static void mirror_complete(BlockJob *job, Error **errp)
 {
     MirrorBlockJob *s = container_of(job, MirrorBlockJob, common);
@@ -540,6 +645,13 @@ static void mirror_complete(BlockJob *job, Error **errp)
         return;
     }
 
+    /* drive-mirror-replace is being called on this job so activate the
+     * replacement target
+     */
+    if (s->to_replace) {
+        mirror_activate_replace_target(job, errp);
+    }
+
     s->should_complete = true;
     block_job_resume(job);
 }
diff --git a/blockdev.c b/blockdev.c
index 4cbcc56..1f10438 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -2326,6 +2326,33 @@ void qmp_block_job_complete(const char *device, Error 
**errp)
     block_job_complete(job, errp);
 }
 
+void qmp_drive_mirror_replace(const char *device, const char *target_reference,
+                              bool has_new_node_name,
+                              const char *new_node_name,
+                              Error **errp)
+{
+    BlockJob *job = find_block_job(device);
+
+    if (!job) {
+        error_set(errp, QERR_BLOCK_JOB_NOT_ACTIVE, device);
+        return;
+    }
+
+    if (!job->driver || job->driver->job_type != BLOCK_JOB_TYPE_MIRROR) {
+        error_setg(errp, "Can only be used on a drive-mirror block job");
+        return;
+    }
+
+    if (!mirror_set_replace_target(job, target_reference, has_new_node_name,
+                                   new_node_name, errp)) {
+        return;
+    }
+
+    trace_qmp_drive_mirror_replace(job, target_reference,
+                                   has_new_node_name ? new_node_name : "");
+    block_job_complete(job, errp);
+}
+
 void qmp_blockdev_add(BlockdevOptions *options, Error **errp)
 {
     QmpOutputVisitor *ov = qmp_output_visitor_new();
diff --git a/include/block/block.h b/include/block/block.h
index 7d86e29..444b352 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -179,6 +179,7 @@ typedef enum BlockOpType {
     BLOCK_OP_TYPE_MIRROR,
     BLOCK_OP_TYPE_RESIZE,
     BLOCK_OP_TYPE_STREAM,
+    BLOCK_OP_TYPE_REPLACE,
     BLOCK_OP_TYPE_MAX,
 } BlockOpType;
 
@@ -217,6 +218,8 @@ int bdrv_open_image(BlockDriverState **pbs, const char 
*filename,
                     QDict *options, const char *bdref_key, int flags,
                     bool allow_none, Error **errp);
 void bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd);
+void bdrv_assign_node_name(BlockDriverState *bs, const char *node_name,
+                           Error **errp);
 int bdrv_open_backing_file(BlockDriverState *bs, QDict *options, Error **errp);
 void bdrv_append_temp_snapshot(BlockDriverState *bs, int flags, Error **errp);
 int bdrv_open(BlockDriverState **pbs, const char *filename,
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 8d58334..b8e1375 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -515,6 +515,21 @@ void mirror_start(BlockDriverState *bs, BlockDriverState 
*target,
                   void *opaque, Error **errp);
 
 /*
+ * mirror_set_replace_target:
+ * @job: An active mirroring block job started with sync=full.
+ * @reference: id or node-name of the BDS to replace when the mirror is done.
+ * @has_new_node_name: Set to true if new_node_name if provided
+ * @new_node_name: The optional new node name of the new mirror.
+ * @errp: Error object.
+ *
+ * Prepare a mirroring operation to replace a BDS pointed to by reference with
+ * the new mirror.
+ */
+bool mirror_set_replace_target(BlockJob *job, const char *reference,
+                               bool has_new_node_name,
+                               const char *new_node_name, Error **errp);
+
+/*
  * backup_start:
  * @bs: Block device to operate on.
  * @target: Block device to write to.
diff --git a/qapi/block-core.json b/qapi/block-core.json
index eec881b..7efb291 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -1417,3 +1417,36 @@
 ##
 { 'command': 'blockdev-add', 'data': { 'options': 'BlockdevOptions' } }
 
+##
+# @drive-mirror-replace:
+#
+# Manually trigger completion of an active background drive-mirror operation
+# and replace the target reference with the new mirror.
+# This switches the device to write to the target path only.
+# The ability to complete is signaled with a BLOCK_JOB_READY event.
+#
+# This command completes an active drive-mirror background operation
+# synchronously and replaces the target reference with the mirror.
+# The ordering of this command's return with the BLOCK_JOB_COMPLETED event
+# is not defined.  Note that if an I/O error occurs during the processing of
+# this command: 1) the command itself will fail; 2) the error will be processed
+# according to the rerror/werror arguments that were specified when starting
+# the operation.
+#
+# A cancelled or paused drive-mirror job cannot be completed.
+#
+# @device:           the device name
+# @target-reference: the id or node name of the block driver state to replace
+# @new-node-name:    #optional set the node-name of the new block driver state
+#                    needed if the target reference points to a regular node of
+#                    the graph
+#
+# Returns: Nothing on success
+#          If no background operation is active on this device, DeviceNotActive
+#
+# Since: 2.1
+##
+{ 'command': 'drive-mirror-replace',
+  'data': { 'device': 'str', 'target-reference': 'str',
+            '*new-node-name': 'str' } }
+
diff --git a/qmp-commands.hx b/qmp-commands.hx
index d8aa4ed..3421d90 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -1106,6 +1106,11 @@ EQMP
         .mhandler.cmd_new = qmp_marshal_input_block_job_complete,
     },
     {
+        .name       = "drive-mirror-replace",
+        .args_type  = "device:B,target-reference:s,new-node-name:s?",
+        .mhandler.cmd_new = qmp_marshal_input_drive_mirror_replace,
+    },
+    {
         .name       = "transaction",
         .args_type  = "actions:q",
         .mhandler.cmd_new = qmp_marshal_input_transaction,
diff --git a/trace-events b/trace-events
index ffe6e62..ddfa4a2 100644
--- a/trace-events
+++ b/trace-events
@@ -103,6 +103,7 @@ qmp_block_job_cancel(void *job) "job %p"
 qmp_block_job_pause(void *job) "job %p"
 qmp_block_job_resume(void *job) "job %p"
 qmp_block_job_complete(void *job) "job %p"
+qmp_drive_mirror_replace(void *job, const char *target_reference, const char 
*new_node_name) "job %p target_reference %s new_node_name %s"
 block_job_cb(void *bs, void *job, int ret) "bs %p job %p ret %d"
 qmp_block_stream(void *bs, void *job) "bs %p job %p"
 
-- 
1.9.1