[Qemu-block] [PATCH 2/3] block: Add 'blockdev-del' QMP command

[Alberto Garcia]

This is the companion to 'blockdev-add'. It allows deleting a
BlockBackend with its associated BlockDriverState tree, or a
BlockDriverState that is not attached to any backend.

In either case, the command fails if the reference count is greater
than 1 or the BlockDriverState has any parents.

Signed-off-by: Alberto Garcia <address@hidden>
---
 blockdev.c           | 42 ++++++++++++++++++++++++++++++++++++++++++
 qapi/block-core.json | 21 +++++++++++++++++++++
 qmp-commands.hx      | 36 ++++++++++++++++++++++++++++++++++++
 3 files changed, 99 insertions(+)

diff --git a/blockdev.c b/blockdev.c
index 2360c1f..c448a0b 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -3402,6 +3402,48 @@ fail:
     qmp_output_visitor_cleanup(ov);
 }
 
+void qmp_blockdev_del(const char *device, Error **errp)
+{
+    AioContext *aio_context;
+    BlockBackend *blk;
+    BlockDriverState *bs;
+
+    blk = blk_by_name(device);
+    if (blk) {
+        bs = blk_bs(blk);
+        aio_context = blk_get_aio_context(blk);
+    } else {
+        bs = bdrv_find_node(device);
+        if (!bs) {
+            error_setg(errp, "Cannot find block device %s", device);
+            return;
+        }
+        blk = bs->blk;
+        aio_context = bdrv_get_aio_context(bs);
+    }
+
+    aio_context_acquire(aio_context);
+
+    if (bs && bdrv_op_is_blocked(bs, BLOCK_OP_TYPE_DRIVE_DEL, errp)) {
+        goto out;
+    }
+
+    if (blk_get_refcnt(blk) > 1 ||
+        (bs && (bs->refcnt > 1 || !QLIST_EMPTY(&bs->parents)))) {
+        error_setg(errp, "Block device %s is being used", device);
+        goto out;
+    }
+
+    if (blk) {
+        blk_unref(blk);
+    } else {
+        bdrv_unref(bs);
+    }
+
+out:
+    aio_context_release(aio_context);
+}
+
 BlockJobInfoList *qmp_query_block_jobs(Error **errp)
 {
     BlockJobInfoList *head = NULL, **p_next = &head;
diff --git a/qapi/block-core.json b/qapi/block-core.json
index 5f12af7..20897eb 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -1877,6 +1877,27 @@
 { 'command': 'blockdev-add', 'data': { 'options': 'BlockdevOptions' } }
 
 ##
+# @blockdev-del:
+#
+# Deletes a block device. The selected device can be either a block
+# backend or a graph node.
+#
+# In the former case the backend will be destroyed, along with its
+# inserted medium if there's any.
+#
+# In the latter case the node will be destroyed, along with the
+# backend it is attached to if there's any.
+#
+# The command will fail if the selected block device is still being
+# used.
+#
+# @device: Name of the block backend or the graph node to be deleted.
+#
+# Since: 2.5
+##
+{ 'command': 'blockdev-del', 'data': { 'device': 'str' } }
+
+##
 # @blockdev-open-tray:
 #
 # Opens a block device's tray. If there is a block driver state tree inserted 
as
diff --git a/qmp-commands.hx b/qmp-commands.hx
index 4f03d11..b8b133e 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -3921,6 +3921,42 @@ Example (2):
 EQMP
 
     {
+        .name       = "blockdev-del",
+        .args_type  = "device:s",
+        .mhandler.cmd_new = qmp_marshal_blockdev_del,
+    },
+
+SQMP
+blockdev-del
+------------
+Since 2.5
+
+Deletes a block device. The selected device can be either a block
+backend or a graph node.
+
+In the former case the backend will be destroyed, along with its
+inserted medium if there's any.
+
+In the latter case the node will be destroyed, along with the
+backend it is attached to if there's any.
+
+The command will fail if the selected block device is still being
+used.
+
+Arguments:
+
+- "device": Identifier of the block device or graph node name (json-string)
+
+Example:
+
+-> { "execute": "blockdev-del",
+                "arguments": { "device": "virtio0" }
+   }
+<- { "return": {} }
+
+EQMP
+
+    {
         .name       = "blockdev-open-tray",
         .args_type  = "device:s,force:b?",
         .mhandler.cmd_new = qmp_marshal_blockdev_open_tray,
-- 
2.6.1