block: add block_resize monitor command

Add a monitor command that allows resizing of block devices while
qemu is running.  It uses the existing bdrv_truncate method already
used by qemu-img to do it's work.  Compared to qemu-img the size
parsing is very simplicistic, but I think having a properly numering
object is more useful for non-humand monitor users than having
the units and relative resize parsing.

For SCSI devices the new size can be updated in Linux guests by
doing the following shell command:

	echo > /sys/class/scsi_device/0:0:0:0/device/rescan

For ATA devices I don't know of a way to update the block device
size in Linux system, and for virtio-blk the next two patches
will provide an automatic update of the size when this command
is issued on the host.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 28 insertions, 0 deletions

diff --git a/qmp-commands.hx b/qmp-commands.hx
index 56c4d8bc47..9f79f5fdf2 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -601,6 +601,34 @@ Example:
 -> { "execute": "netdev_del", "arguments": { "id": "netdev1" } }
 <- { "return": {} }
 
+
+EQMP
+
+    {
+        .name       = "block_resize",
+        .args_type  = "device:B,size:o",
+        .params     = "device size",
+        .help       = "resize a block image",
+        .user_print = monitor_user_noop,
+        .mhandler.cmd_new = do_block_resize,
+    },
+
+SQMP
+block_resize
+------------
+
+Resize a block image while a guest is running.
+
+Arguments:
+
+- "device": the device's ID, must be unique (json-string)
+- "size": new size
+
+Example:
+
+-> { "execute": "block_resize", "arguments": { "device": "scratch", "size": 1073741824 } }
+<- { "return": {} }
+
 EQMP
 
     {