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>

blockdev.c

@@ -705,3 +705,33 @@ int do_drive_del(Monitor *mon, const QDict *qdict, QObject **ret_data)
 
     return 0;
 }
+
+/*
+ * XXX: replace the QERR_UNDEFINED_ERROR errors with real values once the
+ * existing QERR_ macro mess is cleaned up.  A good example for better
+ * error reports can be found in the qemu-img resize code.
+ */
+int do_block_resize(Monitor *mon, const QDict *qdict, QObject **ret_data)
+{
+    const char *device = qdict_get_str(qdict, "device");
+    int64_t size = qdict_get_int(qdict, "size");
+    BlockDriverState *bs;
+
+    bs = bdrv_find(device);
+    if (!bs) {
+        qerror_report(QERR_DEVICE_NOT_FOUND, device);
+        return -1;
+    }
+
+    if (size < 0) {
+        qerror_report(QERR_UNDEFINED_ERROR);
+        return -1;
+    }
+
+    if (bdrv_truncate(bs, size)) {
+        qerror_report(QERR_UNDEFINED_ERROR);
+        return -1;
+    }
+
+    return 0;
+}

blockdev.h

@@ -53,5 +53,6 @@ int do_change_block(Monitor *mon, const char *device,
                     const char *filename, const char *fmt);
 int do_drive_del(Monitor *mon, const QDict *qdict, QObject **ret_data);
 int do_snapshot_blkdev(Monitor *mon, const QDict *qdict, QObject **ret_data);
+int do_block_resize(Monitor *mon, const QDict *qdict, QObject **ret_data);
 
 #endif

hmp-commands.hx

@@ -52,6 +52,25 @@ STEXI
 Quit the emulator.
 ETEXI
 
+    {
+        .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,
+    },
+
+STEXI
+@item block_resize
+@findex block_resize
+Resize a block image while a guest is running.  Usually requires guest
+action to see the updated size.  Resize to a lower size is supported,
+but should be used with extreme caution.  Note that this command only
+resizes image files, it can not resize block devices like LVM volumes.
+ETEXI
+
+
     {
         .name       = "eject",
         .args_type  = "force:-f,device: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
 
     {