[Qemu-devel] [PATCH 1/3] block: add resize monitor command

[Christoph Hellwig]

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 <h...@lst.de>

Index: qemu/hmp-commands.hx
===================================================================
--- qemu.orig/hmp-commands.hx   2011-01-14 15:11:48.527004132 +0100
+++ qemu/hmp-commands.hx        2011-01-14 15:40:14.407006506 +0100
@@ -53,6 +53,24 @@ Quit the emulator.
 ETEXI
 
     {
+        .name       = "resize",
+        .args_type  = "id:s,size:l",
+        .params     = "device size",
+        .help       = "resize a block image",
+        .user_print = monitor_user_noop,
+        .mhandler.cmd_new = do_resize,
+    },
+
+STEXI
+@item resize
+@findex resize
+Resize a block image while a guest is running.  Usuaully requires guest
+action to see the updated size.  Resize to a lower size is supported,
+but should be used with extreme caution.
+ETEXI
+
+
+    {
         .name       = "eject",
         .args_type  = "force:-f,device:B",
         .params     = "[-f] device",
Index: qemu/blockdev.c
===================================================================
--- qemu.orig/blockdev.c        2011-01-14 15:11:48.539261151 +0100
+++ qemu/blockdev.c     2011-01-14 15:50:35.604293558 +0100
@@ -700,3 +700,41 @@ int do_drive_del(Monitor *mon, const QDi
 
     return 0;
 }
+
+int do_resize(Monitor *mon, const QDict *qdict, QObject **ret_data)
+{
+    const char *id = qdict_get_str(qdict, "id");
+    int64_t size = qdict_get_int(qdict, "size");
+    BlockDriverState *bs;
+
+    bs = bdrv_find(id);
+    if (!bs) {
+        qerror_report(QERR_DEVICE_NOT_FOUND, id);
+        return -1;
+    }
+
+    if (bdrv_get_type_hint(bs) == BDRV_TYPE_CDROM) {
+        error_report("Can not resize CDROM devices\n");
+        return -1;
+    }
+
+    if (size < 0) {
+        error_report("Can only resize to positive sizes");
+        return -1;
+    }
+
+    switch (bdrv_truncate(bs, size)) {
+    case 0:
+        return 0;
+    case -ENOTSUP:
+        error_report("This image format does not support resize");
+        return -1;
+    case -EACCES:
+        error_report("Image is read-only");
+        return -1;
+    default:
+        error_report("Error resizing image");
+        return -1;
+    }
+}
+
Index: qemu/blockdev.h
===================================================================
--- qemu.orig/blockdev.h        2011-01-14 15:11:48.548263456 +0100
+++ qemu/blockdev.h     2011-01-14 15:12:00.965047363 +0100
@@ -53,5 +53,6 @@ int do_change_block(Monitor *mon, const
                     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_resize(Monitor *mon, const QDict *qdict, QObject **ret_data);
 
 #endif