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

[Kevin Wolf <kwolf@redhat.com>]

Am 14.01.2011 17:20, schrieb 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 <hch@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",

size should be 'o' instead of 'l'. The latter may be too small on 32 bit
hosts and doesn't support convenient suffixes:

 * 'l'          target long (32 or 64 bit)

 * 'o'          octets (aka bytes)
 *              user mode accepts an optional T, t, G, g, M, m, K, k
 *              suffix, which multiplies the value by 2^40 for
 *              suffixes T and t, 2^30 for suffixes G and g, 2^20 for
 *              M and m, 2^10 for K and k

> +        .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;
> +    }

Hm, is there a real reason except that CD-ROMs are read-only? The code
below seems to take read-only devices into account.

Kevin