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

[Kevin Wolf <kwolf@redhat.com>]

Am 24.01.2011 18:44, schrieb Marcelo Tosatti:
> On Mon, Jan 24, 2011 at 01:32:33PM +0100, Christoph Hellwig wrote:
>> 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	2011-01-24 11:55:36.744254374 +0100
>> +++ qemu/hmp-commands.hx	2011-01-24 11:56:23.619254094 +0100
>> @@ -53,6 +53,25 @@ 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",
>>          .params     = "[-f] device",
>> Index: qemu/blockdev.c
>> ===================================================================
>> --- qemu.orig/blockdev.c	2011-01-24 11:56:20.903004129 +0100
>> +++ qemu/blockdev.c	2011-01-24 11:56:38.391254165 +0100
>> @@ -705,3 +705,33 @@ int do_drive_del(Monitor *mon, const QDi
>>  
>>      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;
>> +    }
> 
> Can't resize if block migration is in progress. Don't see a problem 
> with simply disallowing resize in that case.

Then we should add a check to bdrv_truncate.

Kevin