Re: [Qemu-devel] [PATCH] Add -f option to qemu-nbd

[Stefan Hajnoczi <stefanha@gmail.com>]

On Wed, Nov 16, 2011 at 11:49 AM, Zhi Yong Wu <zwu.kernel@gmail.com> wrote:
> On Wed, Nov 16, 2011 at 6:34 PM, Stefan Hajnoczi <stefanha@gmail.com> wrote:
>> On Wed, Nov 16, 2011 at 6:57 AM, Chunyan Liu <cyliu@suse.com> wrote:
>>> Currently qemu-nbd does not support finding free nbd device for users like
>>> "losetup -f" and issuing "qemu-nbd -c /dev/nbdX disk.img" won't report error
>>> message when /dev/nbd is already in use. It makes things a little confusing.
>>> This patch adds "-f" option to qemu-nbd to support finding a free nbd device
>>> for users. Please review and share your comments. Thanks.
>>>
>>> Signed-off-by: Chunyan Liu <cyliu@suse.com>
>>> ---
>>>  qemu-nbd.c |   65 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
>>>  1 files changed, 64 insertions(+), 1 deletions(-)
>>
>> This patch finds a free device but does not immediately attach to it
>> and use it.  Interfaces like this are prone to race conditions, I
>> think it would make more sense to combine the -f option with running
>> the actual NBD server.
>>
>> I suggest:
>> qemu-nbd -f disk.img
> Why must we add one new option? I prefer to not adding new option,
> only enhance existing function of qemu-nbd -c disk.img.

That would change the command-line interface and break existing users.
 There might be scripts or tools that call out to qemu-nbd, they would
break if we changed the meaning of -c.

Stefan