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

[Zhi Yong Wu <zwu.kernel@gmail.com>]

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 way it is safe to execute multiple qemu-nbd -f at the same time
> without race conditions.  Plus it probably makes the user's life
> easier than having to say qemu-nbd -c $(qemu-nbd -f) disk.img.
>
> Stefan
>
>



-- 
Regards,

Zhi Yong Wu