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Date: Wed, 16 Nov 2011 14:27:47 +0000
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From: Stefan Hajnoczi <stefanha@gmail.com>
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Subject: Re: [Qemu-devel] [PATCH] Add -f option to qemu-nbd
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To: Zhi Yong Wu <zwu.kernel@gmail.com>
Cc: Chunyan Liu <cyliu@suse.com>, qemu-devel@nongnu.org

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> wro=
te:
>> 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 l=
ike
>>> "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 confu=
sing.
>>> This patch adds "-f" option to qemu-nbd to support finding a free nbd d=
evice
>>> for users. Please review and share your comments. Thanks.
>>>
>>> Signed-off-by: Chunyan Liu <cyliu@suse.com>
>>> ---
>>> =A0qemu-nbd.c | =A0 65 ++++++++++++++++++++++++++++++++++++++++++++++++=
+++++++++++-
>>> =A01 files changed, 64 insertions(+), 1 deletions(-)
>>
>> This patch finds a free device but does not immediately attach to it
>> and use it. =A0Interfaces 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