Re: [Qemu-devel] [PATCH v2 1/1] qemu-nbd: add the option to use pre-created server socket

[Denis V. Lunev]

On 10/04/2016 02:09 PM, Daniel P. Berrange wrote:
> On Tue, Oct 04, 2016 at 02:03:01PM +0300, Denis V. Lunev wrote:
>> From: Denis Plotnikov <address@hidden>
>>
>> The NBD server socket was created by qemu-nbd code. This could lead to the
>> race issue when the management layer started qemu-nbd server and allowed
>> a client to connect to the server, the client tried to connect to the
>> server but failed because qemu-nbd had not managed to open the listening
>> server socket by the time the client has finished its trying to connect.
>>
>> Creating a listening socket before starting of qemu-ndb and passing the
>> socket fd to be used as the server socket to qemu-nbd as an option solves
>> this issue.
>>
>> It also helps to resolve the situation when qemu-nbd started by some
>> management software should report the port number qemu-nbd bound to, to
>> another piece of software. Right now, there is no good way to do that
>> except to start the qemu-nbd to make sure that the certain port has been
>> actually aquired. Otherwise, it is definitely racy to try to define the
>> port first and then start the qemu-nbd, hoping that the port defined is
>> still available. Passing of the pre-created file descriptor resolves this
>> situation as well.
>>
>> As a plus, pre-creating of the server socket adds some degree of freedom in
>> setting of the socket properties. It is so, because once qemu-nbd gets
>> the socket fd, it starts using it as is, without any additional
>> modifications.
>>
>> Signed-off-by: Denis Plotnikov <address@hidden>
>> Reviewed-by: Roman Kagan <address@hidden>
>> Signed-off-by: Denis V. Lunev <address@hidden>
>> CC: Paolo Bonzini <address@hidden>
>> ---
>>  qemu-nbd.c    | 95 
>> +++++++++++++++++++++++++++++++++++++++++++++++++++--------
>>  qemu-nbd.texi |  6 ++++
>>  2 files changed, 89 insertions(+), 12 deletions(-)
>>
>> Changes from v1:
>> - commit message improvements
>> - Eric's style nits applied
> It seems you've ignored the suggestion to implement the systemd socket
> activation protocol, which would avoid the need for any new command
> line parameters, and would let qemu-nbd "just work" with systemd units
> too.
>
>
> Regards,
> Daniel
thank you very much. I have missed that letter.
Pls disregard this sending.

ya, we will start over ;)

Den