Re: [Qemu-devel] [PATCH v2 0/5] Do not set SO_REUSEADDR on Windows

[Sebastian Ottlik <ottlik@fzi.de>]

On 04.09.2013 19:08, Sebastian Ottlik wrote:
> This patchset disabels all use of SO_REUSEADDR on Windows. On Windows systems
> the default behaviour is equivalent to SO_REUSEADDR on other operating
> systems. SO_REUSEADDR can still be set but results in undesired behaviour
> instead. It may even lead to situations were system behaviour is
> unspecified. More information on this can be found at:
> http://msdn.microsoft.com/en-us/library/windows/desktop/ms740621.aspx
>
> I originally encountered this issue when accidentally launching two QEMU
> instances with identical GDB ports at the same time. In which case QEMU won't
> fail as one might expect.
>
> v2 Changes:
>
> - Introduce a function with os specific implementation instead of using #ifdef
>    I named it socket_set_fast_reuse instead of the suggested qemu_set_reuseaddr
>    so the name better reflects what the function actually does.
>
>   gdbstub.c              |    6 ++----
>   include/qemu/sockets.h |    1 +
>   net/socket.c           |   19 +++++++------------
>   slirp/misc.c           |    3 +--
>   slirp/socket.c         |    4 +---
>   slirp/tcp_subr.c       |    6 ++----
>   slirp/udp.c            |    4 ++--
>   util/oslib-posix.c     |   14 ++++++++++++++
>   util/oslib-win32.c     |   10 ++++++++++
>   util/qemu-sockets.c    |    6 +++---
>   10 files changed, 43 insertions(+), 30 deletions(-)
>
>
> util: add socket_set_fast_reuse function
> gdbstub: call socket_set_fast_reuse instead of setting SO_REUSEADDR
> net: call socket_set_fast_reuse instead of setting SO_REUSEADDR
> slirp: call socket_set_fast_reuse instead of setting SO_REUSEADDR
> util: call socket_set_fast_reuse instead of setting SO_REUSEADDR
>

Pinging this patch, as I think it is still an appropriate approach to 
the issue:

I did some research and apparently there is a valid use case for 
SO_REUSEADDR
on windows when multiple clients need to listen to the same port for the 
same
multicast group. IMHO making qemu_setsockopt ignore SO_REUSEADDR on windows
might be confusing for some use cases. Actually net_socket_mcast_create in
net/socket.c should probably set SO_REUSEADDR on windows. This is also 
an issue
with patch 3 I supplied that I will address in a new version of this 
patch set if there is
an agreement on a general approach.

It was also suggested to introduce a qemu_stream_listen_socket, but I do 
not see a
clear advantage of this approach over the one taken in my patches. To my
understanding there also may be situations where one would like to 
enable fast reuse
of client sockets (i.e. those used with connect()).

Best Regards,
    Sebastian