Re: [Qemu-devel] [PATCH v5 1/3] contrib: add ivshmem client and server

[David Marchand]

Hello Michael,

On 09/04/2014 05:56 PM, Michael S. Tsirkin wrote:
> > +    /* create the unix listening socket */
> > +    sock_fd = socket(AF_UNIX, SOCK_STREAM, 0);
> > +    if (sock_fd < 0) {
> > +        debug_log(server, "cannot create socket: %s\n", strerror(errno));
> > +        goto err_close_shm;
> > +    }
> > +
> > +    sun.sun_family = AF_UNIX;
> > +    snprintf(sun.sun_path, sizeof(sun.sun_path), "%s", server->unix_sock_path);
> > +    unlink(sun.sun_path);
>
> why unlink it?

Yes, this is wrong, because this means that when starting multiple
servers on the same socket, the last server is the one who wins ...
while I think it should be the opposite (first server wins, as it may
have some connected clients).

I have been scratching my head about this: when should I unlink ?

My current fix unlinks from ivshmem_server_close() (which should be the
right place).
I need to call this when exiting, but I can only do this when the server
exits gracefully (when an error occurs on the server socket or when 
receiving a SIGTERM).

If something unexpected happens (like a bug/crash or a SIGKILL), the
socket won't be unlinked and the next server process will refuse to start.
Is this something acceptable ?

Do you have a better idea ?


Thanks.

--
David Marchand