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Date: Fri, 05 Sep 2014 14:07:54 +0200
From: David Marchand <david.marchand@6wind.com>
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Subject: Re: [Qemu-devel] [PATCH v5 1/3] contrib: add ivshmem client and
	server
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To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Olivier Matz <olivier.matz@6wind.com>, kvm <kvm@vger.kernel.org>, Stefan Hajnoczi <stefanha@gmail.com>, Claudio Fontana <claudio.fontana@huawei.com>, Markus Armbruster <armbru@redhat.com>, "qemu-devel@nongnu.org Developers" <qemu-devel@nongnu.org>, "Gonglei (Arei)" <arei.gonglei@huawei.com>, Martin Kletzander <mkletzan@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, Jani Kokkonen <jani.kokkonen@huawei.com>, Cam Macdonell <cam@cs.ualberta.ca>

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