From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Marchand <david.marchand@6wind.com>
Subject: Re: [PATCH v5 1/3] contrib: add ivshmem client and server
Date: Fri, 05 Sep 2014 14:07:54 +0200
Message-ID: <5409A79A.8050302@6wind.com>
References: <1409835061-19989-1-git-send-email-david.marchand@6wind.com> <1409835061-19989-2-git-send-email-david.marchand@6wind.com> <20140904155657.GD21203@redhat.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Cc: "qemu-devel@nongnu.org Developers" <qemu-devel@nongnu.org>,
	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>,
	"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>
To: "Michael S. Tsirkin" <mst@redhat.com>
Return-path: <kvm-owner@vger.kernel.org>
Received: from mail-wi0-f178.google.com ([209.85.212.178]:42376 "EHLO
	mail-wi0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S932083AbaIEMIA (ORCPT <rfc822;kvm@vger.kernel.org>);
	Fri, 5 Sep 2014 08:08:00 -0400
Received: by mail-wi0-f178.google.com with SMTP id r20so2848929wiv.11
        for <kvm@vger.kernel.org>; Fri, 05 Sep 2014 05:07:59 -0700 (PDT)
In-Reply-To: <20140904155657.GD21203@redhat.com>
Sender: kvm-owner@vger.kernel.org
List-ID: <kvm.vger.kernel.org>

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