From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([208.118.235.92]:59886)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <kwolf@redhat.com>) id 1SwSGT-0007pH-JG
	for qemu-devel@nongnu.org; Wed, 01 Aug 2012 02:18:38 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <kwolf@redhat.com>) id 1SwSGS-0004T4-GY
	for qemu-devel@nongnu.org; Wed, 01 Aug 2012 02:18:37 -0400
Received: from mx1.redhat.com ([209.132.183.28]:17377)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <kwolf@redhat.com>) id 1SwSGS-0004Sy-8Q
	for qemu-devel@nongnu.org; Wed, 01 Aug 2012 02:18:36 -0400
Message-ID: <5018CA31.8050800@redhat.com>
Date: Wed, 01 Aug 2012 08:18:25 +0200
From: Kevin Wolf <kwolf@redhat.com>
MIME-Version: 1.0
References: <20120730213409.21536.7589.sendpatchset@skannery.in.ibm.com>
	<20120730213437.21536.87232.sendpatchset@skannery.in.ibm.com>
	<50181314.1040909@redhat.com>
In-Reply-To: <50181314.1040909@redhat.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Subject: Re: [Qemu-devel] [v2 Patch 2/9]block: raw-posix image file reopen
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Eric Blake <eblake@redhat.com>
Cc: Supriya Kannery <supriyak@linux.vnet.ibm.com>, Shrinidhi Joshi <spjoshi31@gmail.com>, Stefan Hajnoczi <stefanha@gmail.com>, Jeff Cody <jcody@redhat.com>, Corey Bryant <coreyb@linux.vnet.ibm.com>, qemu-devel@nongnu.org, Luiz Capitulino <lcapitulino@redhat.com>, Christoph Hellwig <hch@lst.de>

Am 31.07.2012 19:17, schrieb Eric Blake:
> On 07/30/2012 03:34 PM, Supriya Kannery wrote:
>> raw-posix driver changes for bdrv_reopen_xx functions to
>> safely reopen image files. Reopening of image files while 
>> changing hostcache dynamically is handled here.
>>
>> Signed-off-by: Supriya Kannery <supriyak@linux.vnet.ibm.com>
>>
>> ---
>> Index: qemu/block/raw.c
>> ===================================================================
> 
>> +static int raw_reopen_prepare(BlockDriverState *bs, BDRVReopenState **prs,
>> +                              int flags)
>> +{
>> +    BDRVRawReopenState *raw_rs = g_malloc0(sizeof(BDRVRawReopenState));
>> +    BDRVRawState *s = bs->opaque;
>> +    int ret = 0;
>> +
>> +    raw_rs->reopen_state.bs = bs;
>> +
>> +    /* stash state before reopen */
>> +    raw_rs->stash_s = g_malloc0(sizeof(BDRVRawState));
>> +    raw_stash_state(raw_rs->stash_s, s);
>> +    s->fd = dup3(raw_rs->stash_s->fd, s->fd, O_CLOEXEC);
> 
> You called it out in your cover letter, but just pointing out that this
> is one of the locations that needs a conditional fallback to
> dup2/qemu_set_cloexec if dup3 and O_CLOEXEC are missing.
> 
> More importantly, though, you want this to be fcntl(F_DUP_CLOEXEC) and
> NOT dup3, so that you are duplicating to the first available fd rather
> than accidentally overwriting whatever s->fd happened to be on entry.
> Also, where is your error checking that you didn't just assign s->fd to
> -1?  It looks like your goal here is to stash a copy of the fd, so that
> on failure you can then pivot over to your copy.

Doesn't Corey's fd passing series introduce a helper function for
F_DUP_CLOEXEC and emulation if it isn't support? Could be reused here then.

Kevin