From mboxrd@z Thu Jan  1 00:00:00 1970
From: Avi Kivity <avi@qumranet.com>
Subject: Re: [PATCH/RFC 1/2] anon-inodes: Remove fd_install()
 from anon_inode_getfd()
Date: Wed, 05 Mar 2008 11:32:46 +0200
Message-ID: <47CE68BE.7000201@qumranet.com>
References: <20080225191043.GA32342@lst.de>
	<adak5kqyzv1.fsf@cisco.com>	<Pine.LNX.4.64.0802271138170.377@alien.or.mcafeemobile.com>	<adabq62yx5r.fsf@cisco.com>	<Pine.LNX.4.64.0802271218210.377@alien.or.mcafeemobile.com>	<ada7igqyurw.fsf@cisco.com>
	<adar6eyx8y5.fsf@cisco.com>	<Pine.LNX.4.64.0802281150060.7660@alien.or.mcafeemobile.com>	<adabq60x20d.fsf@cisco.com>
	<Pine.LNX.4.64.0802281245580.7660@alien.or.mcafeemobile.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Cc: kvm-devel@lists.sourceforge.net,
	Roland Dreier <rdreier@cisco.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Al Viro <viro@ftp.linux.org.uk>, linux-fsdevel@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>,
	Christoph Hellwig <hch@lst.de>
To: Davide Libenzi <davidel@xmailserver.org>
Return-path: <kvm-devel-bounces@lists.sourceforge.net>
In-Reply-To: <Pine.LNX.4.64.0802281245580.7660@alien.or.mcafeemobile.com>
List-Unsubscribe: <https://lists.sourceforge.net/lists/listinfo/kvm-devel>,
	<mailto:kvm-devel-request@lists.sourceforge.net?subject=unsubscribe>
List-Archive: <http://sourceforge.net/mailarchive/forum.php?forum_name=kvm-devel>
List-Post: <mailto:kvm-devel@lists.sourceforge.net>
List-Help: <mailto:kvm-devel-request@lists.sourceforge.net?subject=help>
List-Subscribe: <https://lists.sourceforge.net/lists/listinfo/kvm-devel>,
	<mailto:kvm-devel-request@lists.sourceforge.net?subject=subscribe>
Sender: kvm-devel-bounces@lists.sourceforge.net
Errors-To: kvm-devel-bounces@lists.sourceforge.net
List-Id: linux-fsdevel.vger.kernel.org

Davide Libenzi wrote:
>> I think that may be a bit cleaner than Al's approach, but it still
>> leaves the same trap that create_vcpu_fd() falls into.  The current
>> code is:
>>
>> static int create_vcpu_fd(struct kvm_vcpu *vcpu)
>> {
>> 	int fd, r;
>> 	struct inode *inode;
>> 	struct file *file;
>>
>> 	r = anon_inode_getfd(&fd, &inode, &file,
>> 			     "kvm-vcpu", &kvm_vcpu_fops, vcpu);
>> 	if (r)
>> 		return r;
>> 	atomic_inc(&vcpu->kvm->filp->f_count);
>> 	return fd;
>> }
>>
>> and with your proposal, the natural way to write that becomes:
>>
>> static int create_vcpu_fd(struct kvm_vcpu *vcpu)
>> {
>> 	int fd, r;
>>
>> 	r = anon_inode_getfd(&fd, NULL,
>> 			     "kvm-vcpu", &kvm_vcpu_fops, vcpu);
>> 	if (r)
>> 		return r;
>> 	atomic_inc(&vcpu->kvm->filp->f_count);
>> 	return fd;
>> }
>>     
>
> I don't know KVM code, but can't the "private_data" setup be completed 
> before calling anon_inode_getfd()?
>   

Creating the fd is the last thing done when creating a vcpu.

> Or ...
>
> static int create_vcpu_fd(struct kvm_vcpu *vcpu)
> {
> 	int fd, r;
>
> 	get_file(vcpu->kvm->filp);
> 	r = anon_inode_getfd(&fd, NULL,
> 			     "kvm-vcpu", &kvm_vcpu_fops, vcpu);
> 	if (r) {
> 		fput(vcpu->kvm->filp);
> 		return r;
> 	}
> 	return fd;
> }
>   

This seems reasonable.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.


-------------------------------------------------------------------------
This SF.net email is sponsored by: Microsoft
Defy all challenges. Microsoft(R) Visual Studio 2008.
http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/