linux-kernel - Re: [kvm-devel] [PATCH/RFC 1/2] anon-inodes: Remove fd_install() from anon_inode

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Message-ID: <47CE68BE.7000201@qumranet.com>
Date:	Wed, 05 Mar 2008 11:32:46 +0200
From:	Avi Kivity <avi@...ranet.com>
To:	Davide Libenzi <davidel@...ilserver.org>
CC:	Roland Dreier <rdreier@...co.com>, kvm-devel@...ts.sourceforge.net,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Al Viro <viro@....linux.org.uk>, linux-fsdevel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Hellwig <hch@....de>
Subject: Re: [kvm-devel] [PATCH/RFC 1/2] anon-inodes: Remove fd_install()
 from anon_inode_getfd()

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.

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