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Date: Fri, 24 Sep 2010 15:46:28 +0200
From: Daniel Lezcano <dlezcano@fr.ibm.com>
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To: "Eric W. Biederman" <ebiederm@xmission.com>
CC: linux-kernel@vger.kernel.org,
        Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>,
        Pavel Emelyanov <xemul@openvz.org>,
        Pavel Emelyanov <xemul@parallels.com>,
        Ulrich Drepper <drepper@gmail.com>, netdev@vger.kernel.org,
        Jonathan Corbet <corbet@lwn.net>, Jan Engelhardt <jengelh@medozas.de>,
        linux-fsdevel@vger.kernel.org, netfilter-devel@vger.kernel.org,
        Michael Kerrisk <mtk.manpages@gmail.com>,
        Linux Containers <containers@lists.osdl.org>,
        Ben Greear <greearb@candelatech.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        David Miller <davem@davemloft.net>, Al Viro <viro@ZenIV.linux.org.uk>
Subject: Re: [PATCH 7/8] net: Allow setting the network namespace by fd
References: <m1ocborgq7.fsf@fess.ebiederm.org> <m1hbhgq1v1.fsf@fess.ebiederm.org>
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On 09/23/2010 10:51 AM, Eric W. Biederman wrote:
>
> Take advantage of the new abstraction and allow network devices
> to be placed in any network namespace that we have a fd to talk
> about.
>
> Signed-off-by: Eric W. Biederman<ebiederm@xmission.com>
> ---

[ ... ]

> +struct net *get_net_ns_by_fd(int fd)
> +{
> +	struct proc_inode *ei;
> +	struct file *file;
> +	struct net *net;
> +
> +	file = NULL;
> +	net = ERR_PTR(-EINVAL);
> +	file = proc_ns_fget(fd);
> +	if (!fd)
> +		goto out;
> +		return ERR_PTR(-EINVAL);
> +
> +	ei = PROC_I(file->f_dentry->d_inode);
> +	if (ei->ns_ops !=&netns_operations)
> +		goto out;

Is this check necessary here ? proc_ns_fget checks "file->f_op != 
&ns_file_operations", no ?