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Date: Fri, 25 Sep 2015 19:56:54 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: linux-api@vger.kernel.org, containers@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org, Roman Gushchin <klamm@yandex-team.ru>,
        Serge Hallyn <serge.hallyn@ubuntu.com>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Chen Fan <chen.fan.fnst@cn.fujitsu.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        =?iso-8859-1?Q?St=E9phane?= Graber <stgraber@ubuntu.com>
Subject: [PATCH 0/1] ns: introduce proc_get_ns_by_fd()
Message-ID: <20150925175654.GA12504@redhat.com>
References: <20150925135246.27620.97496.stgit@buzz>
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On 09/25, Konstantin Khlebnikov wrote:
>
> +struct ns_common *proc_ns_fdget(int fd, int nstype, struct fd *fd_ref)
>  {
> -	struct file *file;
> +	struct ns_common *ns;
> +	struct fd f;
>  
> -	file = fget(fd);
> -	if (!file)
> +	f = fdget(fd);
> +	if (!f.file)
>  		return ERR_PTR(-EBADF);
>  
> -	if (file->f_op != &ns_file_operations)
> +	if (f.file->f_op != &ns_file_operations)
> +		goto out_invalid;
> +
> +	ns = get_proc_ns(file_inode(f.file));
> +	if (nstype && (ns->ops->type != nstype))
>  		goto out_invalid;
>  
> -	return file;
> +	*fd_ref = f;
> +	return ns;
>  
>  out_invalid:
> -	fput(file);
> +	fdput(f);
>  	return ERR_PTR(-EINVAL);
>  }

Well yes, fdget() makes sense but this is minor.

Honestly, I do not really like the new helper... I understand this
is subjective, so I won't insist. But how about 1/1? We do not need
fd/file at all. With this patch your sys_getvpid() can just use
proc_get_ns_by_fd(fd, CLONE_NEWPID) and put_pid_ns().

Eric, what do you think?

See also "TODO" in the changelog.

Oleg.