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Date:   Thu, 30 Jul 2020 15:18:34 +0300
From:   Alexey Dobriyan <adobriyan@gmail.com>
To:     Kirill Tkhai <ktkhai@virtuozzo.com>
Cc:     viro@zeniv.linux.org.uk, davem@davemloft.net,
        ebiederm@xmission.com, akpm@linux-foundation.org,
        christian.brauner@ubuntu.com, areber@redhat.com, serge@hallyn.com,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 11/23] fs: Add /proc/namespaces/ directory
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On Thu, Jul 30, 2020 at 03:00:19PM +0300, Kirill Tkhai wrote:

> # ls /proc/namespaces/ -l
> lrwxrwxrwx 1 root root 0 Jul 29 16:50 'cgroup:[4026531835]' -> 'cgroup:[4026531835]'
> lrwxrwxrwx 1 root root 0 Jul 29 16:50 'ipc:[4026531839]' -> 'ipc:[4026531839]'
> lrwxrwxrwx 1 root root 0 Jul 29 16:50 'mnt:[4026531840]' -> 'mnt:[4026531840]'
> lrwxrwxrwx 1 root root 0 Jul 29 16:50 'mnt:[4026531861]' -> 'mnt:[4026531861]'
> lrwxrwxrwx 1 root root 0 Jul 29 16:50 'mnt:[4026532133]' -> 'mnt:[4026532133]'
> lrwxrwxrwx 1 root root 0 Jul 29 16:50 'mnt:[4026532134]' -> 'mnt:[4026532134]'
> lrwxrwxrwx 1 root root 0 Jul 29 16:50 'mnt:[4026532135]' -> 'mnt:[4026532135]'
> lrwxrwxrwx 1 root root 0 Jul 29 16:50 'mnt:[4026532136]' -> 'mnt:[4026532136]'
> lrwxrwxrwx 1 root root 0 Jul 29 16:50 'net:[4026531993]' -> 'net:[4026531993]'
> lrwxrwxrwx 1 root root 0 Jul 29 16:50 'pid:[4026531836]' -> 'pid:[4026531836]'
> lrwxrwxrwx 1 root root 0 Jul 29 16:50 'time:[4026531834]' -> 'time:[4026531834]'
> lrwxrwxrwx 1 root root 0 Jul 29 16:50 'user:[4026531837]' -> 'user:[4026531837]'
> lrwxrwxrwx 1 root root 0 Jul 29 16:50 'uts:[4026531838]' -> 'uts:[4026531838]'

I'd say make it '%s-%llu'. The brackets don't carry any information.
And ':' forces quoting with recent coreutils.

> +static int parse_namespace_dentry_name(const struct dentry *dentry,
> +		const char **type, unsigned int *type_len, unsigned int *inum)
> +{
> +	const char *p, *name;
> +	int count;
> +
> +	*type = name = dentry->d_name.name;
> +	p = strchr(name, ':');
> +	*type_len = p - name;
> +	if (!p || p == name)
> +		return -ENOENT;
> +
> +	p += 1;
> +	if (sscanf(p, "[%u]%n", inum, &count) != 1 || *(p + count) != '\0' ||
> +	    *inum < PROC_NS_MIN_INO)
> +		return -ENOENT;

sscanf is banned from lookup code due to lax whitespace rules.
See

	commit ac7f1061c2c11bb8936b1b6a94cdb48de732f7a4
	proc: fix /proc/*/map_files lookup

Of course someone sneaked in 1 instance, yikes.

	$ grep -e scanf -n -r fs/proc/
	fs/proc/base.c:1596:            err = sscanf(pos, "%9s %lld %lu", clock,

> +static int proc_namespaces_readdir(struct file *file, struct dir_context *ctx)

> +		len = snprintf(name, sizeof(name), "%s:[%u]", ns->ops->name, inum);

[] -- no need.