Re: [PATCH] proc: calculate the correct /proc/<pid> link count

From: Andrew Morton
Date: Wed Jun 04 2008 - 04:41:40 EST


On Tue, 3 Jun 2008 15:16:59 +0200 Vegard Nossum <vegard.nossum@xxxxxxxxx> wrote:

> From: Vegard Nossum <vegard.nossum@xxxxxxxxx>
> Date: Mon, 2 Jun 2008 08:57:45 +0200
> Subject: [PATCH] proc: calculate the correct /proc/<pid> link count
>
> commit e9720acd728a46cb40daa52c99a979f7c4ff195c

Linus gets upset when we refer to commits only by their hash.

I did this:

This patch:

commit e9720acd728a46cb40daa52c99a979f7c4ff195c
Author: Pavel Emelyanov <xemul@xxxxxxxxxx>
Date: Fri Mar 7 11:08:40 2008 -0800

[NET]: Make /proc/net a symlink on /proc/self/net (v3)

introduced a /proc/self/net directory without bumping the corresponding
link count for /proc/self.

> introduced a
> /proc/self/net directory without bumping the corresponding link count
> for /proc/self.
>
> This patch replaces the static link count initializations with a call
> that counts the number of directory entries in the given pid_entry
> table whenever it is instantiated, and thus relieves the burden of
> manually keeping the two in sync.

Seems much saner.

> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index c447e07..334ce46 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -127,6 +127,23 @@ struct pid_entry {
> NULL, &proc_single_file_operations, \
> { .proc_show = &proc_##OTYPE } )
>
> +/* Count the number of hardlinks for the pid_entry table, excluding the .
> + * and .. links. */

Like this:

/*
* Count the number of hardlinks for the pid_entry table, excluding the .
* and .. links.
*/

please.

> +static unsigned int pid_entry_count_dirs(const struct pid_entry *entries,
> + unsigned int n)
> +{
> + unsigned int i;
> + unsigned int count;
> +
> + count = 0;
> + for (i = 0; i < n; ++i) {
> + if (S_ISDIR(entries[i].mode))
> + ++count;
> + }
> +
> + return count;
> +}

I'm unable to correlate the code with the comment. There is nothing in
here which handles . and ..?


> @@ -2585,10 +2602,9 @@ static struct dentry *proc_pid_instantiate(struct inode *dir,
> inode->i_op = &proc_tgid_base_inode_operations;
> inode->i_fop = &proc_tgid_base_operations;
> inode->i_flags|=S_IMMUTABLE;
> - inode->i_nlink = 5;
> -#ifdef CONFIG_SECURITY
> - inode->i_nlink += 1;
> -#endif
> +
> + inode->i_nlink = 2 + pid_entry_count_dirs(tgid_base_stuff,
> + ARRAY_SIZE(tgid_base_stuff));
>

oh, can we do that? Is it possible for some code somewhere to come
along and add a new entry to /proc/pid which doesn't appear in
these static tables?

I guess that doesn't happen. In which case can we not calculate the
unmber of directories in these two tables just a single time, at
bootup?

I think I'm missing things here...
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