linux-kernel - Re: [PATCH] procfs: fix numbering in /proc/locks

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Message-ID: <4CA0B743.2050801@parallels.com>
Date:	Mon, 27 Sep 2010 19:24:51 +0400
From:	Pavel Emelyanov <xemul@...allels.com>
To:	Jerome Marchand <jmarchan@...hat.com>
CC:	Matthew Wilcox <matthew@....cx>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] procfs: fix numbering in /proc/locks

On 09/27/2010 07:13 PM, Jerome Marchand wrote:
> 
> The lock number in /proc/locks (first field) is implemented by a counter
> (private field of struct seq_file) which is incremented at each call of
> locks_show(). Currently it is reset each time locks_start() is called,
> that is each time we call the read() syscall on /proc/locks. Because of
> that, the numbering erratically restarts at 1 several times when reading
> a long /proc/locks file.
> We want the counter to be initialized at opening time and then never
> reset until we close the file. Fortunately, seq_open() memzeros the
> seq_file structure, so we can just drop the reset in locks_start() and
> move the increment the counter before actually printing the line so the
> numbering still starts at 1.

IMHO the implementation is wrong. If you want the proper sequence number
while file is open you should increase on in the ->next callback of the
seq_ops, not in show.

> Signed-off-by: Jerome Marchand <jmarchan@...hat.com>
> ---
> diff --git a/fs/locks.c b/fs/locks.c
> index ab24d49..a5eab5e 100644
> --- a/fs/locks.c
> +++ b/fs/locks.c
> @@ -2161,19 +2161,18 @@ static int locks_show(struct seq_file *f, void *v)
>  
>  	fl = list_entry(v, struct file_lock, fl_link);
>  
> +	f->private++;
>  	lock_get_status(f, fl, (long)f->private, "");
>  
>  	list_for_each_entry(bfl, &fl->fl_block, fl_block)
>  		lock_get_status(f, bfl, (long)f->private, " ->");
>  
> -	f->private++;
>  	return 0;
>  }
>  
>  static void *locks_start(struct seq_file *f, loff_t *pos)
>  {
>  	lock_kernel();
> -	f->private = (void *)1;
>  	return seq_list_start(&file_lock_list, *pos);
>  }
>  
> 

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