[Devel] Re: [PATCH] Rewrite proc seq operations via seq_list_xxx ones

[Mathieu Desnoyers]

* Pavel Emelyanov (xemul at openvz.org) wrote:
> Some time ago I posted a set of patches that consolidated
> the seq files, walking the list_head-s. This set was merged
> in the mm tree. /proc/diskstats and /proc/partitions files 
> were included in this set, but a bit later this part was 
> dropped because of conflicts with some other changes.
> 
> Here's the fixed version against the latest git block repo.
> 

Hi Pavel,

You might want to try implementing this patch on top of the sorted seq
list patch I proposed there. It deals with a race between proc file read
and list modification between iterations.

http://lkml.org/lkml/2007/9/6/175

See this patch for a user implementation example and test code
(/proc/modules) :

http://lkml.org/lkml/2007/9/6/176

Mathieu

> Signed-off-by: Pavel Emelyanov <xemul at openvz.org>
> 
> ---
> 
> diff --git a/block/genhd.c b/block/genhd.c
> index 3af1e7a..27f7061 100644
> --- a/block/genhd.c
> +++ b/block/genhd.c
> @@ -264,39 +264,34 @@ void __init printk_all_partitions(void)
>  
>  #ifdef CONFIG_PROC_FS
>  /* iterator */
> -static void *part_start(struct seq_file *part, loff_t *pos)
> +static void *disk_start(struct seq_file *part, loff_t *pos)
>  {
> -	struct list_head *p;
> -	loff_t l = *pos;
> -
>  	mutex_lock(&block_subsys_lock);
> -	list_for_each(p, &block_subsys.list)
> -		if (!l--)
> -			return list_entry(p, struct gendisk, kobj.entry);
> -	return NULL;
> +	return seq_list_start_head(&block_subsys.list, *pos);
>  }
>  
> -static void *part_next(struct seq_file *part, void *v, loff_t *pos)
> +static void *disk_next(struct seq_file *part, void *v, loff_t *pos)
>  {
> -	struct list_head *p = ((struct gendisk *)v)->kobj.entry.next;
> -	++*pos;
> -	return p==&block_subsys.list ? NULL :
> -		list_entry(p, struct gendisk, kobj.entry);
> +	return seq_list_next(v, &block_subsys.list, pos);
>  }
>  
> -static void part_stop(struct seq_file *part, void *v)
> +static void disk_stop(struct seq_file *part, void *v)
>  {
>  	mutex_unlock(&block_subsys_lock);
>  }
>  
>  static int show_partition(struct seq_file *part, void *v)
>  {
> -	struct gendisk *sgp = v;
> +	struct gendisk *sgp;
>  	int n;
>  	char buf[BDEVNAME_SIZE];
>  
> -	if (&sgp->kobj.entry == block_subsys.list.next)
> +	if (v == &block_subsys.list) {
>  		seq_puts(part, "major minor  #blocks  name\n\n");
> +		return 0;
> +	}
> +
> +	sgp = list_entry(v, struct gendisk, kobj.entry);
>  
>  	/* Don't show non-partitionable removeable devices or empty devices */
>  	if (!get_capacity(sgp) ||
> @@ -325,9 +320,9 @@ static int show_partition(struct seq_fil
>  }
>  
>  struct seq_operations partitions_op = {
> -	.start =part_start,
> -	.next =	part_next,
> -	.stop =	part_stop,
> +	.start =disk_start,
> +	.next =	disk_next,
> +	.stop =	disk_stop,
>  	.show =	show_partition
>  };
>  #endif
> @@ -616,44 +611,22 @@ decl_subsys(block, &ktype_block, &block_
>   */
>  
>  /* iterator */
> -static void *diskstats_start(struct seq_file *part, loff_t *pos)
> -{
> -	loff_t k = *pos;
> -	struct list_head *p;
> -
> -	mutex_lock(&block_subsys_lock);
> -	list_for_each(p, &block_subsys.list)
> -		if (!k--)
> -			return list_entry(p, struct gendisk, kobj.entry);
> -	return NULL;
> -}
> -
> -static void *diskstats_next(struct seq_file *part, void *v, loff_t *pos)
> -{
> -	struct list_head *p = ((struct gendisk *)v)->kobj.entry.next;
> -	++*pos;
> -	return p==&block_subsys.list ? NULL :
> -		list_entry(p, struct gendisk, kobj.entry);
> -}
> -
> -static void diskstats_stop(struct seq_file *part, void *v)
> -{
> -	mutex_unlock(&block_subsys_lock);
> -}
> -
>  static int diskstats_show(struct seq_file *s, void *v)
>  {
> -	struct gendisk *gp = v;
> +	struct gendisk *gp;
>  	char buf[BDEVNAME_SIZE];
>  	int n = 0;
>  
> +	if (v == &block_subsys.list)
>  	/*
> -	if (&sgp->kobj.entry == block_subsys.kset.list.next)
>  		seq_puts(s,	"major minor name"
>  				"     rio rmerge rsect ruse wio wmerge "
>  				"wsect wuse running use aveq"
>  				"\n\n");
>  	*/
> +		return 0;
> +
> +	gp = list_entry(v, struct gendisk, kobj.entry);
>   
>  	preempt_disable();
>  	disk_round_stats(gp);
> @@ -686,9 +659,9 @@ static int diskstats_show(struct seq_fil
>  }
>  
>  struct seq_operations diskstats_op = {
> -	.start	= diskstats_start,
> -	.next	= diskstats_next,
> -	.stop	= diskstats_stop,
> +	.start	= disk_start,
> +	.next	= disk_next,
> +	.stop	= disk_stop,
>  	.show	= diskstats_show
>  };
>  
> -
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-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68