Subject: Re: [net-next PATCH v5 2/3] sysctl: add proc_do_large_bitmap

From: Cong Wang <[email-masked]>
Date: Sun, 21 Feb 2010 14:35:02 +0800

Octavian Purdila wrote:
> The new function can be used to read/write large bitmaps via /proc. A
> comma separated range format is used for compact output and input
> (e.g. 1,3-4,10-10).
> 
> Writing into the file will first reset the bitmap then update it
> based on the given input.
> 
> Signed-off-by: Octavian Purdila <[email-masked]>
> Cc: WANG Cong <[email-masked]>
> Cc: Eric W. Biederman <[email-masked]>
> ---
>  include/linux/sysctl.h |    2 +
>  kernel/sysctl.c        |  122 ++++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 124 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
> index f66014c..7bb5cb6 100644
> --- a/include/linux/sysctl.h
> +++ b/include/linux/sysctl.h
> @@ -980,6 +980,8 @@ extern int proc_doulongvec_minmax(struct ctl_table *, int,
>  				  void __user *, size_t *, loff_t *);
>  extern int proc_doulongvec_ms_jiffies_minmax(struct ctl_table *table, int,
>  				      void __user *, size_t *, loff_t *);
> +extern int proc_do_large_bitmap(struct ctl_table *, int,
> +				void __user *, size_t *, loff_t *);
>  
>  /*
>   * Register a set of sysctl names by calling register_sysctl_table
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index 5259727..ef2c13d 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -2635,6 +2635,128 @@ static int proc_do_cad_pid(struct ctl_table *table, int write,
>  	return 0;
>  }
>  
> +/**
> + * proc_do_large_bitmap - read/write from/to a large bitmap
> + * @table: the sysctl table
> + * @write: %TRUE if this is a write to the sysctl file
> + * @buffer: the user buffer
> + * @lenp: the size of the user buffer
> + * @ppos: file position
> + *
> + * The bitmap is stored at table->data and the bitmap length (in bits)
> + * in table->maxlen.
> + *
> + * We use a range comma separated format (e.g. 1,3-4,10-10) so that
> + * large bitmaps may be represented in a compact manner. Writing into
> + * the file will clear the bitmap then update it with the given input.

My test shows it still accepts spaces, e.g.

echo '50000 50003 50005' > ip_local_reserved_ports

works same as

echo '50000,50003,50005' > ip_local_reserved_ports

Is this expected? We will only accept commas, right?

Also, if I write an invalid value, it does reject this, but the previous
value in that file is cleared, shouldn't we keep the previous one?