linux-kernel - Re: [PATCH] seq_file: Document seq_open_private(), seq_release

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Date:	Mon, 11 Aug 2014 13:05:51 +0100
From:	Ben Hutchings <ben.hutchings@...ethink.co.uk>
To:	Rob Jones <rob.jones@...ethink.co.uk>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...ts.codethink.co.uk,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	ebiederm@...ssion.com, swhiteho@...hat.com, viro@...IV.linux.org.uk
Subject: Re: [PATCH] seq_file: Document seq_open_private(),
 seq_release_private()

On Thu, 2014-08-07 at 15:51 +0100, Rob Jones wrote:
> Despite the fact that these functions have been around for years, they are
> little used (only 15 uses in 13 files at the preseht time) even though
> many other files use work-arounds to achieve the same result.
> 
> By documenting them, hopefully they will become more widely used.
> 
> Signed-off-by: Rob Jones <rob.jones@...ethink.co.uk>
> ---
>  Documentation/filesystems/seq_file.txt |   33 ++++++++++++++++++++++++++++++++
>  1 file changed, 33 insertions(+)
> 
> diff --git a/Documentation/filesystems/seq_file.txt b/Documentation/filesystems/seq_file.txt
> index a1e2e0d..c9b8f6b 100644
> --- a/Documentation/filesystems/seq_file.txt
> +++ b/Documentation/filesystems/seq_file.txt
> @@ -226,6 +226,39 @@ be used for more than one file, you can store an arbitrary pointer in the
>  private field of the seq_file structure; that value can then be retrieved
>  by the iterator functions.
>  
> +There is also a wrapper function to seq_open(), seq_open_private(). It
> +kmallocs a zero filled block of memory and stores a pointer to it in the
> +private field of the seq_file structure, returning 0 on success. The
> +block size is specified in a third parameter to the function, e.g.:
> +
> +	static int ct_open(struct inode *inode, struct file *file)
> +	{
> +		return seq_open_private(file, &ct_seq_ops,
> +					sizeof(struct mystruct);

Missing close-parenthesis.

> +	}
> +
> +There is also a variant function, __seq_open_private(), which is functionally
> +identical except that, if successful, it returns the pointer to the allocated
> +memory block, allowing further initialisation e.g.:
> +
> +	static int ct_open(struct inode *inode, struct file *file)
> +	{
> +		struct mystruct *p =
> +			__seq_open_private(file, &ct_seq_ops, sizeof(*p);
[...]

and here.

Ben.


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