linux-kernel - Re: [PATCH V3] seq_file: Document seq_open_private(), seq_release

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Date:	Tue, 26 Aug 2014 11:58:58 +0100
From:	Rob Jones <rob.jones@...ethink.co.uk>
To:	Steven Whitehouse <swhiteho@...hat.com>,
	linux-fsdevel@...r.kernel.org
CC:	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-kernel@...ts.codethink.co.uk, viro@...IV.linux.org.uk,
	ebiederm@...ssion.com, ian.molton@...ethink.co.uk
Subject: Re: [PATCH V3] seq_file: Document seq_open_private(), seq_release_private()

Are there any other responses on this please? It seems pretty
uncontentious. Maybe everyone was at LinuxCon last week.

On 18/08/14 12:50, Steven Whitehouse wrote:
> Hi,
>
> On 18/08/14 12:40, 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>
> Acked-by: Steven Whitehouse <swhiteho@...hat.com>
>
> Steve.
>
>> ---
>>   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..420fc0d 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() called
>> 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));
>> +    }
>> +
>> +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));
>> +
>> +        if (!p)
>> +            return -ENOMEM;
>> +
>> +        p->foo = bar; /* initialize my stuff */
>> +            ...
>> +        p->baz = true;
>> +
>> +        return 0;
>> +    }
>> +
>> +A corresponding close function, seq_release_private() is available which
>> +frees the memory allocated in the corresponding open.
>> +
>>   The other operations of interest - read(), llseek(), and release() -
>> are
>>   all implemented by the seq_file code itself. So a virtual file's
>>   file_operations structure will look like:
>
>
>

-- 
Rob Jones
Codethink Ltd
mailto:rob.jones@...ethink.co.uk
tel:+44 161 236 5575
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