Re: [PATCH V3] seq_file: Document seq_open_private(), seq_release_private()

[Rob Jones]

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@xxxxxxxxxxxxxxx>
> Acked-by: Steven Whitehouse <swhiteho@xxxxxxxxxx>
>
> 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@xxxxxxxxxxxxxxx
tel:+44 161 236 5575
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