linux-kernel - Re: [PATCH] proc_fops: convert drivers/isdn/ to seq

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Date:	Mon, 30 Nov 2009 23:17:09 +0300
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	Tilman Schmidt <tilman@...p.cc>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, isdn@...ux-pingi.de, mac@...ware.de
Subject: Re: [PATCH] proc_fops: convert drivers/isdn/ to seq_file

On Mon, Nov 30, 2009 at 01:42:32AM +0100, Tilman Schmidt wrote:
> Am 25.11.2009 05:59 schrieb Alexey Dobriyan:
> > --- a/drivers/isdn/gigaset/capi.c
> > +++ b/drivers/isdn/gigaset/capi.c
> > @@ -2106,35 +2106,22 @@ static char *gigaset_procinfo(struct capi_ctr *ctr)
> >  	return ctr->name;	/* ToDo: more? */
> >  }
> >  
> > -/**
> > - * gigaset_ctr_read_proc() - build controller proc file entry
> > - * @page:	buffer of PAGE_SIZE bytes for receiving the entry.
> > - * @start:	unused.
> > - * @off:	unused.
> > - * @count:	unused.
> > - * @eof:	unused.
> > - * @ctr:	controller descriptor structure.
> > - *
> > - * Return value: length of generated entry
> > - */
> > -static int gigaset_ctr_read_proc(char *page, char **start, off_t off,
> > -			  int count, int *eof, struct capi_ctr *ctr)
> > +static int gigaset_proc_show(struct seq_file *m, void *v)
> 
> I would prefer that, instead of throwing the kerneldoc comment away,
> you adapted it to the new function. Specifically, I would like to
> know what the second argument "void *v" is for.

Sorry, no.
I personally find the corellation between kernel-docness and useleness
to be highly positive.

Comment is removed because after removal of parameters "description",
nothing is left.

> >  {
> > +	struct capi_ctr *ctr = m->private;
> 
> See below.
> 
> > +static int gigaset_proc_open(struct inode *inode, struct file *file)
> > +{
> > +	return single_open(file, gigaset_proc_show, PDE(inode)->data);
> 
> I'd like to understand how that works.
> 
> According to Documentation/filesystems/seq_file.txt, the value of
> the last argument will be passed to the proc_show function in the
> private field of the seq_file structure. Your gigaset_proc_show()
> function assumes that this will be the capi_ctr pointer for the
> device.
> 
> So what is PDE(inode)->data and where does it get set to the
> capi_ctr pointer for the device?

When you create proc entry, you set ->data for proc entry,
it's accessible as PDE(inode)->data.
Now you need to pass it doen to actual hook.
It got stashed eventually into struct seq_file::private (see single_open())
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