linux-kernel - Re: [patch 3/7] procfs: Add ability to plug in auxiliary fdinfo providers

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Message-ID: <20120727062310.GC21246@moon>
Date:	Fri, 27 Jul 2012 10:23:10 +0400
From:	Cyrill Gorcunov <gorcunov@...nvz.org>
To:	Pavel Emelyanov <xemul@...allels.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	James Bottomley <jbottomley@...allels.com>,
	Matthew Helsley <matt.helsley@...il.com>
Subject: Re: [patch 3/7] procfs: Add ability to plug in auxiliary fdinfo
 providers

On Fri, Jul 27, 2012 at 10:08:38AM +0400, Pavel Emelyanov wrote:
> >>> +static void *seq_next(struct seq_file *m, void *p, loff_t *pos)
> >>> +{
> >>> +	struct proc_fdinfo_extra *extra = m->private;
> >>> +	void *v = NULL;
> >>> +
> >>> +	if (extra->driver) {
> >>> +		int ret = 0;
> >>> +
> >>> +		if (*pos == 0) {
> >>> +			v = extra->driver->ops->start(m, pos);
> >>> +			if (v) {
> >>> +				ret = extra->driver->ops->show(m, v);
> >>
> >> Why is it necessary to call ->show here? The logic should be
> >>
> >> seq_start = (pos == 0 ? nop : extra->start)
> >> seq_next  = (pos == 0 ? extra->start : extra->next)
> >> seq_stop  = (pos == 0 ? nop : extra->stop)
> >> seq_show  = (pos == 0 ? proc_show : extra->show)
> >>
> >> Or I'm missing something?
> > 
> > Well, I thought about it as two sequences -- first is procfs
> > seq-file, which prints out a general header, and second
> > is extra fdinfo provider.
> > 
> > Everything starts with printing procfs header
> > 
> > seq_start -> seq_show (prints "pos:\t%lli\nflags:\t0%o\n") ->
> > seq_next -> (if have extra driver we do extra's start/show at first,
> 
> Why show? The generic seq_file.c will call ->next (which will result in
> extra->start), then ->show (which _should_ result in extra->show) thus
> providing correct output.

Yes, indeed i think i've made it more complex than it should be.
Will update, thanks!

	Cyrill
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