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

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Date:	Fri, 27 Jul 2012 07:48:28 +0400
From:	Pavel Emelyanov <xemul@...allels.com>
To:	Cyrill Gorcunov <gorcunov@...nvz.org>
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

> +static int prep_fdinfo_driver(struct proc_fdinfo_extra *extra)
> +{
> +	struct proc_fdinfo_driver *s;
> +
> +	down_read(&fdinfo_drivers_sem);
> +	list_for_each_entry(s, &fdinfo_drivers, list) {
> +		if (s->probe(extra->f_file)) {
> +			extra->driver = s;
> +			break;
> +		}
> +	}
> +	up_read(&fdinfo_drivers_sem);
> +
> +	return 0;
> +}

Maybe a simple list of file_operations:seq_operations mappings would be simpler?

> +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?

Thanks,
Pavel
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