linux-kernel - Re: [PATCH 04/11] General notification queue with user mmap()'able ring buffer [ver #7]

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Date:   Tue, 03 Sep 2019 17:37:10 +0100
From:   David Howells <dhowells@...hat.com>
To:     Hillf Danton <hdanton@...a.com>
Cc:     dhowells@...hat.com, viro@...iv.linux.org.uk,
        Casey Schaufler <casey@...aufler-ca.com>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        nicolas.dichtel@...nd.com, raven@...maw.net,
        Christian Brauner <christian@...uner.io>,
        keyrings@...r.kernel.org, linux-usb@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-api@...r.kernel.org,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 04/11] General notification queue with user mmap()'able ring buffer [ver #7]

Hillf Danton <hdanton@...a.com> wrote:

> > +	for (i = 0; i < wf->nr_filters; i++) {
> > +		wt = &wf->filters[i];
> > +		if (n->type == wt->type &&
> > +		    (wt->subtype_filter[n->subtype >> 5] &
> > +		     (1U << (n->subtype & 31))) &&
> 
> Replace the pure numbers with something easier to understand.

How about the following:

static bool filter_watch_notification(const struct watch_filter *wf,
				      const struct watch_notification *n)
{
	const struct watch_type_filter *wt;
	unsigned int st_bits = sizeof(wt->subtype_filter[0]) * 8;
	unsigned int st_index = n->subtype / st_bits;
	unsigned int st_bit = 1U << (n->subtype % st_bits);
	int i;

	if (!test_bit(n->type, wf->type_filter))
		return false;

	for (i = 0; i < wf->nr_filters; i++) {
		wt = &wf->filters[i];
		if (n->type == wt->type &&
		    (wt->subtype_filter[st_index] & st_bit) &&
		    (n->info & wt->info_mask) == wt->info_filter)
			return true;
	}

	return false; /* If there is a filter, the default is to reject. */
}

David