From: David Herrmann <dh.herrmann@googlemail.com>
Date: Sun, 10 Jun 2012 13:16:15 +0000 (+0200)
Subject: HID: uhid: allow poll()'ing on uhid devices
X-Git-Tag: v3.6-rc1~119^2^2~15
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=1f9dec1e0164b48da9b268a02197f38caa69b118;p=pandora-kernel.git

HID: uhid: allow poll()'ing on uhid devices

As long as the internal buffer is not empty, we return POLLIN to
user-space.

uhid->head and uhid->tail are no atomics so the comparison may return
inexact results. However, this doesn't matter here as user-space would
need to poll() in two threads simultaneously to trigger this. And in this
case it doesn't matter if a cached result is returned or the exact new
result as user-space does not know which thread returns first from poll()
and the following read(). So it is safe to compare the values without
locking.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
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