Commit 1f9dec1e authored Jun 10, 2012 by David Herrmann Committed by Jiri Kosina Jun 18, 2012

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>

parent ace3d861

drivers/hid/uhid.c

+7 −0

Original line number	Diff line number	Diff line
		@@ -117,6 +117,13 @@ static ssize_t uhid_char_write(struct file file, const char __user buffer,

		static unsigned int uhid_char_poll(struct file file, poll_table wait)
		{
		struct uhid_device *uhid = file->private_data;

		poll_wait(file, &uhid->waitq, wait);

		if (uhid->head != uhid->tail)
		return POLLIN \| POLLRDNORM;

		return 0;
		}