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| author | David Herrmann <dh.herrmann@googlemail.com> | 2012-06-10 15:16:15 +0200 |
|---|---|---|
| committer | Jiri Kosina <jkosina@suse.cz> | 2012-06-18 13:42:00 +0200 |
| commit | 1f9dec1e0164b48da9b268a02197f38caa69b118 (patch) | |
| tree | 3352f158c7173094f84deb1cbad25a9a40122d32 /drivers/hid | |
| parent | HID: uhid: add internal message buffer (diff) | |
| download | linux-1f9dec1e0164b48da9b268a02197f38caa69b118.tar.xz linux-1f9dec1e0164b48da9b268a02197f38caa69b118.zip | |
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>
Diffstat (limited to 'drivers/hid')
| -rw-r--r-- | drivers/hid/uhid.c | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/drivers/hid/uhid.c b/drivers/hid/uhid.c index 05ef4b05a63e..b1a477f8260c 100644 --- a/drivers/hid/uhid.c +++ b/drivers/hid/uhid.c @@ -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; } |