path: root/drivers/hid/uhid.c
diff options
authorDavid Herrmann <dh.herrmann@googlemail.com>2012-06-10 15:16:15 +0200
committerJiri Kosina <jkosina@suse.cz>2012-06-18 13:42:00 +0200
commit1f9dec1e0164b48da9b268a02197f38caa69b118 (patch)
tree3352f158c7173094f84deb1cbad25a9a40122d32 /drivers/hid/uhid.c
parentace3d8614ab0e6544f5f85921085b55b915fe9aa (diff)
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/uhid.c')
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 0;

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