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Commit d937ae5f authored by David Herrmann's avatar David Herrmann Committed by Jiri Kosina
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HID: uhid: implement read() on uhid devices 



User-space can use read() to get a single event from uhid devices. read()
does never return multiple events. This allows us to extend the event
structure and still keep backwards compatibility.

If user-space wants to get multiple events in one syscall, they should use
the readv()/writev() syscalls which are supported by uhid.

This introduces a new lock which helps us synchronizing simultaneous reads
from user-space. We also correctly return -EINVAL/-EFAULT only on errors
and retry the read() when some other thread captured the event faster than
we did.

Signed-off-by: default avatarDavid Herrmann <dh.herrmann@googlemail.com>
Signed-off-by: default avatarJiri Kosina <jkosina@suse.cz>
parent 1f9dec1e

drivers/hid/uhid.c

+45 −1
Original line number Diff line number Diff line
@@ -28,6 +28,7 @@ 
#define UHID_BUFSIZE	32



struct uhid_device {

	struct mutex devlock;

	struct hid_device *hid;



	wait_queue_head_t waitq;
@@ -81,6 +82,7 @@ static int uhid_char_open(struct inode *inode, struct file *file) 
	if (!uhid)

		return -ENOMEM;



	mutex_init(&uhid->devlock);

	spin_lock_init(&uhid->qlock);

	init_waitqueue_head(&uhid->waitq);
@@ -106,7 +108,49 @@ static int uhid_char_release(struct inode *inode, struct file *file) 
static ssize_t uhid_char_read(struct file *file, char __user *buffer,

				size_t count, loff_t *ppos)

{

	return 0;

	struct uhid_device *uhid = file->private_data;

	int ret;

	unsigned long flags;

	size_t len;



	/* they need at least the "type" member of uhid_event */

	if (count < sizeof(__u32))

		return -EINVAL;



try_again:

	if (file->f_flags & O_NONBLOCK) {

		if (uhid->head == uhid->tail)

			return -EAGAIN;

	} else {

		ret = wait_event_interruptible(uhid->waitq,

						uhid->head != uhid->tail);

		if (ret)

			return ret;

	}



	ret = mutex_lock_interruptible(&uhid->devlock);

	if (ret)

		return ret;



	if (uhid->head == uhid->tail) {

		mutex_unlock(&uhid->devlock);

		goto try_again;

	} else {

		len = min(count, sizeof(**uhid->outq));

		if (copy_to_user(buffer, &uhid->outq[uhid->tail], len)) {

			ret = -EFAULT;

		} else {

			kfree(uhid->outq[uhid->tail]);

			uhid->outq[uhid->tail] = NULL;



			spin_lock_irqsave(&uhid->qlock, flags);

			uhid->tail = (uhid->tail + 1) % UHID_BUFSIZE;

			spin_unlock_irqrestore(&uhid->qlock, flags);

		}

	}



	mutex_unlock(&uhid->devlock);

	return ret ? ret : len;

}



static ssize_t uhid_char_write(struct file *file, const char __user *buffer,