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: David Herrmann <dh.herrmann@googlemail.com> Signed-off-by: Jiri Kosina <jkosina@suse.cz>
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@ -28,6 +28,7 @@
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#define UHID_BUFSIZE 32
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struct uhid_device {
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struct mutex devlock;
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struct hid_device *hid;
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wait_queue_head_t waitq;
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@ -81,6 +82,7 @@ static int uhid_char_open(struct inode *inode, struct file *file)
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if (!uhid)
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return -ENOMEM;
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mutex_init(&uhid->devlock);
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spin_lock_init(&uhid->qlock);
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init_waitqueue_head(&uhid->waitq);
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@ -106,7 +108,49 @@ static int uhid_char_release(struct inode *inode, struct file *file)
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static ssize_t uhid_char_read(struct file *file, char __user *buffer,
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size_t count, loff_t *ppos)
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{
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return 0;
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struct uhid_device *uhid = file->private_data;
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int ret;
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unsigned long flags;
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size_t len;
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/* they need at least the "type" member of uhid_event */
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if (count < sizeof(__u32))
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return -EINVAL;
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try_again:
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if (file->f_flags & O_NONBLOCK) {
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if (uhid->head == uhid->tail)
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return -EAGAIN;
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} else {
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ret = wait_event_interruptible(uhid->waitq,
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uhid->head != uhid->tail);
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if (ret)
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return ret;
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}
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ret = mutex_lock_interruptible(&uhid->devlock);
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if (ret)
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return ret;
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if (uhid->head == uhid->tail) {
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mutex_unlock(&uhid->devlock);
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goto try_again;
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} else {
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len = min(count, sizeof(**uhid->outq));
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if (copy_to_user(buffer, &uhid->outq[uhid->tail], len)) {
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ret = -EFAULT;
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} else {
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kfree(uhid->outq[uhid->tail]);
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uhid->outq[uhid->tail] = NULL;
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spin_lock_irqsave(&uhid->qlock, flags);
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uhid->tail = (uhid->tail + 1) % UHID_BUFSIZE;
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spin_unlock_irqrestore(&uhid->qlock, flags);
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}
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}
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mutex_unlock(&uhid->devlock);
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return ret ? ret : len;
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}
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static ssize_t uhid_char_write(struct file *file, const char __user *buffer,
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