Re: [PATCH v8] Input: Add userio module

On Fri, Oct 09, 2015 at 10:30:53AM -0400, cpaul@redhat.com wrote:

From: Stephen Chandler Paul <redacted>
+
+static ssize_t userio_char_read(struct file *file, char __user *user_buffer,
+				size_t count, loff_t *ppos)
+{
+	struct userio_device *userio = file->private_data;
+	int ret;
+	size_t nonwrap_len, copylen;
+	unsigned char buf[USERIO_BUFSIZE];
+	unsigned long flags;
+
+	if (!count)
+		return 0;
+
+	/*
+	 * By the time we get here, the data that was waiting might have been
+	 * taken by another thread. Grab the mutex and check if there's still
+	 * any data waiting, otherwise repeat this process until we have data
+	 * (unless the file descriptor is non-blocking of course)
+	 */
+	for (;;) {
+		spin_lock_irqsave(&userio->buf_lock, flags);
+
+		if (userio->head != userio->tail)
+			break;
+
+		spin_unlock_irqrestore(&userio->buf_lock, flags);
+
+		if (file->f_flags & O_NONBLOCK)
+			return -EAGAIN;
+
+		ret = wait_event_interruptible(userio->waitq,
+					       userio->head != userio->tail);
+		if (ret)
+			return ret;
+	}
+
+	nonwrap_len = CIRC_CNT_TO_END(userio->head, userio->tail,
+				      USERIO_BUFSIZE);
+	copylen = min(nonwrap_len, count);
+	memcpy(buf, &userio->buf[userio->tail], copylen);
+
+	userio->tail = (userio->tail + copylen) % USERIO_BUFSIZE;
+
+	spin_unlock_irqrestore(&userio->buf_lock, flags);
+
+	if (copy_to_user(user_buffer, buf, copylen))
+		return -EFAULT;
+
+	return copylen;
+}

Hello

I think you could simplify by just return copy_to_user() since it return copylen in case of success.

Regards