On Fri, Oct 09, 2015 at 10:30:53AM -0400, cpaul@xxxxxxxxxx wrote:
> From: Stephen Chandler Paul <cpaul@xxxxxxxxxx>
> +
> +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
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