patch "iio: buffer: make sure O_NONBLOCK is respected" added to char-misc-linus

This is a note to let you know that I've just added the patch titled

iio: buffer: make sure O_NONBLOCK is respected

to my char-misc git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git
in the char-misc-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

From 3da1814184582ed0faf039275a3f02e6f69944ee Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Nuno=20S=C3=A1?= <[email protected]>
Date: Thu, 16 Feb 2023 11:14:51 +0100
Subject: iio: buffer: make sure O_NONBLOCK is respected
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

For output buffers, there's no guarantee that the buffer won't be full in the first iteration of the loop in which case we would block independently of userspace passing O_NONBLOCK or not. Fix it by always checking the flag before going to sleep.

While at it (and as it's a bit related), refactored the loop so that the stop condition is 'written != n', i.e, run the loop until all data has been copied into the IIO buffers. This makes the code a bit simpler.

---
 drivers/iio/industrialio-buffer.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

index 6340d8e1430b..a7a080bed180 100644
@@ -203,21 +203,24 @@ static ssize_t iio_buffer_write(struct file *filp, const char __user *buf,
 				break;
 			}
 
+			if (filp->f_flags & O_NONBLOCK) {
+				if (!written)
+					ret = -EAGAIN;
+				break;
+			}
+
 			wait_woken(&wait, TASK_INTERRUPTIBLE,
 					MAX_SCHEDULE_TIMEOUT);
 			continue;
 		}
 
 		ret = rb->access->write(rb, n - written, buf + written);
-		if (ret == 0 && (filp->f_flags & O_NONBLOCK))
-			ret = -EAGAIN;
+		if (ret < 0)
+			break;
 
-		if (ret > 0) {
-			written += ret;
-			if (written != n && !(filp->f_flags & O_NONBLOCK))
-				continue;
-		}
-	} while (ret == 0);
+		written += ret;
+
+	} while (written != n);
 	remove_wait_queue(&rb->pollq, &wait);
 
 	return ret < 0 ? ret : written;

2.40.0