[PATCH 2/3] iio: buffer: make sure O_NONBLOCK is respected

["Nuno Sá" <nuno.sa@analog.com>]

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.

Fixes: 9eeee3b0bf190 ("iio: Add output buffer support")
Signed-off-by: Nuno Sá <nuno.sa@analog.com>
---
 drivers/iio/industrialio-buffer.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c
index c56cf748fde1..7e7ee307a3f7 100644
--- a/drivers/iio/industrialio-buffer.c
+++ b/drivers/iio/industrialio-buffer.c
@@ -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;
-- 
2.39.2