[PATCH 08/10] staging: comedi: return error on "read" if no command set up

[Ian Abbott]

The "read" file operation handler, `comedi_read()` returns an error for
pretty much any condition that prevents a "read" going ahead.  One of
the conditions that prevents a "read" going ahead is that no
asynchronous command has been set up, but that currently results in a
return value of 0 (unless COMEDI instructions are being processed or an
asynchronous command has been set up by a different file object).
Change it to return `-EINVAL` in this case.

Signed-off-by: Ian Abbott <abbotti@xxxxxxxxx>
---
 drivers/staging/comedi/comedi_fops.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c
index 9505a34..db88fa5 100644
--- a/drivers/staging/comedi/comedi_fops.c
+++ b/drivers/staging/comedi/comedi_fops.c
@@ -2477,8 +2477,12 @@ static ssize_t comedi_read(struct file *file, char __user *buf, size_t nbytes,
 	}
 
 	async = s->async;
-	if (!s->busy || !nbytes)
+	if (!nbytes)
+		goto out;
+	if (!s->busy) {
+		retval = -EINVAL;
 		goto out;
+	}
 	if (s->busy != file) {
 		retval = -EACCES;
 		goto out;
@@ -2516,6 +2520,7 @@ static ssize_t comedi_read(struct file *file, char __user *buf, size_t nbytes,
 				break;
 			}
 			if (!s->busy) {
+				retval = -EINVAL;
 				break;
 			}
 			if (s->busy != file) {
-- 
2.6.1

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