staging: comedi: return error on "read" if no command set up

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@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c
index 88ba0b6..190592a 100644 (file)
--- a/drivers/staging/comedi/comedi_fops.c
+++ b/drivers/staging/comedi/comedi_fops.c
@@ -2478,8 +2478,12 @@ 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;
@@ -2517,6 +2521,7 @@ 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) {