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

The "write" file operation handler, `comedi_write()` returns an error
for pretty much any condition that prevents a "write" going ahead.  One
of the conditions that prevents a "write" 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 4dd42890c6414992c40cc2720a99f0f807713747..2a2b5a06ed0e97bfc8d0cef935f3db7f5ca7eb16 100644 (file)
--- a/drivers/staging/comedi/comedi_fops.c
+++ b/drivers/staging/comedi/comedi_fops.c
@@ -2331,9 +2331,12 @@ static ssize_t comedi_write(struct file *file, const char __user *buf,
        }
 
        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;
@@ -2373,8 +2376,10 @@ static ssize_t comedi_write(struct file *file, const char __user *buf,
                                retval = -ERESTARTSYS;
                                break;
                        }
-                       if (!s->busy)
+                       if (!s->busy) {
+                               retval = -EINVAL;
                                break;
+                       }
                        if (s->busy != file) {
                                retval = -EACCES;
                                break;