staging: comedi: check command direction in poll() file operation

`comedi_poll()` handles the poll() file operation for comedi devices.

If no asynchronous command has been set up on the current "read"
subdevice, it sets the `POLLIN` and `POLLRDNORM` bits in the return
value to indicate that the read() file operation would not block as it
would return an error.  Add a check so it also does that if the
asynchronous command has been set up in the "write" direction as that
also causes the read() file operation to return an error.

Similarly, if no asynchronous command has need set up on the current
"write" subdevice, it sets the `POLLOUT` and `POLLWRNORM` bits in the
return value to indicate that the write() file operation would not block
as it would return an error.  Add a check so it also does that if the
asynchronous command has been set up in the "read" direction as that
also causes the write() file operation to return an error.

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 0ed6f1f00e7fc875fdb7e9c8775478c60ed709ef..63afd78441f182396077e737df57119c8bffb103 100644 (file)
--- a/drivers/staging/comedi/comedi_fops.c
+++ b/drivers/staging/comedi/comedi_fops.c
@@ -2017,6 +2017,7 @@ static unsigned int comedi_poll(struct file *file, poll_table *wait)
        if (s && s->async) {
                poll_wait(file, &s->async->wait_head, wait);
                if (!s->busy || !comedi_is_subdevice_running(s) ||
+                   (s->async->cmd.flags & CMDF_WRITE) ||
                    comedi_buf_read_n_available(s) > 0)
                        mask |= POLLIN | POLLRDNORM;
        }
@@ -2028,6 +2029,7 @@ static unsigned int comedi_poll(struct file *file, poll_table *wait)
                poll_wait(file, &s->async->wait_head, wait);
                comedi_buf_write_alloc(s, s->async->prealloc_bufsz);
                if (!s->busy || !comedi_is_subdevice_running(s) ||
+                   !(s->async->cmd.flags & CMDF_WRITE) ||
                    comedi_buf_write_n_allocated(s) >= bps)
                        mask |= POLLOUT | POLLWRNORM;
        }