[PATCH 6/7] staging: comedi: check command direction in poll() file operation

[Ian Abbott]

`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@xxxxxxxxx>
---
 drivers/staging/comedi/comedi_fops.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c
index 6328965..d55f709 100644
--- 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;
 	}
-- 
2.1.1

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/