staging: comedi: check actual data direction for COMEDI_BUFINFO ioctl

`do_bufinfo_ioctl()` handled the `COMEDI_BUFINFO` ioctl.  It is supposed
to update the read or write positions in the buffer depending on the
direction of data transfer set up by the asynchronous command.
Currently it checks the `SDF_CMD_READ` and `SDF_CMD_WRITE` subdevice
flags.  That's fine for most subdevices - the ones that only support one
direction, but is incorrect for those subdevices that allow the command
to be set up in either direction.  Since we now set the `CMDF_WRITE`
flag according to the data transfer direction of the current command
running on the subdevice, check that flag instead.
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>

drivers/staging/comedi/comedi_fops.c

@@ -991,7 +991,7 @@ static int do_bufinfo_ioctl(struct comedi_device *dev,
 	if (s->busy != file)
 		return -EACCES;
 
-	if (bi.bytes_read && (s->subdev_flags & SDF_CMD_READ)) {
+	if (bi.bytes_read && !(async->cmd.flags & CMDF_WRITE)) {
 		bi.bytes_read = comedi_buf_read_alloc(s, bi.bytes_read);
 		comedi_buf_read_free(s, bi.bytes_read);
 
@@ -1001,7 +1001,7 @@ static int do_bufinfo_ioctl(struct comedi_device *dev,
 		}
 	}
 
-	if (bi.bytes_written && (s->subdev_flags & SDF_CMD_WRITE)) {
+	if (bi.bytes_written && (async->cmd.flags & CMDF_WRITE)) {
 		bi.bytes_written =
 		    comedi_buf_write_alloc(s, bi.bytes_written);
 		comedi_buf_write_free(s, bi.bytes_written);