If a COMEDI subdevice is busy handling an asynchronous command in the
"read" direction, then after the command has terminated itself, the
"read" file operation handler, `comedi_read()` should keep the subdevice
busy until all available data has been read and it has returned 0 to
indicate an "end-of-file" condition. Currently, it has a bug where it
can mark the subdevice as non-busy even when returning a non-zero count.
The bug is slightly hidden because the next "read" will return 0 because
the subdevice is no longer busy. Fix it by checking the return count is
0 before deciding to mark the subdevice as non-busy.
The call to `comedi_is_subdevice_idle()` is superfluous as the
`become_nonbusy` variable will have been set to `true` when considering
becoming non-busy. Strictly speaking, checking the return count is
superfluous too, as `become_nonbusy` doesn't get set to `true` unless
the count is 0, but check the return count anyway to make the intention
clearer.
Signed-off-by: Ian Abbott <abbo...@mev.co.uk>
---
drivers/staging/comedi/comedi_fops.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/staging/comedi/comedi_fops.c
b/drivers/staging/comedi/comedi_fops.c
index ef4b58b..f533113 100644
--- a/drivers/staging/comedi/comedi_fops.c
+++ b/drivers/staging/comedi/comedi_fops.c
@@ -2550,7 +2550,7 @@ static ssize_t comedi_read(struct file *file, char __user
*buf, size_t nbytes,
}
remove_wait_queue(&async->wait_head, &wait);
set_current_state(TASK_RUNNING);
- if (become_nonbusy || comedi_is_subdevice_idle(s)) {
+ if (become_nonbusy && count == 0) {
struct comedi_subdevice *new_s;
/*
--
2.6.1
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