Staging: comedi: don't write to buffer if command finished

For write(), any data copied to the data buffer after the previously
set up streaming acquisition command has finished won't be used, but a
non-empty write() does not currently return 0 (or -EPIPE on error) after
the command has finished until the data buffer has been filled up.
Change this behavior to return 0 (or -EPIPE) any time after the command
has finished, without bothering to fill up the buffer with more useless
data.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 13 insertions, 10 deletions

diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c
index aced00e5cd10..39ed22b80229 100644
--- a/drivers/staging/comedi/comedi_fops.c
+++ b/drivers/staging/comedi/comedi_fops.c
@@ -1576,6 +1576,19 @@ static ssize_t comedi_write(struct file *file, const char __user *buf,
         while (nbytes > 0 && !retval) {
                 set_current_state(TASK_INTERRUPTIBLE);
 
+                if (!(comedi_get_subdevice_runflags(s) & SRF_RUNNING)) {
+                        if (count == 0) {
+                                if (comedi_get_subdevice_runflags(s) &
+                                        SRF_ERROR) {
+                                        retval = -EPIPE;
+                                } else {
+                                        retval = 0;
+                                }
+                                do_become_nonbusy(dev, s);
+                        }
+                        break;
+                }
+
                 n = nbytes;
 
                 m = n;
@@ -1588,16 +1601,6 @@ static ssize_t comedi_write(struct file *file, const char __user *buf,
                         n = m;
 
                 if (n == 0) {
-                        if (!(comedi_get_subdevice_runflags(s) & SRF_RUNNING)) {
-                                if (comedi_get_subdevice_runflags(s) &
-                                    SRF_ERROR) {
-                                        retval = -EPIPE;
-                                } else {
-                                        retval = 0;
-                                }
-                                do_become_nonbusy(dev, s);
-                                break;
-                        }
                         if (file->f_flags & O_NONBLOCK) {
                                 retval = -EAGAIN;
                                 break;