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>

diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c
index aced00e..39ed22b 100644 (file)
--- 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;