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staging: comedi: check for more errors for zero-length read

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If the "read" file operation handler, `comedi_read()` is passed 0 for
the amount to read, some error conditions are currently skipped and the
function just returns 0.  Change it to check those error conditions and
return an error value if appropriate.  The trickiest case is the check
for when the previously set up asynchronous command has terminated with
an error.  In that case, `-EPIPE` is returned (as it is for a read of
non-zero length) and the subdevice gets marked as non-busy.

A zero-length read that returns 0 has no other effects, in particular,
it does not cause the subdevice to be marked as non-busy, and the return
value does not indicate an "end-of-file" condition.

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>
This commit is contained in:
Ian Abbott 2015-10-12 17:21:29 +01:00 committed by Greg Kroah-Hartman
parent 3958284775
commit 3c3bea26ad
1 changed files with 5 additions and 5 deletions
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10
drivers/staging/comedi/comedi_fops.c
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@ -2478,15 +2478,13 @@ static ssize_t comedi_read(struct file *file, char __user *buf, size_t nbytes,
}
async = s->async;
if (!nbytes)
goto out;
if (s->busy != file || (async->cmd.flags & CMDF_WRITE)) {
retval = -EINVAL;
goto out;
}
add_wait_queue(&async->wait_head, &wait);
while (nbytes > 0 && !retval) {
while (count == 0 && !retval) {
unsigned int rp, n1, n2;
set_current_state(TASK_INTERRUPTIBLE);
@ -2500,9 +2498,12 @@ static ssize_t comedi_read(struct file *file, char __user *buf, size_t nbytes,
if (!comedi_is_runflags_running(runflags)) {
if (comedi_is_runflags_in_error(runflags))
retval = -EPIPE;
become_nonbusy = true;
if (retval || nbytes)
become_nonbusy = true;
break;
}
if (nbytes == 0)
break;
if (file->f_flags & O_NONBLOCK) {
retval = -EAGAIN;
break;
@ -2539,7 +2540,6 @@ static ssize_t comedi_read(struct file *file, char __user *buf, size_t nbytes,
nbytes -= n;
buf += n;
break; /* makes device work like a pipe */
}
remove_wait_queue(&async->wait_head, &wait);
set_current_state(TASK_RUNNING);