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

If the "write" file operation handler, `comedi_write()` is passed 0 for
the amount to write, 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 write of
non-zero length) and the subdevice gets marked as non-busy.

A zero-length write that returns 0 has no other effects, in particular,
it does not cause the subdevice to be marked as non-busy.

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 2015-11-18 17:55:11 +00:00 committed by Greg Kroah-Hartman
parent 3318c7add8
commit 28a60c456b
1 changed files with 4 additions and 3 deletions
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7
drivers/staging/comedi/comedi_fops.c
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@ -2331,8 +2331,6 @@ static ssize_t comedi_write(struct file *file, const char __user *buf,
}
async = s->async;
if (!nbytes)
goto out;
if (s->busy != file || !(async->cmd.flags & CMDF_WRITE)) {
retval = -EINVAL;
goto out;
@ -2349,9 +2347,12 @@ static ssize_t comedi_write(struct file *file, const char __user *buf,
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;
/* Allocate all free buffer space. */
comedi_buf_write_alloc(s, async->prealloc_bufsz);