staging: comedi: check for more errors for zero-length write
authorIan Abbott <abbotti@mev.co.uk>
Wed, 18 Nov 2015 17:55:11 +0000 (17:55 +0000)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Mon, 21 Dec 2015 23:58:54 +0000 (15:58 -0800)
commit28a60c456bc52bbe949ad54c6b23917a651fc342
treeeaa3f586fbbc24ad1b44e0a3dd2c494c1b2f700b
parent3318c7add8b43a071498a973548dd24b55c587d4
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>
drivers/staging/comedi/comedi_fops.c