[PATCH] staging: comedi: comedidev.h: Document usage of 'detach' handler

From: Ian Abbott
Date: Thu Dec 08 2016 - 08:53:33 EST

Document when the "detach" handler function pointed to by the `detach`
member of a `struct comedi_driver` is called by the comedi core, and how
the "attach" and "auto_attach" handlers can defer clean-up to it when
they return an error to the comedi core. This is already mentioned as
part of the documentation for `comedi_auto_config()`, but is useful to
document it for `struct comedi_driver` as well, since
`comedi_auto_config()` is not usually called directly by low-level
comedi drivers, and it is not called at all for "legacy" comedi devices
that are configured manually.

Signed-off-by: Ian Abbott <abbotti@xxxxxxxxx>
drivers/staging/comedi/comedidev.h | 12 ++++++++++++
1 file changed, 12 insertions(+)

diff --git a/drivers/staging/comedi/comedidev.h b/drivers/staging/comedi/comedidev.h
index dcb6376..0c7c37a 100644
--- a/drivers/staging/comedi/comedidev.h
+++ b/drivers/staging/comedi/comedidev.h
@@ -426,6 +426,18 @@ enum comedi_cb {
* handler will be called with the COMEDI device structure's board_ptr member
* pointing to the matched pointer to a board name within the driver's private
* array of static, read-only board type information.
+ *
+ * The @detach handler has two roles. If a COMEDI device was successfully
+ * configured by the @attach or @auto_attach handler, it is called when the
+ * device is being deconfigured (by the %COMEDI_DEVCONFIG ioctl, or due to
+ * unloading of the driver, or due to device removal). It is also called when
+ * the @attach or @auto_attach handler returns an error. Therefore, the
+ * @attach or @auto_attach handlers can defer clean-up on error until the
+ * @detach handler is called. If the @attach or @auto_attach handlers free
+ * any resources themselves, they must prevent the @detach handler from
+ * freeing the same resources. The @detach handler must not assume that all
+ * resources requested by the @attach or @auto_attach handler were
+ * successfully allocated.
struct comedi_driver {
/* private: */