Hi Jiri and list,
The HID core has a hid_input_report function which returns an integer,
but all its callers are not really changing their behavior based on the
return value. The few^Wonly exception that does not completely ignore
the return value is the hid-logitech-dj driver which prints a debugging
message.
Should this method be changed to return void? The kerneldoc does not
document its return value anyway.
Confusion 2: the raw_event callback of the hid_driver structure returns
an int, but over time non-negative values are ignored by
hid_input_report. This happened in the following change:
--------------------------------------------------
commit b1a1442a23776756b254b69786848a94d92445ba
Author: Jiri Kosina <jkosina@xxxxxxx>
Date: Mon Jun 3 11:27:48 2013 +0200
HID: core: fix reporting of raw events
hdrw->raw event can return three different return value types:
- ret < 0 indicates that the hdrv driver found an error while parsing
- ret == 0 indicates no error has been encountered, and the driver has
processed the report
- ret > 0 indicates that there was no parsing error, and the driver hasn't
processed the event.
Calling hid_report_raw_event() has to be called appropriately so that it
reflects what has been done by ->raw_event() callback, otherwise we might
updates of the in-kernel structure are lost upon arrival of the report, which
is wrong.
Reported-and-tested-by: Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx>
Reported-and-tested-by: Daniel Leung <daniel.leung@xxxxxxxxxxxxxxx>
Signed-off-by: Jiri Kosina <jkosina@xxxxxxx>
diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
index c272078..8f616bd 100644
--- a/drivers/hid/hid-core.c
+++ b/drivers/hid/hid-core.c
@@ -1293,7 +1293,7 @@ int hid_input_report(struct hid_device *hid, int type, u8 *data, int size, int i
if (hdrv && hdrv->raw_event && hid_match_report(hid, report)) {
ret = hdrv->raw_event(hid, report, data, size);
- if (ret != 0) {
+ if (ret < 0) {
ret = ret < 0 ? ret : 0;
goto unlock;
}
--------------------------------------------------
So now it does not matter whether the raw_event method returns 0 or 1.
The documentation says:
raw_event and event should return 0 on no action performed, 1 when
no further processing should be done and negative on error
What does "no further processing" mean? I guess that the intention was
to signal from a HID driver to ignore the packet, but that the above
change was done to update the state and allow hidraw to pick up the
report.
--
Kind regards,
Peter
https://lekensteyn.nl
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