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HID: uhid: implement feature requests

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HID standard allows sending a feature request to the device which is
answered by an HID report. uhid implements this by sending a UHID_FEATURE
event to user-space which then must answer with UHID_FEATURE_ANSWER. If it
doesn't do this in a timely manner, the request is discarded silently.

We serialize the feature requests, that is, there is always only a single
active feature-request sent to user-space, other requests have to wait.
HIDP and USB-HID do it the same way.

Because we discard feature-requests silently, we must make sure to match
a response to the corresponding request. We use sequence-IDs for this so
user-space must copy the ID from the request into the answer.
Feature-answers are ignored if they do not contain the same ID as the
currently pending feature request.

Internally, we must make sure that feature-requests are synchronized with
UHID_DESTROY and close() events. We must not dead-lock when closing the
HID device, either, so we have to use separate locks.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
This commit is contained in:
David Herrmann
2012-06-10 15:16:25 +02:00
committed by Jiri Kosina
parent 3b3baa82e4
commit fcfcf0deb8
2 changed files with 136 additions and 1 deletions
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17
include/linux/uhid.h
View File

@@ -32,6 +32,8 @@ enum uhid_event_type {
UHID_OUTPUT,
UHID_OUTPUT_EV,
UHID_INPUT,
UHID_FEATURE,
UHID_FEATURE_ANSWER,
};
struct uhid_create_req {
@@ -73,6 +75,19 @@ struct uhid_output_ev_req {
__s32 value;
} __attribute__((__packed__));
struct uhid_feature_req {
__u32 id;
__u8 rnum;
__u8 rtype;
} __attribute__((__packed__));
struct uhid_feature_answer_req {
__u32 id;
__u16 err;
__u16 size;
__u8 data[UHID_DATA_MAX];
};
struct uhid_event {
__u32 type;
@@ -81,6 +96,8 @@ struct uhid_event {
struct uhid_input_req input;
struct uhid_output_req output;
struct uhid_output_ev_req output_ev;
struct uhid_feature_req feature;
struct uhid_feature_answer_req feature_answer;
} u;
} __attribute__((__packed__));