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@xxxxxxxxxxxxxx>
---
drivers/hid/uhid.c | 120 +++++++++++++++++++++++++++++++++++++++++++++++++-
include/linux/uhid.h | 17 +++++++
2 files changed, 136 insertions(+), 1 deletion(-)
diff --git a/drivers/hid/uhid.c b/drivers/hid/uhid.c
index 421c492..ea560bf 100644
--- a/drivers/hid/uhid.c
+++ b/drivers/hid/uhid.c
@@ -42,6 +42,12 @@ struct uhid_device {
__u8 head;
__u8 tail;
struct uhid_event *outq[UHID_BUFSIZE];
+
+ struct mutex report_lock;
+ wait_queue_head_t report_wait;
+ atomic_t report_done;
+ atomic_t report_id;
+ struct uhid_event report_buf;
};
static struct miscdevice uhid_misc;
@@ -143,7 +149,84 @@ static int uhid_hid_parse(struct hid_device *hid)
static int uhid_hid_get_raw(struct hid_device *hid, unsigned char rnum,
__u8 *buf, size_t count, unsigned char rtype)
{
- return 0;
+ struct uhid_device *uhid = hid->driver_data;
+ __u8 report_type;
+ struct uhid_event *ev;
+ unsigned long flags;
+ int ret;
+ size_t len;
+ struct uhid_feature_answer_req *req;
+
+ if (!uhid->running)
+ return -EIO;
+
+ switch (rtype) {
+ case HID_FEATURE_REPORT:
+ report_type = UHID_FEATURE_REPORT;
+ break;
+ case HID_OUTPUT_REPORT:
+ report_type = UHID_OUTPUT_REPORT;
+ break;
+ case HID_INPUT_REPORT:
+ report_type = UHID_INPUT_REPORT;
+ break;
+ default:
+ return -EINVAL;
+ }
+
+ ret = mutex_lock_interruptible(&uhid->report_lock);
+ if (ret)
+ return ret;
+
+ ev = kzalloc(sizeof(*ev), GFP_KERNEL);
+ if (!ev) {
+ ret = -ENOMEM;
+ goto unlock;
+ }
+
+ spin_lock_irqsave(&uhid->qlock, flags);
+ ev->type = UHID_FEATURE;
+ ev->u.feature.id = atomic_inc_return(&uhid->report_id);
+ ev->u.feature.rnum = rnum;
+ ev->u.feature.rtype = report_type;
+
+ atomic_set(&uhid->report_done, 0);
+ uhid_queue(uhid, ev);
+ spin_unlock_irqrestore(&uhid->qlock, flags);
+
+ ret = wait_event_interruptible_timeout(uhid->report_wait,
+ atomic_read(&uhid->report_done), 5 * HZ);
+
+ /*
+ * Make sure "uhid->running" is cleared on shutdown before
+ * "uhid->report_done" is set.
+ */
+ smp_rmb();
+ if (!ret || !uhid->running) {
+ ret = -EIO;
+ } else if (ret < 0) {
+ ret = -ERESTARTSYS;
+ } else {
+ spin_lock_irqsave(&uhid->qlock, flags);
+ req = &uhid->report_buf.u.feature_answer;
+
+ if (req->err) {
+ ret = -EIO;
+ } else {
+ ret = 0;
+ len = min(count,
+ min_t(size_t, req->size, UHID_DATA_MAX));
+ memcpy(buf, req->data, len);
+ }
+
+ spin_unlock_irqrestore(&uhid->qlock, flags);
+ }
+
+ atomic_set(&uhid->report_done, 1);
+
+unlock:
+ mutex_unlock(&uhid->report_lock);
+ return ret ? ret : len;
}
static int uhid_hid_output_raw(struct hid_device *hid, __u8 *buf, size_t count,
@@ -265,7 +348,11 @@ static int uhid_dev_destroy(struct uhid_device *uhid)
if (!uhid->running)
return -EINVAL;
+ /* clear "running" before setting "report_done" */
uhid->running = false;
+ smp_wmb();
+ atomic_set(&uhid->report_done, 1);
+ wake_up_interruptible(&uhid->report_wait);
hid_destroy_device(uhid->hid);
kfree(uhid->rd_data);
@@ -284,6 +371,31 @@ static int uhid_dev_input(struct uhid_device *uhid, struct uhid_event *ev)
return 0;
}
+static int uhid_dev_feature_answer(struct uhid_device *uhid,
+ struct uhid_event *ev)
+{
+ unsigned long flags;
+
+ if (!uhid->running)
+ return -EINVAL;
+
+ spin_lock_irqsave(&uhid->qlock, flags);
+
+ /* id for old report; drop it silently */
+ if (atomic_read(&uhid->report_id) != ev->u.feature_answer.id)
+ goto unlock;
+ if (atomic_read(&uhid->report_done))
+ goto unlock;
+
+ memcpy(&uhid->report_buf, ev, sizeof(*ev));
+ atomic_set(&uhid->report_done, 1);
+ wake_up_interruptible(&uhid->report_wait);
+
+unlock:
+ spin_unlock_irqrestore(&uhid->qlock, flags);
+ return 0;
+}
+
static int uhid_char_open(struct inode *inode, struct file *file)
{
struct uhid_device *uhid;
@@ -293,9 +405,12 @@ static int uhid_char_open(struct inode *inode, struct file *file)
return -ENOMEM;
mutex_init(&uhid->devlock);
+ mutex_init(&uhid->report_lock);
spin_lock_init(&uhid->qlock);
init_waitqueue_head(&uhid->waitq);
+ init_waitqueue_head(&uhid->report_wait);
uhid->running = false;
+ atomic_set(&uhid->report_done, 1);
file->private_data = uhid;
nonseekable_open(inode, file);
@@ -398,6 +513,9 @@ static ssize_t uhid_char_write(struct file *file, const char __user *buffer,
case UHID_INPUT:
ret = uhid_dev_input(uhid, &uhid->input_buf);
break;
+ case UHID_FEATURE_ANSWER:
+ ret = uhid_dev_feature_answer(uhid, &uhid->input_buf);
+ break;
default:
ret = -EOPNOTSUPP;
}
diff --git a/include/linux/uhid.h b/include/linux/uhid.h
index 2c97255..9c6974f 100644
--- a/include/linux/uhid.h
+++ b/include/linux/uhid.h
@@ -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__));
--
1.7.10.4
--
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