When receiving messages from the HID subsystem, we need to process them
and store them in an internal buffer so user-space can read() on the char
device to retrieve the messages.
This adds a static buffer for 32 messages to each uhid device. Each
message is dynamically allocated so the uhid_device structure does not get
too big.
uhid_queue() adds a message to the buffer. If the buffer is full, the
message is discarded. uhid_queue_event() is an helper for messages without
payload.
This also adds a public header: uhid.h. It contains the declarations for
the user-space API. It is built around "struct uhid_event" which contains
a type field which specifies the event type and each event can then add a
variable-length payload. For now, there is only a dummy event but later
patches will add new event types and payloads.
Signed-off-by: David Herrmann <dh.herrmann@xxxxxxxxxxxxxx>
---
drivers/hid/uhid.c | 65 ++++++++++++++++++++++++++++++++++++++++++++++++++
include/linux/Kbuild | 1 +
include/linux/uhid.h | 33 +++++++++++++++++++++++++
3 files changed, 99 insertions(+)
create mode 100644 include/linux/uhid.h
diff --git a/drivers/hid/uhid.c b/drivers/hid/uhid.c
index 5b02d6c..05ef4b0 100644
--- a/drivers/hid/uhid.c
+++ b/drivers/hid/uhid.c
@@ -25,16 +25,81 @@
#include <linux/wait.h>
#define UHID_NAME "uhid"
+#define UHID_BUFSIZE 32
+
+struct uhid_device {
+ struct hid_device *hid;
+
+ wait_queue_head_t waitq;
+ spinlock_t qlock;
+ __u8 head;
+ __u8 tail;
+ struct uhid_event *outq[UHID_BUFSIZE];
+};
static struct miscdevice uhid_misc;
+static void uhid_queue(struct uhid_device *uhid, struct uhid_event *ev)
+{
+ __u8 newhead;
+
+ newhead = (uhid->head + 1) % UHID_BUFSIZE;
+
+ if (newhead != uhid->tail) {
+ uhid->outq[uhid->head] = ev;
+ uhid->head = newhead;
+ wake_up_interruptible(&uhid->waitq);
+ } else {
+ hid_warn(uhid->hid, "Output queue is full\n");
+ kfree(ev);
+ }
+}
+
+static int uhid_queue_event(struct uhid_device *uhid, __u32 event)
+{
+ unsigned long flags;
+ struct uhid_event *ev;
+
+ ev = kzalloc(sizeof(*ev), GFP_KERNEL);
+ if (!ev)
+ return -ENOMEM;
+
+ ev->type = event;
+
+ spin_lock_irqsave(&uhid->qlock, flags);
+ uhid_queue(uhid, ev);
+ spin_unlock_irqrestore(&uhid->qlock, flags);
+
+ return 0;
+}
+
static int uhid_char_open(struct inode *inode, struct file *file)
{
+ struct uhid_device *uhid;
+
+ uhid = kzalloc(sizeof(*uhid), GFP_KERNEL);
+ if (!uhid)
+ return -ENOMEM;
+
+ spin_lock_init(&uhid->qlock);
+ init_waitqueue_head(&uhid->waitq);
+
+ file->private_data = uhid;
+ nonseekable_open(inode, file);
+
return 0;
}
static int uhid_char_release(struct inode *inode, struct file *file)
{
+ struct uhid_device *uhid = file->private_data;
+ unsigned int i;
+
+ for (i = 0; i < UHID_BUFSIZE; ++i)
+ kfree(uhid->outq[i]);
+
+ kfree(uhid);
+
return 0;
}
diff --git a/include/linux/Kbuild b/include/linux/Kbuild
index 3973783..8cdabec 100644
--- a/include/linux/Kbuild
+++ b/include/linux/Kbuild
@@ -373,6 +373,7 @@ header-y += tty.h
header-y += types.h
header-y += udf_fs_i.h
header-y += udp.h
+header-y += uhid.h
header-y += uinput.h
header-y += uio.h
header-y += ultrasound.h
diff --git a/include/linux/uhid.h b/include/linux/uhid.h
new file mode 100644
index 0000000..16b786a
--- /dev/null
+++ b/include/linux/uhid.h
@@ -0,0 +1,33 @@
+#ifndef __UHID_H_
+#define __UHID_H_
+
+/*
+ * User-space I/O driver support for HID subsystem
+ * Copyright (c) 2012 David Herrmann
+ */
+
+/*
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation; either version 2 of the License, or (at your option)
+ * any later version.
+ */
+
+/*
+ * Public header for user-space communication. We try to keep every structure
+ * aligned but to be safe we also use __attribute__((__packed__)). Therefore,
+ * the communication should be ABI compatible even between architectures.
+ */
+
+#include <linux/input.h>
+#include <linux/types.h>
+
+enum uhid_event_type {
+ UHID_DUMMY,
+};
+
+struct uhid_event {
+ __u32 type;
+} __attribute__((__packed__));
+
+#endif /* __UHID_H_ */
--
1.7.10.4
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