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Commit ace3d861 authored by David Herrmann's avatar David Herrmann Committed by Jiri Kosina
Browse files

HID: uhid: add internal message buffer 



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: default avatarDavid Herrmann <dh.herrmann@googlemail.com>
Signed-off-by: default avatarJiri Kosina <jkosina@suse.cz>
parent 1ccd7a2a

drivers/hid/uhid.c

+65 −0
Original line number Diff line number Diff line
@@ -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;

}

include/linux/Kbuild

+1 −0
Original line number Diff line number Diff line
@@ -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

include/linux/uhid.h

0 → 100644
+33 −0
Original line number Diff line number Diff line 
#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_ */