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1f9dec1e01
As long as the internal buffer is not empty, we return POLLIN to user-space. uhid->head and uhid->tail are no atomics so the comparison may return inexact results. However, this doesn't matter here as user-space would need to poll() in two threads simultaneously to trigger this. And in this case it doesn't matter if a cached result is returned or the exact new result as user-space does not know which thread returns first from poll() and the following read(). So it is safe to compare the values without locking. Signed-off-by: David Herrmann <dh.herrmann@googlemail.com> Signed-off-by: Jiri Kosina <jkosina@suse.cz>
161 lines
3.2 KiB
C
161 lines
3.2 KiB
C
/*
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* User-space I/O driver support for HID subsystem
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* Copyright (c) 2012 David Herrmann
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*/
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/*
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* This program is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License as published by the Free
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* Software Foundation; either version 2 of the License, or (at your option)
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* any later version.
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*/
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#include <linux/atomic.h>
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#include <linux/device.h>
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#include <linux/fs.h>
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#include <linux/hid.h>
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#include <linux/input.h>
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#include <linux/miscdevice.h>
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#include <linux/module.h>
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#include <linux/mutex.h>
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#include <linux/poll.h>
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#include <linux/sched.h>
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#include <linux/spinlock.h>
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#include <linux/uhid.h>
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#include <linux/wait.h>
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#define UHID_NAME "uhid"
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#define UHID_BUFSIZE 32
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struct uhid_device {
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struct hid_device *hid;
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wait_queue_head_t waitq;
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spinlock_t qlock;
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__u8 head;
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__u8 tail;
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struct uhid_event *outq[UHID_BUFSIZE];
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};
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static struct miscdevice uhid_misc;
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static void uhid_queue(struct uhid_device *uhid, struct uhid_event *ev)
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{
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__u8 newhead;
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newhead = (uhid->head + 1) % UHID_BUFSIZE;
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if (newhead != uhid->tail) {
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uhid->outq[uhid->head] = ev;
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uhid->head = newhead;
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wake_up_interruptible(&uhid->waitq);
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} else {
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hid_warn(uhid->hid, "Output queue is full\n");
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kfree(ev);
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}
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}
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static int uhid_queue_event(struct uhid_device *uhid, __u32 event)
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{
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unsigned long flags;
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struct uhid_event *ev;
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ev = kzalloc(sizeof(*ev), GFP_KERNEL);
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if (!ev)
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return -ENOMEM;
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ev->type = event;
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spin_lock_irqsave(&uhid->qlock, flags);
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uhid_queue(uhid, ev);
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spin_unlock_irqrestore(&uhid->qlock, flags);
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return 0;
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}
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static int uhid_char_open(struct inode *inode, struct file *file)
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{
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struct uhid_device *uhid;
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uhid = kzalloc(sizeof(*uhid), GFP_KERNEL);
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if (!uhid)
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return -ENOMEM;
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spin_lock_init(&uhid->qlock);
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init_waitqueue_head(&uhid->waitq);
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file->private_data = uhid;
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nonseekable_open(inode, file);
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return 0;
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}
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static int uhid_char_release(struct inode *inode, struct file *file)
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{
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struct uhid_device *uhid = file->private_data;
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unsigned int i;
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for (i = 0; i < UHID_BUFSIZE; ++i)
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kfree(uhid->outq[i]);
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kfree(uhid);
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return 0;
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}
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static ssize_t uhid_char_read(struct file *file, char __user *buffer,
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size_t count, loff_t *ppos)
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{
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return 0;
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}
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static ssize_t uhid_char_write(struct file *file, const char __user *buffer,
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size_t count, loff_t *ppos)
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{
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return 0;
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}
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static unsigned int uhid_char_poll(struct file *file, poll_table *wait)
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{
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struct uhid_device *uhid = file->private_data;
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poll_wait(file, &uhid->waitq, wait);
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if (uhid->head != uhid->tail)
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return POLLIN | POLLRDNORM;
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return 0;
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}
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static const struct file_operations uhid_fops = {
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.owner = THIS_MODULE,
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.open = uhid_char_open,
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.release = uhid_char_release,
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.read = uhid_char_read,
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.write = uhid_char_write,
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.poll = uhid_char_poll,
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.llseek = no_llseek,
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};
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static struct miscdevice uhid_misc = {
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.fops = &uhid_fops,
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.minor = MISC_DYNAMIC_MINOR,
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.name = UHID_NAME,
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};
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static int __init uhid_init(void)
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{
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return misc_register(&uhid_misc);
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}
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static void __exit uhid_exit(void)
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{
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misc_deregister(&uhid_misc);
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}
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module_init(uhid_init);
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module_exit(uhid_exit);
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MODULE_LICENSE("GPL");
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MODULE_AUTHOR("David Herrmann <dh.herrmann@gmail.com>");
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MODULE_DESCRIPTION("User-space I/O driver support for HID subsystem");
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