/*
 * Copyright (c) 2014  Hauke Mehrtens <hauke@hauke-m.de>
 *
 * Backport functionality introduced in Linux 3.19.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */
#include <linux/wait.h>
#include <linux/sched.h>
#include <linux/kthread.h>
#include <linux/export.h>
#include <linux/net.h>
#include <linux/netdevice.h>
#include <linux/skbuff.h>
#include <linux/debugfs.h>

#if LINUX_VERSION_CODE < KERNEL_VERSION(3,18,12)
static inline bool is_kthread_should_stop(void)
{
	return (current->flags & PF_KTHREAD) && kthread_should_stop();
}

/*
 * DEFINE_WAIT_FUNC(wait, woken_wake_func);
 *
 * add_wait_queue(&wq, &wait);
 * for (;;) {
 *     if (condition)
 *         break;
 *
 *     p->state = mode;				condition = true;
 *     smp_mb(); // A				smp_wmb(); // C
 *     if (!wait->flags & WQ_FLAG_WOKEN)	wait->flags |= WQ_FLAG_WOKEN;
 *         schedule()				try_to_wake_up();
 *     p->state = TASK_RUNNING;		    ~~~~~~~~~~~~~~~~~~
 *     wait->flags &= ~WQ_FLAG_WOKEN;		condition = true;
 *     smp_mb() // B				smp_wmb(); // C
 *						wait->flags |= WQ_FLAG_WOKEN;
 * }
 * remove_wait_queue(&wq, &wait);
 *
 */
long wait_woken(wait_queue_t *wait, unsigned mode, long timeout)
{
	set_current_state(mode); /* A */
	/*
	 * The above implies an smp_mb(), which matches with the smp_wmb() from
	 * woken_wake_function() such that if we observe WQ_FLAG_WOKEN we must
	 * also observe all state before the wakeup.
	 */
	if (!(wait->flags & WQ_FLAG_WOKEN) && !is_kthread_should_stop())
		timeout = schedule_timeout(timeout);
	__set_current_state(TASK_RUNNING);

	/*
	 * The below implies an smp_mb(), it too pairs with the smp_wmb() from
	 * woken_wake_function() such that we must either observe the wait
	 * condition being true _OR_ WQ_FLAG_WOKEN such that we will not miss
	 * an event.
	 */
	set_mb(wait->flags, wait->flags & ~WQ_FLAG_WOKEN); /* B */

	return timeout;
}
EXPORT_SYMBOL(wait_woken);

int woken_wake_function(wait_queue_t *wait, unsigned mode, int sync, void *key)
{
	/*
	 * Although this function is called under waitqueue lock, LOCK
	 * doesn't imply write barrier and the users expects write
	 * barrier semantics on wakeup functions.  The following
	 * smp_wmb() is equivalent to smp_wmb() in try_to_wake_up()
	 * and is paired with set_mb() in wait_woken().
	 */
	smp_wmb(); /* C */
	wait->flags |= WQ_FLAG_WOKEN;

	return default_wake_function(wait, mode, sync, key);
}
EXPORT_SYMBOL(woken_wake_function);
#endif

#ifdef __BACKPORT_NETDEV_RSS_KEY_FILL
u8 netdev_rss_key[NETDEV_RSS_KEY_LEN];

void netdev_rss_key_fill(void *buffer, size_t len)
{
	BUG_ON(len > sizeof(netdev_rss_key));
	net_get_random_once(netdev_rss_key, sizeof(netdev_rss_key));
	memcpy(buffer, netdev_rss_key, len);
}
EXPORT_SYMBOL_GPL(netdev_rss_key_fill);
#endif /* __BACKPORT_NETDEV_RSS_KEY_FILL */

#if defined(CONFIG_DEBUG_FS)
struct debugfs_devm_entry {
	int (*read)(struct seq_file *seq, void *data);
	struct device *dev;
};

static int debugfs_devm_entry_open(struct inode *inode, struct file *f)
{
	struct debugfs_devm_entry *entry = inode->i_private;

	return single_open(f, entry->read, entry->dev);
}

static const struct file_operations debugfs_devm_entry_ops = {
	.owner = THIS_MODULE,
	.open = debugfs_devm_entry_open,
	.release = single_release,
	.read = seq_read,
	.llseek = seq_lseek
};

/**
 * debugfs_create_devm_seqfile - create a debugfs file that is bound to device.
 *
 * @dev: device related to this debugfs file.
 * @name: name of the debugfs file.
 * @parent: a pointer to the parent dentry for this file.  This should be a
 *	directory dentry if set.  If this parameter is %NULL, then the
 *	file will be created in the root of the debugfs filesystem.
 * @read_fn: function pointer called to print the seq_file content.
 */
struct dentry *debugfs_create_devm_seqfile(struct device *dev, const char *name,
					   struct dentry *parent,
					   int (*read_fn)(struct seq_file *s,
							  void *data))
{
	struct debugfs_devm_entry *entry;

	if (IS_ERR(parent))
		return ERR_PTR(-ENOENT);

	entry = devm_kzalloc(dev, sizeof(*entry), GFP_KERNEL);
	if (!entry)
		return ERR_PTR(-ENOMEM);

	entry->read = read_fn;
	entry->dev = dev;

	return debugfs_create_file(name, S_IRUGO, parent, entry,
				   &debugfs_devm_entry_ops);
}
EXPORT_SYMBOL_GPL(debugfs_create_devm_seqfile);

#endif /* CONFIG_DEBUG_FS */

int skb_ensure_writable(struct sk_buff *skb, int write_len)
{
	if (!pskb_may_pull(skb, write_len))
		return -ENOMEM;

	if (!skb_cloned(skb) || skb_clone_writable(skb, write_len))
		return 0;

	return pskb_expand_head(skb, 0, 0, GFP_ATOMIC);
}
EXPORT_SYMBOL_GPL(skb_ensure_writable);
