1 files changed, 407 insertions, 0 deletions
diff --git a/lib/klist.c b/lib/klist.c
new file mode 100644
index 000000000..332a4fbf1
--- /dev/null
+++ b/lib/klist.c
@@ -0,0 +1,407 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * klist.c - Routines for manipulating klists.
+ *
+ * Copyright (C) 2005 Patrick Mochel
+ *
+ * This klist interface provides a couple of structures that wrap around
+ * struct list_head to provide explicit list "head" (struct klist) and list
+ * "node" (struct klist_node) objects. For struct klist, a spinlock is
+ * included that protects access to the actual list itself. struct
+ * klist_node provides a pointer to the klist that owns it and a kref
+ * reference count that indicates the number of current users of that node
+ * in the list.
+ *
+ * The entire point is to provide an interface for iterating over a list
+ * that is safe and allows for modification of the list during the
+ * iteration (e.g. insertion and removal), including modification of the
+ * current node on the list.
+ *
+ * It works using a 3rd object type - struct klist_iter - that is declared
+ * and initialized before an iteration. klist_next() is used to acquire the
+ * next element in the list. It returns NULL if there are no more items.
+ * Internally, that routine takes the klist's lock, decrements the
+ * reference count of the previous klist_node and increments the count of
+ * the next klist_node. It then drops the lock and returns.
+ *
+ * There are primitives for adding and removing nodes to/from a klist.
+ * When deleting, klist_del() will simply decrement the reference count.
+ * Only when the count goes to 0 is the node removed from the list.
+ * klist_remove() will try to delete the node from the list and block until
+ * it is actually removed. This is useful for objects (like devices) that
+ * have been removed from the system and must be freed (but must wait until
+ * all accessors have finished).
+ */
+
+#include <linux/klist.h>
+#include <linux/export.h>
+#include <linux/sched.h>
+
+/*
+ * Use the lowest bit of n_klist to mark deleted nodes and exclude
+ * dead ones from iteration.
+ */
+#define KNODE_DEAD		1LU
+#define KNODE_KLIST_MASK	~KNODE_DEAD
+
+static struct klist *knode_klist(struct klist_node *knode)
+{
+	return (struct klist *)
+		((unsigned long)knode->n_klist & KNODE_KLIST_MASK);
+}
+
+static bool knode_dead(struct klist_node *knode)
+{
+	return (unsigned long)knode->n_klist & KNODE_DEAD;
+}
+
+static void knode_set_klist(struct klist_node *knode, struct klist *klist)
+{
+	knode->n_klist = klist;
+	/* no knode deserves to start its life dead */
+	WARN_ON(knode_dead(knode));
+}
+
+static void knode_kill(struct klist_node *knode)
+{
+	/* and no knode should die twice ever either, see we're very humane */
+	WARN_ON(knode_dead(knode));
+	*(unsigned long *)&knode->n_klist |= KNODE_DEAD;
+}
+
+/**
+ * klist_init - Initialize a klist structure.
+ * @k: The klist we're initializing.
+ * @get: The get function for the embedding object (NULL if none)
+ * @put: The put function for the embedding object (NULL if none)
+ *
+ * Initialises the klist structure.  If the klist_node structures are
+ * going to be embedded in refcounted objects (necessary for safe
+ * deletion) then the get/put arguments are used to initialise
+ * functions that take and release references on the embedding
+ * objects.
+ */
+void klist_init(struct klist *k, void (*get)(struct klist_node *),
+		void (*put)(struct klist_node *))
+{
+	INIT_LIST_HEAD(&k->k_list);
+	spin_lock_init(&k->k_lock);
+	k->get = get;
+	k->put = put;
+}
+EXPORT_SYMBOL_GPL(klist_init);
+
+static void add_head(struct klist *k, struct klist_node *n)
+{
+	spin_lock(&k->k_lock);
+	list_add(&n->n_node, &k->k_list);
+	spin_unlock(&k->k_lock);
+}
+
+static void add_tail(struct klist *k, struct klist_node *n)
+{
+	spin_lock(&k->k_lock);
+	list_add_tail(&n->n_node, &k->k_list);
+	spin_unlock(&k->k_lock);
+}
+
+static void klist_node_init(struct klist *k, struct klist_node *n)
+{
+	INIT_LIST_HEAD(&n->n_node);
+	kref_init(&n->n_ref);
+	knode_set_klist(n, k);
+	if (k->get)
+		k->get(n);
+}
+
+/**
+ * klist_add_head - Initialize a klist_node and add it to front.
+ * @n: node we're adding.
+ * @k: klist it's going on.
+ */
+void klist_add_head(struct klist_node *n, struct klist *k)
+{
+	klist_node_init(k, n);
+	add_head(k, n);
+}
+EXPORT_SYMBOL_GPL(klist_add_head);
+
+/**
+ * klist_add_tail - Initialize a klist_node and add it to back.
+ * @n: node we're adding.
+ * @k: klist it's going on.
+ */
+void klist_add_tail(struct klist_node *n, struct klist *k)
+{
+	klist_node_init(k, n);
+	add_tail(k, n);
+}
+EXPORT_SYMBOL_GPL(klist_add_tail);
+
+/**
+ * klist_add_behind - Init a klist_node and add it after an existing node
+ * @n: node we're adding.
+ * @pos: node to put @n after
+ */
+void klist_add_behind(struct klist_node *n, struct klist_node *pos)
+{
+	struct klist *k = knode_klist(pos);
+
+	klist_node_init(k, n);
+	spin_lock(&k->k_lock);
+	list_add(&n->n_node, &pos->n_node);
+	spin_unlock(&k->k_lock);
+}
+EXPORT_SYMBOL_GPL(klist_add_behind);
+
+/**
+ * klist_add_before - Init a klist_node and add it before an existing node
+ * @n: node we're adding.
+ * @pos: node to put @n after
+ */
+void klist_add_before(struct klist_node *n, struct klist_node *pos)
+{
+	struct klist *k = knode_klist(pos);
+
+	klist_node_init(k, n);
+	spin_lock(&k->k_lock);
+	list_add_tail(&n->n_node, &pos->n_node);
+	spin_unlock(&k->k_lock);
+}
+EXPORT_SYMBOL_GPL(klist_add_before);
+
+struct klist_waiter {
+	struct list_head list;
+	struct klist_node *node;
+	struct task_struct *process;
+	int woken;
+};
+
+static DEFINE_SPINLOCK(klist_remove_lock);
+static LIST_HEAD(klist_remove_waiters);
+
+static void klist_release(struct kref *kref)
+{
+	struct klist_waiter *waiter, *tmp;
+	struct klist_node *n = container_of(kref, struct klist_node, n_ref);
+
+	WARN_ON(!knode_dead(n));
+	list_del(&n->n_node);
+	spin_lock(&klist_remove_lock);
+	list_for_each_entry_safe(waiter, tmp, &klist_remove_waiters, list) {
+		if (waiter->node != n)
+			continue;
+
+		list_del(&waiter->list);
+		waiter->woken = 1;
+		mb();
+		wake_up_process(waiter->process);
+	}
+	spin_unlock(&klist_remove_lock);
+	knode_set_klist(n, NULL);
+}
+
+static int klist_dec_and_del(struct klist_node *n)
+{
+	return kref_put(&n->n_ref, klist_release);
+}
+
+static void klist_put(struct klist_node *n, bool kill)
+{
+	struct klist *k = knode_klist(n);
+	void (*put)(struct klist_node *) = k->put;
+
+	spin_lock(&k->k_lock);
+	if (kill)
+		knode_kill(n);
+	if (!klist_dec_and_del(n))
+		put = NULL;
+	spin_unlock(&k->k_lock);
+	if (put)
+		put(n);
+}
+
+/**
+ * klist_del - Decrement the reference count of node and try to remove.
+ * @n: node we're deleting.
+ */
+void klist_del(struct klist_node *n)
+{
+	klist_put(n, true);
+}
+EXPORT_SYMBOL_GPL(klist_del);
+
+/**
+ * klist_remove - Decrement the refcount of node and wait for it to go away.
+ * @n: node we're removing.
+ */
+void klist_remove(struct klist_node *n)
+{
+	struct klist_waiter waiter;
+
+	waiter.node = n;
+	waiter.process = current;
+	waiter.woken = 0;
+	spin_lock(&klist_remove_lock);
+	list_add(&waiter.list, &klist_remove_waiters);
+	spin_unlock(&klist_remove_lock);
+
+	klist_del(n);
+
+	for (;;) {
+		set_current_state(TASK_UNINTERRUPTIBLE);
+		if (waiter.woken)
+			break;
+		schedule();
+	}
+	__set_current_state(TASK_RUNNING);
+}
+EXPORT_SYMBOL_GPL(klist_remove);
+
+/**
+ * klist_node_attached - Say whether a node is bound to a list or not.
+ * @n: Node that we're testing.
+ */
+int klist_node_attached(struct klist_node *n)
+{
+	return (n->n_klist != NULL);
+}
+EXPORT_SYMBOL_GPL(klist_node_attached);
+
+/**
+ * klist_iter_init_node - Initialize a klist_iter structure.
+ * @k: klist we're iterating.
+ * @i: klist_iter we're filling.
+ * @n: node to start with.
+ *
+ * Similar to klist_iter_init(), but starts the action off with @n,
+ * instead of with the list head.
+ */
+void klist_iter_init_node(struct klist *k, struct klist_iter *i,
+			  struct klist_node *n)
+{
+	i->i_klist = k;
+	i->i_cur = NULL;
+	if (n && kref_get_unless_zero(&n->n_ref))
+		i->i_cur = n;
+}
+EXPORT_SYMBOL_GPL(klist_iter_init_node);
+
+/**
+ * klist_iter_init - Iniitalize a klist_iter structure.
+ * @k: klist we're iterating.
+ * @i: klist_iter structure we're filling.
+ *
+ * Similar to klist_iter_init_node(), but start with the list head.
+ */
+void klist_iter_init(struct klist *k, struct klist_iter *i)
+{
+	klist_iter_init_node(k, i, NULL);
+}
+EXPORT_SYMBOL_GPL(klist_iter_init);
+
+/**
+ * klist_iter_exit - Finish a list iteration.
+ * @i: Iterator structure.
+ *
+ * Must be called when done iterating over list, as it decrements the
+ * refcount of the current node. Necessary in case iteration exited before
+ * the end of the list was reached, and always good form.
+ */
+void klist_iter_exit(struct klist_iter *i)
+{
+	if (i->i_cur) {
+		klist_put(i->i_cur, false);
+		i->i_cur = NULL;
+	}
+}
+EXPORT_SYMBOL_GPL(klist_iter_exit);
+
+static struct klist_node *to_klist_node(struct list_head *n)
+{
+	return container_of(n, struct klist_node, n_node);
+}
+
+/**
+ * klist_prev - Ante up prev node in list.
+ * @i: Iterator structure.
+ *
+ * First grab list lock. Decrement the reference count of the previous
+ * node, if there was one. Grab the prev node, increment its reference
+ * count, drop the lock, and return that prev node.
+ */
+struct klist_node *klist_prev(struct klist_iter *i)
+{
+	void (*put)(struct klist_node *) = i->i_klist->put;
+	struct klist_node *last = i->i_cur;
+	struct klist_node *prev;
+	unsigned long flags;
+
+	spin_lock_irqsave(&i->i_klist->k_lock, flags);
+
+	if (last) {
+		prev = to_klist_node(last->n_node.prev);
+		if (!klist_dec_and_del(last))
+			put = NULL;
+	} else
+		prev = to_klist_node(i->i_klist->k_list.prev);
+
+	i->i_cur = NULL;
+	while (prev != to_klist_node(&i->i_klist->k_list)) {
+		if (likely(!knode_dead(prev))) {
+			kref_get(&prev->n_ref);
+			i->i_cur = prev;
+			break;
+		}
+		prev = to_klist_node(prev->n_node.prev);
+	}
+
+	spin_unlock_irqrestore(&i->i_klist->k_lock, flags);
+
+	if (put && last)
+		put(last);
+	return i->i_cur;
+}
+EXPORT_SYMBOL_GPL(klist_prev);
+
+/**
+ * klist_next - Ante up next node in list.
+ * @i: Iterator structure.
+ *
+ * First grab list lock. Decrement the reference count of the previous
+ * node, if there was one. Grab the next node, increment its reference
+ * count, drop the lock, and return that next node.
+ */
+struct klist_node *klist_next(struct klist_iter *i)
+{
+	void (*put)(struct klist_node *) = i->i_klist->put;
+	struct klist_node *last = i->i_cur;
+	struct klist_node *next;
+	unsigned long flags;
+
+	spin_lock_irqsave(&i->i_klist->k_lock, flags);
+
+	if (last) {
+		next = to_klist_node(last->n_node.next);
+		if (!klist_dec_and_del(last))
+			put = NULL;
+	} else
+		next = to_klist_node(i->i_klist->k_list.next);
+
+	i->i_cur = NULL;
+	while (next != to_klist_node(&i->i_klist->k_list)) {
+		if (likely(!knode_dead(next))) {
+			kref_get(&next->n_ref);
+			i->i_cur = next;
+			break;
+		}
+		next = to_klist_node(next->n_node.next);
+	}
+
+	spin_unlock_irqrestore(&i->i_klist->k_lock, flags);
+
+	if (put && last)
+		put(last);
+	return i->i_cur;
+}
+EXPORT_SYMBOL_GPL(klist_next);