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+/*
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+ * klist.c - Routines for manipulating klists.
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+ *
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+ *
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+ * This klist interface provides a couple of structures that wrap around
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+ * struct list_head to provide explicit list "head" (struct klist) and
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+ * list "node" (struct klist_node) objects. For struct klist, a spinlock
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+ * is included that protects access to the actual list itself. struct
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+ * klist_node provides a pointer to the klist that owns it and a kref
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+ * reference count that indicates the number of current users of that node
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+ * in the list.
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+ *
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+ * The entire point is to provide an interface for iterating over a list
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+ * that is safe and allows for modification of the list during the
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+ * iteration (e.g. insertion and removal), including modification of the
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+ * current node on the list.
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+ *
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+ * It works using a 3rd object type - struct klist_iter - that is declared
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+ * and initialized before an iteration. klist_next() is used to acquire the
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+ * next element in the list. It returns NULL if there are no more items.
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+ * Internally, that routine takes the klist's lock, decrements the reference
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+ * count of the previous klist_node and increments the count of the next
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+ * klist_node. It then drops the lock and returns.
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+ *
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+ * There are primitives for adding and removing nodes to/from a klist.
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+ * When deleting, klist_del() will simply decrement the reference count.
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+ * Only when the count goes to 0 is the node removed from the list.
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+ * klist_remove() will try to delete the node from the list and block
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+ * until it is actually removed. This is useful for objects (like devices)
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+ * that have been removed from the system and must be freed (but must wait
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+ * until all accessors have finished).
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+ *
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+ * Copyright (C) 2005 Patrick Mochel
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+ *
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+ * This file is released under the GPL v2.
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+ */
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+
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+#include <linux/klist.h>
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+#include <linux/module.h>
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+
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+
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+/**
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+ * klist_init - Initialize a klist structure.
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+ * @k: The klist we're initializing.
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+ */
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+
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+void klist_init(struct klist * k)
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+{
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+ INIT_LIST_HEAD(&k->k_list);
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+ spin_lock_init(&k->k_lock);
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+}
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+
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+EXPORT_SYMBOL_GPL(klist_init);
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+
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+
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+static void add_head(struct klist * k, struct klist_node * n)
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+{
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+ spin_lock(&k->k_lock);
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+ list_add(&n->n_node, &k->k_list);
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+ spin_unlock(&k->k_lock);
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+}
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+
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+static void add_tail(struct klist * k, struct klist_node * n)
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+{
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+ spin_lock(&k->k_lock);
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+ list_add_tail(&n->n_node, &k->k_list);
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+ spin_unlock(&k->k_lock);
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+}
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+
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+
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+static void klist_node_init(struct klist * k, struct klist_node * n)
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+{
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+ INIT_LIST_HEAD(&n->n_node);
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+ init_completion(&n->n_removed);
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+ kref_init(&n->n_ref);
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+ n->n_klist = k;
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+}
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+
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+
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+/**
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+ * klist_add_head - Initialize a klist_node and add it to front.
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+ * @k: klist it's going on.
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+ * @n: node we're adding.
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+ */
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+
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+void klist_add_head(struct klist * k, struct klist_node * n)
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+{
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+ klist_node_init(k, n);
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+ add_head(k, n);
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+}
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+
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+EXPORT_SYMBOL_GPL(klist_add_head);
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+
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+
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+/**
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+ * klist_add_tail - Initialize a klist_node and add it to back.
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+ * @k: klist it's going on.
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+ * @n: node we're adding.
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+ */
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+
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+void klist_add_tail(struct klist * k, struct klist_node * n)
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+{
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+ klist_node_init(k, n);
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+ add_tail(k, n);
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+}
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+
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+EXPORT_SYMBOL_GPL(klist_add_tail);
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+
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+
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+static void klist_release(struct kref * kref)
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+{
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+ struct klist_node * n = container_of(kref, struct klist_node, n_ref);
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+ list_del(&n->n_node);
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+ complete(&n->n_removed);
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+}
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+
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+static int klist_dec_and_del(struct klist_node * n)
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+{
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+ return kref_put(&n->n_ref, klist_release);
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+}
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+
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+
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+/**
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+ * klist_del - Decrement the reference count of node and try to remove.
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+ * @n: node we're deleting.
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+ */
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+
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+void klist_del(struct klist_node * n)
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+{
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+ struct klist * k = n->n_klist;
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+
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+ spin_lock(&k->k_lock);
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+ klist_dec_and_del(n);
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+ spin_unlock(&k->k_lock);
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+}
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+
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+EXPORT_SYMBOL_GPL(klist_del);
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+
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+
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+/**
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+ * klist_remove - Decrement the refcount of node and wait for it to go away.
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+ * @n: node we're removing.
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+ */
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+
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+void klist_remove(struct klist_node * n)
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+{
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+ spin_lock(&n->n_klist->k_lock);
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+ klist_dec_and_del(n);
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+ spin_unlock(&n->n_klist->k_lock);
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+ wait_for_completion(&n->n_removed);
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+}
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+
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+EXPORT_SYMBOL_GPL(klist_remove);
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+
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+
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+/**
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+ * klist_iter_init_node - Initialize a klist_iter structure.
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+ * @k: klist we're iterating.
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+ * @i: klist_iter we're filling.
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+ * @n: node to start with.
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+ *
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+ * Similar to klist_iter_init(), but starts the action off with @n,
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+ * instead of with the list head.
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+ */
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+
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+void klist_iter_init_node(struct klist * k, struct klist_iter * i, struct klist_node * n)
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+{
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+ i->i_klist = k;
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+ i->i_head = &k->k_list;
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+ i->i_cur = n;
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+}
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+
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+EXPORT_SYMBOL_GPL(klist_iter_init_node);
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+
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+
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+/**
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+ * klist_iter_init - Iniitalize a klist_iter structure.
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+ * @k: klist we're iterating.
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+ * @i: klist_iter structure we're filling.
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+ *
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+ * Similar to klist_iter_init_node(), but start with the list head.
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+ */
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+
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+void klist_iter_init(struct klist * k, struct klist_iter * i)
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+{
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+ klist_iter_init_node(k, i, NULL);
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+}
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+
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+EXPORT_SYMBOL_GPL(klist_iter_init);
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+
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+
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+/**
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+ * klist_iter_exit - Finish a list iteration.
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+ * @i: Iterator structure.
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+ *
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+ * Must be called when done iterating over list, as it decrements the
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+ * refcount of the current node. Necessary in case iteration exited before
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+ * the end of the list was reached, and always good form.
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+ */
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+
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+void klist_iter_exit(struct klist_iter * i)
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+{
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+ if (i->i_cur) {
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+ klist_del(i->i_cur);
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+ i->i_cur = NULL;
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+ }
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+}
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+
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+EXPORT_SYMBOL_GPL(klist_iter_exit);
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+
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+
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+static struct klist_node * to_klist_node(struct list_head * n)
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+{
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+ return container_of(n, struct klist_node, n_node);
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+}
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+
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+
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+/**
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+ * klist_next - Ante up next node in list.
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+ * @i: Iterator structure.
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+ *
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+ * First grab list lock. Decrement the reference count of the previous
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+ * node, if there was one. Grab the next node, increment its reference
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+ * count, drop the lock, and return that next node.
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+ */
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+
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+struct klist_node * klist_next(struct klist_iter * i)
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+{
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+ struct list_head * next;
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+ struct klist_node * knode = NULL;
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+
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+ spin_lock(&i->i_klist->k_lock);
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+ if (i->i_cur) {
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+ next = i->i_cur->n_node.next;
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+ klist_dec_and_del(i->i_cur);
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+ } else
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+ next = i->i_head->next;
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+
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+ if (next != i->i_head) {
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+ knode = to_klist_node(next);
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+ kref_get(&knode->n_ref);
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+ }
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+ i->i_cur = knode;
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+ spin_unlock(&i->i_klist->k_lock);
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+ return knode;
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+}
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+
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+EXPORT_SYMBOL_GPL(klist_next);
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mochel@digitalimplant.org