[PATCH] Add initial implementation of klist helpers.

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.
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).

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).

Signed-off-by: Patrick Mochel <mochel@digitalimplant.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff -Nru a/include/linux/klist.h b/include/linux/klist.h

1 files changed, 53 insertions, 0 deletions

diff --git a/include/linux/klist.h b/include/linux/klist.h
new file mode 100644
index 000000000000..fb52f9d9d611
--- /dev/null
+++ b/include/linux/klist.h
@@ -0,0 +1,53 @@
+/*
+ *      klist.h - Some generic list helpers, extending struct list_head a bit.
+ *
+ *      Implementations are found in lib/klist.c
+ *
+ *
+ *      Copyright (C) 2005 Patrick Mochel
+ *
+ *      This file is rleased under the GPL v2.
+ */
+
+#include <linux/spinlock.h>
+#include <linux/completion.h>
+#include <linux/kref.h>
+#include <linux/list.h>
+
+
+struct klist {
+        spinlock_t              k_lock;
+        struct list_head        k_list;
+};
+
+
+extern void klist_init(struct klist * k);
+
+
+struct klist_node {
+        struct klist            * n_klist;
+        struct list_head        n_node;
+        struct kref             n_ref;
+        struct completion       n_removed;
+};
+
+extern void klist_add_tail(struct klist * k, struct klist_node * n);
+extern void klist_add_head(struct klist * k, struct klist_node * n);
+
+extern void klist_del(struct klist_node * n);
+extern void klist_remove(struct klist_node * n);
+
+
+struct klist_iter {
+        struct klist            * i_klist;
+        struct list_head        * i_head;
+        struct klist_node       * i_cur;
+};
+
+
+extern void klist_iter_init(struct klist * k, struct klist_iter * i);
+extern void klist_iter_init_node(struct klist * k, struct klist_iter * i, 
+                                 struct klist_node * n);
+extern void klist_iter_exit(struct klist_iter * i);
+extern struct klist_node * klist_next(struct klist_iter * i);
+