linux/fs/btrfs/ulist.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2011 STRATO AG
 * written by Arne Jansen <[email protected]>
 */

#include <linux/slab.h>
#include "messages.h"
#include "ulist.h"

/*
 * ulist is a generic data structure to hold a collection of unique u64
 * values. The only operations it supports is adding to the list and
 * enumerating it.
 * It is possible to store an auxiliary value along with the key.
 *
 * A sample usage for ulists is the enumeration of directed graphs without
 * visiting a node twice. The pseudo-code could look like this:
 *
 * ulist = ulist_alloc();
 * ulist_add(ulist, root);
 * ULIST_ITER_INIT(&uiter);
 *
 * while ((elem = ulist_next(ulist, &uiter)) {
 * 	for (all child nodes n in elem)
 *		ulist_add(ulist, n);
 *	do something useful with the node;
 * }
 * ulist_free(ulist);
 *
 * This assumes the graph nodes are addressable by u64. This stems from the
 * usage for tree enumeration in btrfs, where the logical addresses are
 * 64 bit.
 *
 * It is also useful for tree enumeration which could be done elegantly
 * recursively, but is not possible due to kernel stack limitations. The
 * loop would be similar to the above.
 */

/*
 * Freshly initialize a ulist.
 *
 * @ulist:	the ulist to initialize
 *
 * Note: don't use this function to init an already used ulist, use
 * ulist_reinit instead.
 */
void ulist_init(struct ulist *ulist)
{ … }

/*
 * Free up additionally allocated memory for the ulist.
 *
 * @ulist:	the ulist from which to free the additional memory
 *
 * This is useful in cases where the base 'struct ulist' has been statically
 * allocated.
 */
void ulist_release(struct ulist *ulist)
{ … }

/*
 * Prepare a ulist for reuse.
 *
 * @ulist:	ulist to be reused
 *
 * Free up all additional memory allocated for the list elements and reinit
 * the ulist.
 */
void ulist_reinit(struct ulist *ulist)
{ … }

/*
 * Dynamically allocate a ulist.
 *
 * @gfp_mask:	allocation flags to for base allocation
 *
 * The allocated ulist will be returned in an initialized state.
 */
struct ulist *ulist_alloc(gfp_t gfp_mask)
{ … }

void ulist_prealloc(struct ulist *ulist, gfp_t gfp_mask)
{ … }

/*
 * Free dynamically allocated ulist.
 *
 * @ulist:	ulist to free
 *
 * It is not necessary to call ulist_release before.
 */
void ulist_free(struct ulist *ulist)
{ … }

static struct ulist_node *ulist_rbtree_search(struct ulist *ulist, u64 val)
{ … }

static void ulist_rbtree_erase(struct ulist *ulist, struct ulist_node *node)
{ … }

static int ulist_rbtree_insert(struct ulist *ulist, struct ulist_node *ins)
{ … }

/*
 * Add an element to the ulist.
 *
 * @ulist:	ulist to add the element to
 * @val:	value to add to ulist
 * @aux:	auxiliary value to store along with val
 * @gfp_mask:	flags to use for allocation
 *
 * Note: locking must be provided by the caller. In case of rwlocks write
 *       locking is needed
 *
 * Add an element to a ulist. The @val will only be added if it doesn't
 * already exist. If it is added, the auxiliary value @aux is stored along with
 * it. In case @val already exists in the ulist, @aux is ignored, even if
 * it differs from the already stored value.
 *
 * ulist_add returns 0 if @val already exists in ulist and 1 if @val has been
 * inserted.
 * In case of allocation failure -ENOMEM is returned and the ulist stays
 * unaltered.
 */
int ulist_add(struct ulist *ulist, u64 val, u64 aux, gfp_t gfp_mask)
{ … }

int ulist_add_merge(struct ulist *ulist, u64 val, u64 aux,
		    u64 *old_aux, gfp_t gfp_mask)
{ … }

/*
 * Delete one node from ulist.
 *
 * @ulist:	ulist to remove node from
 * @val:	value to delete
 * @aux:	aux to delete
 *
 * The deletion will only be done when *BOTH* val and aux matches.
 * Return 0 for successful delete.
 * Return > 0 for not found.
 */
int ulist_del(struct ulist *ulist, u64 val, u64 aux)
{ … }

/*
 * Iterate ulist.
 *
 * @ulist:	ulist to iterate
 * @uiter:	iterator variable, initialized with ULIST_ITER_INIT(&iterator)
 *
 * Note: locking must be provided by the caller. In case of rwlocks only read
 *       locking is needed
 *
 * This function is used to iterate an ulist.
 * It returns the next element from the ulist or %NULL when the
 * end is reached. No guarantee is made with respect to the order in which
 * the elements are returned. They might neither be returned in order of
 * addition nor in ascending order.
 * It is allowed to call ulist_add during an enumeration. Newly added items
 * are guaranteed to show up in the running enumeration.
 */
struct ulist_node *ulist_next(const struct ulist *ulist, struct ulist_iterator *uiter)
{ … }