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/*
* Copyright (C) 2011 STRATO AG
* written by Arne Jansen <sensille@gmx.net>
* Distributed under the GNU GPL license version 2.
*/
#include <linux/slab.h>
#include <linux/module.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.
*
* The implementation is preliminary and can probably be sped up
* significantly. A first step would be to store the values in an rbtree
* as soon as ULIST_SIZE is exceeded.
*
* 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);
* elem = NULL;
*
* while ((elem = ulist_next(ulist, elem)) {
* 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 adressable 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.
*/
/**
* ulist_init - 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)
{
ulist->nnodes = 0;
ulist->nodes = ulist->int_nodes;
ulist->nodes_alloced = ULIST_SIZE;
}
EXPORT_SYMBOL(ulist_init);
/**
* ulist_fini - 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_fini(struct ulist *ulist)
{
/*
* The first ULIST_SIZE elements are stored inline in struct ulist.
* Only if more elements are alocated they need to be freed.
*/
if (ulist->nodes_alloced > ULIST_SIZE)
kfree(ulist->nodes);
ulist->nodes_alloced = 0; /* in case ulist_fini is called twice */
}
EXPORT_SYMBOL(ulist_fini);
/**
* ulist_reinit - 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)
{
ulist_fini(ulist);
ulist_init(ulist);
}
EXPORT_SYMBOL(ulist_reinit);
/**
* ulist_alloc - 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(unsigned long gfp_mask)
{
struct ulist *ulist = kmalloc(sizeof(*ulist), gfp_mask);
if (!ulist)
return NULL;
ulist_init(ulist);
return ulist;
}
EXPORT_SYMBOL(ulist_alloc);
/**
* ulist_free - free dynamically allocated ulist
* @ulist: ulist to free
*
* It is not necessary to call ulist_fini before.
*/
void ulist_free(struct ulist *ulist)
{
if (!ulist)
return;
ulist_fini(ulist);
kfree(ulist);
}
EXPORT_SYMBOL(ulist_free);
/**
* ulist_add - 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, unsigned long aux,
unsigned long gfp_mask)
{
int i;
for (i = 0; i < ulist->nnodes; ++i) {
if (ulist->nodes[i].val == val)
return 0;
}
if (ulist->nnodes >= ulist->nodes_alloced) {
u64 new_alloced = ulist->nodes_alloced + 128;
struct ulist_node *new_nodes;
void *old = NULL;
/*
* if nodes_alloced == ULIST_SIZE no memory has been allocated
* yet, so pass NULL to krealloc
*/
if (ulist->nodes_alloced > ULIST_SIZE)
old = ulist->nodes;
new_nodes = krealloc(old, sizeof(*new_nodes) * new_alloced,
gfp_mask);
if (!new_nodes)
return -ENOMEM;
if (!old)
memcpy(new_nodes, ulist->int_nodes,
sizeof(ulist->int_nodes));
ulist->nodes = new_nodes;
ulist->nodes_alloced = new_alloced;
}
ulist->nodes[ulist->nnodes].val = val;
ulist->nodes[ulist->nnodes].aux = aux;
++ulist->nnodes;
return 1;
}
EXPORT_SYMBOL(ulist_add);
/**
* ulist_next - iterate ulist
* @ulist: ulist to iterate
* @prev: previously returned element or %NULL to start iteration
*
* 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. The iteration is started with
* @prev = %NULL. 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(struct ulist *ulist, struct ulist_node *prev)
{
int next;
if (ulist->nnodes == 0)
return NULL;
if (!prev)
return &ulist->nodes[0];
next = (prev - ulist->nodes) + 1;
if (next < 0 || next >= ulist->nnodes)
return NULL;
return &ulist->nodes[next];
}
EXPORT_SYMBOL(ulist_next);
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