fs/btrfs/ulist.c

   1 /*
   2  * Copyright (C) 2011 STRATO AG
   3  * written by Arne Jansen <sensille@gmx.net>
   4  * Distributed under the GNU GPL license version 2.
   5  */
   6
   7 #include <linux/slab.h>
   8 #include <linux/module.h>
   9 #include "ulist.h"
  10
  11 /*
  12  * ulist is a generic data structure to hold a collection of unique u64
  13  * values. The only operations it supports is adding to the list and
  14  * enumerating it.
  15  * It is possible to store an auxiliary value along with the key.
  16  *
  17  * The implementation is preliminary and can probably be sped up
  18  * significantly. A first step would be to store the values in an rbtree
  19  * as soon as ULIST_SIZE is exceeded.
  20  *
  21  * A sample usage for ulists is the enumeration of directed graphs without
  22  * visiting a node twice. The pseudo-code could look like this:
  23  *
  24  * ulist = ulist_alloc();
  25  * ulist_add(ulist, root);
  26  * elem = NULL;
  27  *
  28  * while ((elem = ulist_next(ulist, elem)) {
  29  *      for (all child nodes n in elem)
  30  *              ulist_add(ulist, n);
  31  *      do something useful with the node;
  32  * }
  33  * ulist_free(ulist);
  34  *
  35  * This assumes the graph nodes are adressable by u64. This stems from the
  36  * usage for tree enumeration in btrfs, where the logical addresses are
  37  * 64 bit.
  38  *
  39  * It is also useful for tree enumeration which could be done elegantly
  40  * recursively, but is not possible due to kernel stack limitations. The
  41  * loop would be similar to the above.
  42  */
  43
  44 /**
  45  * ulist_init - freshly initialize a ulist
  46  * @ulist:      the ulist to initialize
  47  *
  48  * Note: don't use this function to init an already used ulist, use
  49  * ulist_reinit instead.
  50  */
  51 void ulist_init(struct ulist *ulist)
  52 {
  53         ulist->nnodes = 0;
  54         ulist->nodes = ulist->int_nodes;
  55         ulist->nodes_alloced = ULIST_SIZE;
  56 }
  57 EXPORT_SYMBOL(ulist_init);
  58
  59 /**
  60  * ulist_fini - free up additionally allocated memory for the ulist
  61  * @ulist:      the ulist from which to free the additional memory
  62  *
  63  * This is useful in cases where the base 'struct ulist' has been statically
  64  * allocated.
  65  */
  66 void ulist_fini(struct ulist *ulist)
  67 {
  68         /*
  69          * The first ULIST_SIZE elements are stored inline in struct ulist.
  70          * Only if more elements are alocated they need to be freed.
  71          */
  72         if (ulist->nodes_alloced > ULIST_SIZE)
  73                 kfree(ulist->nodes);
  74         ulist->nodes_alloced = 0;       /* in case ulist_fini is called twice */
  75 }
  76 EXPORT_SYMBOL(ulist_fini);
  77
  78 /**
  79  * ulist_reinit - prepare a ulist for reuse
  80  * @ulist:      ulist to be reused
  81  *
  82  * Free up all additional memory allocated for the list elements and reinit
  83  * the ulist.
  84  */
  85 void ulist_reinit(struct ulist *ulist)
  86 {
  87         ulist_fini(ulist);
  88         ulist_init(ulist);
  89 }
  90 EXPORT_SYMBOL(ulist_reinit);
  91
  92 /**
  93  * ulist_alloc - dynamically allocate a ulist
  94  * @gfp_mask:   allocation flags to for base allocation
  95  *
  96  * The allocated ulist will be returned in an initialized state.
  97  */
  98 struct ulist *ulist_alloc(unsigned long gfp_mask)
  99 {
 100         struct ulist *ulist = kmalloc(sizeof(*ulist), gfp_mask);
 101
 102         if (!ulist)
 103                 return NULL;
 104
 105         ulist_init(ulist);
 106
 107         return ulist;
 108 }
 109 EXPORT_SYMBOL(ulist_alloc);
 110
 111 /**
 112  * ulist_free - free dynamically allocated ulist
 113  * @ulist:      ulist to free
 114  *
 115  * It is not necessary to call ulist_fini before.
 116  */
 117 void ulist_free(struct ulist *ulist)
 118 {
 119         if (!ulist)
 120                 return;
 121         ulist_fini(ulist);
 122         kfree(ulist);
 123 }
 124 EXPORT_SYMBOL(ulist_free);
 125
 126 /**
 127  * ulist_add - add an element to the ulist
 128  * @ulist:      ulist to add the element to
 129  * @val:        value to add to ulist
 130  * @aux:        auxiliary value to store along with val
 131  * @gfp_mask:   flags to use for allocation
 132  *
 133  * Note: locking must be provided by the caller. In case of rwlocks write
 134  *       locking is needed
 135  *
 136  * Add an element to a ulist. The @val will only be added if it doesn't
 137  * already exist. If it is added, the auxiliary value @aux is stored along with
 138  * it. In case @val already exists in the ulist, @aux is ignored, even if
 139  * it differs from the already stored value.
 140  *
 141  * ulist_add returns 0 if @val already exists in ulist and 1 if @val has been
 142  * inserted.
 143  * In case of allocation failure -ENOMEM is returned and the ulist stays
 144  * unaltered.
 145  */
 146 int ulist_add(struct ulist *ulist, u64 val, unsigned long aux,
 147               unsigned long gfp_mask)
 148 {
 149         int i;
 150
 151         for (i = 0; i < ulist->nnodes; ++i) {
 152                 if (ulist->nodes[i].val == val)
 153                         return 0;
 154         }
 155
 156         if (ulist->nnodes >= ulist->nodes_alloced) {
 157                 u64 new_alloced = ulist->nodes_alloced + 128;
 158                 struct ulist_node *new_nodes;
 159                 void *old = NULL;
 160
 161                 /*
 162                  * if nodes_alloced == ULIST_SIZE no memory has been allocated
 163                  * yet, so pass NULL to krealloc
 164                  */
 165                 if (ulist->nodes_alloced > ULIST_SIZE)
 166                         old = ulist->nodes;
 167
 168                 new_nodes = krealloc(old, sizeof(*new_nodes) * new_alloced,
 169                                      gfp_mask);
 170                 if (!new_nodes)
 171                         return -ENOMEM;
 172
 173                 if (!old)
 174                         memcpy(new_nodes, ulist->int_nodes,
 175                                sizeof(ulist->int_nodes));
 176
 177                 ulist->nodes = new_nodes;
 178                 ulist->nodes_alloced = new_alloced;
 179         }
 180         ulist->nodes[ulist->nnodes].val = val;
 181         ulist->nodes[ulist->nnodes].aux = aux;
 182         ++ulist->nnodes;
 183
 184         return 1;
 185 }
 186 EXPORT_SYMBOL(ulist_add);
 187
 188 /**
 189  * ulist_next - iterate ulist
 190  * @ulist:      ulist to iterate
 191  * @prev:       previously returned element or %NULL to start iteration
 192  *
 193  * Note: locking must be provided by the caller. In case of rwlocks only read
 194  *       locking is needed
 195  *
 196  * This function is used to iterate an ulist. The iteration is started with
 197  * @prev = %NULL. It returns the next element from the ulist or %NULL when the
 198  * end is reached. No guarantee is made with respect to the order in which
 199  * the elements are returned. They might neither be returned in order of
 200  * addition nor in ascending order.
 201  * It is allowed to call ulist_add during an enumeration. Newly added items
 202  * are guaranteed to show up in the running enumeration.
 203  */
 204 struct ulist_node *ulist_next(struct ulist *ulist, struct ulist_node *prev)
 205 {
 206         int next;
 207
 208         if (ulist->nnodes == 0)
 209                 return NULL;
 210
 211         if (!prev)
 212                 return &ulist->nodes[0];
 213
 214         next = (prev - ulist->nodes) + 1;
 215         if (next < 0 || next >= ulist->nnodes)
 216                 return NULL;
 217
 218         return &ulist->nodes[next];
 219 }
 220 EXPORT_SYMBOL(ulist_next);