source: vendor/current/lib/util/memcache.c

/*
   Unix SMB/CIFS implementation.
   In-memory cache
   Copyright (C) Volker Lendecke 2007

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

#include "replace.h"
#include <talloc.h>
#include "../lib/util/debug.h"
#include "../lib/util/samba_util.h"
#include "../lib/util/dlinklist.h"
#include "../lib/util/rbtree.h"
#include "memcache.h"

static struct memcache *global_cache;

struct memcache_element {
        struct rb_node rb_node;
        struct memcache_element *prev, *next;
        size_t keylength, valuelength;
        uint8_t n;              /* This is really an enum, but save memory */
        char data[1];           /* placeholder for offsetof */
};

struct memcache {
        struct memcache_element *mru;
        struct rb_root tree;
        size_t size;
        size_t max_size;
};

static void memcache_element_parse(struct memcache_element *e,
                                   DATA_BLOB *key, DATA_BLOB *value);

static bool memcache_is_talloc(enum memcache_number n)
{
        bool result;

        switch (n) {
        case GETPWNAM_CACHE:
        case PDB_GETPWSID_CACHE:
        case SINGLETON_CACHE_TALLOC:
        case SHARE_MODE_LOCK_CACHE:
                result = true;
                break;
        default:
                result = false;
                break;
        }

        return result;
}

static int memcache_destructor(struct memcache *cache) {
        struct memcache_element *e, *next;

        for (e = cache->mru; e != NULL; e = next) {
                next = e->next;
                TALLOC_FREE(e);
        }
        return 0;
}

struct memcache *memcache_init(TALLOC_CTX *mem_ctx, size_t max_size)
{
        struct memcache *result;

        result = talloc_zero(mem_ctx, struct memcache);
        if (result == NULL) {
                return NULL;
        }
        result->max_size = max_size;
        talloc_set_destructor(result, memcache_destructor);
        return result;
}

void memcache_set_global(struct memcache *cache)
{
        TALLOC_FREE(global_cache);
        global_cache = cache;
}

static struct memcache_element *memcache_node2elem(struct rb_node *node)
{
        return (struct memcache_element *)
                ((char *)node - offsetof(struct memcache_element, rb_node));
}

static void memcache_element_parse(struct memcache_element *e,
                                   DATA_BLOB *key, DATA_BLOB *value)
{
        key->data = ((uint8_t *)e) + offsetof(struct memcache_element, data);
        key->length = e->keylength;
        value->data = key->data + e->keylength;
        value->length = e->valuelength;
}

static size_t memcache_element_size(size_t key_length, size_t value_length)
{
        return sizeof(struct memcache_element) - 1 + key_length + value_length;
}

static int memcache_compare(struct memcache_element *e, enum memcache_number n,
                            DATA_BLOB key)
{
        DATA_BLOB this_key, this_value;

        if ((int)e->n < (int)n) return 1;
        if ((int)e->n > (int)n) return -1;

        if (e->keylength < key.length) return 1;
        if (e->keylength > key.length) return -1;

        memcache_element_parse(e, &this_key, &this_value);
        return memcmp(this_key.data, key.data, key.length);
}

static struct memcache_element *memcache_find(
        struct memcache *cache, enum memcache_number n, DATA_BLOB key)
{
        struct rb_node *node;

        node = cache->tree.rb_node;

        while (node != NULL) {
                struct memcache_element *elem = memcache_node2elem(node);
                int cmp;

                cmp = memcache_compare(elem, n, key);
                if (cmp == 0) {
                        return elem;
                }
                node = (cmp < 0) ? node->rb_left : node->rb_right;
        }

        return NULL;
}

bool memcache_lookup(struct memcache *cache, enum memcache_number n,
                     DATA_BLOB key, DATA_BLOB *value)
{
        struct memcache_element *e;

        if (cache == NULL) {
                cache = global_cache;
        }
        if (cache == NULL) {
                return false;
        }

        e = memcache_find(cache, n, key);
        if (e == NULL) {
                return false;
        }

        if (cache->size != 0) {
                DLIST_PROMOTE(cache->mru, e);
        }

        memcache_element_parse(e, &key, value);
        return true;
}

void *memcache_lookup_talloc(struct memcache *cache, enum memcache_number n,
                             DATA_BLOB key)
{
        DATA_BLOB value;
        void *result;

        if (!memcache_lookup(cache, n, key, &value)) {
                return NULL;
        }

        if (value.length != sizeof(result)) {
                return NULL;
        }

        memcpy(&result, value.data, sizeof(result));

        return result;
}

static void memcache_delete_element(struct memcache *cache,
                                    struct memcache_element *e)
{
        rb_erase(&e->rb_node, &cache->tree);

        DLIST_REMOVE(cache->mru, e);

        if (memcache_is_talloc(e->n)) {
                DATA_BLOB cache_key, cache_value;
                void *ptr;

                memcache_element_parse(e, &cache_key, &cache_value);
                SMB_ASSERT(cache_value.length == sizeof(ptr));
                memcpy(&ptr, cache_value.data, sizeof(ptr));
                TALLOC_FREE(ptr);
        }

        cache->size -= memcache_element_size(e->keylength, e->valuelength);

        TALLOC_FREE(e);
}

static void memcache_trim(struct memcache *cache)
{
        if (cache->max_size == 0) {
                return;
        }

        while ((cache->size > cache->max_size) && DLIST_TAIL(cache->mru)) {
                memcache_delete_element(cache, DLIST_TAIL(cache->mru));
        }
}

void memcache_delete(struct memcache *cache, enum memcache_number n,
                     DATA_BLOB key)
{
        struct memcache_element *e;

        if (cache == NULL) {
                cache = global_cache;
        }
        if (cache == NULL) {
                return;
        }

        e = memcache_find(cache, n, key);
        if (e == NULL) {
                return;
        }

        memcache_delete_element(cache, e);
}

void memcache_add(struct memcache *cache, enum memcache_number n,
                  DATA_BLOB key, DATA_BLOB value)
{
        struct memcache_element *e;
        struct rb_node **p;
        struct rb_node *parent;
        DATA_BLOB cache_key, cache_value;
        size_t element_size;

        if (cache == NULL) {
                cache = global_cache;
        }
        if (cache == NULL) {
                return;
        }

        if (key.length == 0) {
                return;
        }

        e = memcache_find(cache, n, key);

        if (e != NULL) {
                memcache_element_parse(e, &cache_key, &cache_value);

                if (value.length <= cache_value.length) {
                        if (memcache_is_talloc(e->n)) {
                                void *ptr;
                                SMB_ASSERT(cache_value.length == sizeof(ptr));
                                memcpy(&ptr, cache_value.data, sizeof(ptr));
                                TALLOC_FREE(ptr);
                        }
                        /*
                         * We can reuse the existing record
                         */
                        memcpy(cache_value.data, value.data, value.length);
                        e->valuelength = value.length;
                        return;
                }

                memcache_delete_element(cache, e);
        }

        element_size = memcache_element_size(key.length, value.length);

        e = talloc_size(cache, element_size);
        if (e == NULL) {
                DEBUG(0, ("talloc failed\n"));
                return;
        }
        talloc_set_type(e, struct memcache_element);

        e->n = n;
        e->keylength = key.length;
        e->valuelength = value.length;

        memcache_element_parse(e, &cache_key, &cache_value);
        memcpy(cache_key.data, key.data, key.length);
        memcpy(cache_value.data, value.data, value.length);

        parent = NULL;
        p = &cache->tree.rb_node;

        while (*p) {
                struct memcache_element *elem = memcache_node2elem(*p);
                int cmp;

                parent = (*p);

                cmp = memcache_compare(elem, n, key);

                p = (cmp < 0) ? &(*p)->rb_left : &(*p)->rb_right;
        }

        rb_link_node(&e->rb_node, parent, p);
        rb_insert_color(&e->rb_node, &cache->tree);

        DLIST_ADD(cache->mru, e);

        cache->size += element_size;
        memcache_trim(cache);
}

void memcache_add_talloc(struct memcache *cache, enum memcache_number n,
                         DATA_BLOB key, void *pptr)
{
        void **ptr = (void **)pptr;
        void *p;

        if (cache == NULL) {
                cache = global_cache;
        }
        if (cache == NULL) {
                return;
        }

        p = talloc_move(cache, ptr);
        memcache_add(cache, n, key, data_blob_const(&p, sizeof(p)));
}

void memcache_flush(struct memcache *cache, enum memcache_number n)
{
        struct rb_node *node;

        if (cache == NULL) {
                cache = global_cache;
        }
        if (cache == NULL) {
                return;
        }

        /*
         * Find the smallest element of number n
         */

        node = cache->tree.rb_node;
        if (node == NULL) {
                return;
        }

        /*
         * First, find *any* element of number n
         */

        while (true) {
                struct memcache_element *elem = memcache_node2elem(node);
                struct rb_node *next;

                if ((int)elem->n == (int)n) {
                        break;
                }

                if ((int)elem->n < (int)n) {
                        next = node->rb_right;
                }
                else {
                        next = node->rb_left;
                }
                if (next == NULL) {
                        break;
                }
                node = next;
        }

        /*
         * Then, find the leftmost element with number n
         */

        while (true) {
                struct rb_node *prev = rb_prev(node);
                struct memcache_element *elem;

                if (prev == NULL) {
                        break;
                }
                elem = memcache_node2elem(prev);
                if ((int)elem->n != (int)n) {
                        break;
                }
                node = prev;
        }

        while (node != NULL) {
                struct memcache_element *e = memcache_node2elem(node);
                struct rb_node *next = rb_next(node);

                if (e->n != n) {
                        break;
                }

                memcache_delete_element(cache, e);
                node = next;
        }
}