cache_mngt.c

/*
 * lib/cache_mngt.c     Cache Management
 *
 *      This library is free software; you can redistribute it and/or
 *      modify it under the terms of the GNU Lesser General Public
 *      License as published by the Free Software Foundation version 2.1
 *      of the License.
 *
 * Copyright (c) 2003-2012 Thomas Graf <tgraf@suug.ch>
 */

/**
 * @ingroup core
 * @defgroup cache_mngt Caching System
 *
 * Related sections in the development guide:
 * - @core_doc{core_cache, Caching System}
 *
 * @{
 *
 * Header
 * ------
 * ~~~~{.c}
 * #include <netlink/cache.h>
 * ~~~~
 */

#include <netlink-private/netlink.h>
#include <netlink/netlink.h>
#include <netlink/cache.h>
#include <netlink/utils.h>

static struct nl_cache_ops *cache_ops;
static NL_RW_LOCK(cache_ops_lock);

/**
 * @name Cache Operations Sets
 * @{
 */

struct nl_cache_ops *__nl_cache_ops_lookup(const char *name)
{
        struct nl_cache_ops *ops;

        for (ops = cache_ops; ops; ops = ops->co_next)
                if (!strcmp(ops->co_name, name))
                        return ops;

        return NULL;
}

/**
 * Increment reference counter
 * @arg ops             Cache operations
 */
void nl_cache_ops_get(struct nl_cache_ops *ops)
{
        ops->co_refcnt++;
}

/**
 * Decrement reference counter
 * @arg ops             Cache operations
 */
void nl_cache_ops_put(struct nl_cache_ops *ops)
{
        ops->co_refcnt--;
}

/**
 * Lookup cache operations by name
 * @arg name            name of the cache type
 *
 * @attention This function is not safe, it does not increment the reference
 *            counter. Please use nl_cache_ops_lookup_safe().
 *
 * @return The cache operations or NULL if not found.
 */
struct nl_cache_ops *nl_cache_ops_lookup(const char *name)
{
        struct nl_cache_ops *ops;

        nl_read_lock(&cache_ops_lock);
        ops = __nl_cache_ops_lookup(name);
        nl_read_unlock(&cache_ops_lock);

        return ops;
}

/**
 * Lookup cache operations by name
 * @arg name            name of the cache type
 *
 * @note The reference counter of the returned cache operation is incremented
 *       and must be decremented after use with nl_cache_ops_put().
 *
 * @return The cache operations or NULL if not found.
 */
struct nl_cache_ops *nl_cache_ops_lookup_safe(const char *name)
{
        struct nl_cache_ops *ops;

        nl_write_lock(&cache_ops_lock);
        if ((ops = __nl_cache_ops_lookup(name)))
                nl_cache_ops_get(ops);
        nl_write_unlock(&cache_ops_lock);

        return ops;
}

static struct nl_cache_ops *__cache_ops_associate(int protocol, int msgtype)
{
        int i;
        struct nl_cache_ops *ops;

        for (ops = cache_ops; ops; ops = ops->co_next) {
                if (ops->co_protocol != protocol)
                        continue;

                for (i = 0; ops->co_msgtypes[i].mt_id >= 0; i++)
                        if (ops->co_msgtypes[i].mt_id == msgtype)
                                return ops;
        }

        return NULL;
}

/**
 * Associate protocol and message type to cache operations
 * @arg protocol                netlink protocol
 * @arg msgtype                 netlink message type
 *
 * @attention This function is not safe, it does not increment the reference
 *            counter. Please use nl_cache_ops_associate_safe().
 *
 * @see nl_cache_ops_associate_safe()
 *
 * @return The cache operations or NULL if no match found.
 */
struct nl_cache_ops *nl_cache_ops_associate(int protocol, int msgtype)
{
        struct nl_cache_ops *ops;

        nl_read_lock(&cache_ops_lock);
        ops = __cache_ops_associate(protocol, msgtype);
        nl_read_unlock(&cache_ops_lock);

        return ops;
}

/**
 * Associate protocol and message type to cache operations
 * @arg protocol                netlink protocol
 * @arg msgtype                 netlink message type
 *
 * Searches the registered cache operations for a matching protocol
 * and message type.
 *
 * @note The reference counter of the returned cache operation is incremented
 *       and must be decremented after use with nl_cache_ops_put().
 *
 * @return The cache operations or NULL if no no match was found.
 */
struct nl_cache_ops *nl_cache_ops_associate_safe(int protocol, int msgtype)
{
        struct nl_cache_ops *ops;

        nl_write_lock(&cache_ops_lock);
        if ((ops = __cache_ops_associate(protocol, msgtype)))
                nl_cache_ops_get(ops);
        nl_write_unlock(&cache_ops_lock);

        return ops;
}

/**
 * Lookup message type cache association
 * @arg ops                     cache operations
 * @arg msgtype                 netlink message type
 *
 * Searches for a matching message type association ing the specified
 * cache operations.
 *
 * @attention The guranteed lifetime of the returned message type is bound
 *            to the lifetime of the underlying cache operations.
 *
 * @return A message type association or NULL.
 */
struct nl_msgtype *nl_msgtype_lookup(struct nl_cache_ops *ops, int msgtype)
{
        int i;

        for (i = 0; ops->co_msgtypes[i].mt_id >= 0; i++)
                if (ops->co_msgtypes[i].mt_id == msgtype)
                        return &ops->co_msgtypes[i];

        return NULL;
}

/* Must hold cache_ops_lock */
static struct nl_cache_ops *cache_ops_lookup_for_obj(struct nl_object_ops *obj_ops)
{
        struct nl_cache_ops *ops;

        for (ops = cache_ops; ops; ops = ops->co_next)
                if (ops->co_obj_ops == obj_ops)
                        return ops;

        return NULL;

}

/**
 * Call a function for each registered cache operation
 * @arg cb              Callback function to be called
 * @arg arg             User specific argument.
 */
void nl_cache_ops_foreach(void (*cb)(struct nl_cache_ops *, void *), void *arg)
{
        struct nl_cache_ops *ops;

        nl_read_lock(&cache_ops_lock);
        for (ops = cache_ops; ops; ops = ops->co_next)
                cb(ops, arg);
        nl_read_unlock(&cache_ops_lock);
}

/**
 * Set default flags for caches of this type
 * @arg ops             Cache ops
 * @arg flags           Flags to set
 *
 * The cache operation flags will be derived to all caches allocates
 * based on this set of cache operations.
 */
void nl_cache_ops_set_flags(struct nl_cache_ops *ops, unsigned int flags)
{
        nl_write_lock(&cache_ops_lock);
        ops->co_flags |= flags;
        nl_write_unlock(&cache_ops_lock);
}

/**
 * Register a set of cache operations
 * @arg ops             cache operations
 *
 * Called by users of caches to announce the avaibility of
 * a certain cache type.
 *
 * @return 0 on success or a negative error code.
 */
int nl_cache_mngt_register(struct nl_cache_ops *ops)
{
        if (!ops->co_name || !ops->co_obj_ops)
                return -NLE_INVAL;

        nl_write_lock(&cache_ops_lock);
        if (__nl_cache_ops_lookup(ops->co_name)) {
                nl_write_unlock(&cache_ops_lock);
                return -NLE_EXIST;
        }

        ops->co_refcnt = 0;
        ops->co_next = cache_ops;
        cache_ops = ops;
        nl_write_unlock(&cache_ops_lock);

        NL_DBG(1, "Registered cache operations %s\n", ops->co_name);

        return 0;
}

/**
 * Unregister a set of cache operations
 * @arg ops             cache operations
 *
 * Called by users of caches to announce a set of
 * cache operations is no longer available. The
 * specified cache operations must have been registered
 * previously using nl_cache_mngt_register()
 *
 * @return 0 on success or a negative error code
 */
int nl_cache_mngt_unregister(struct nl_cache_ops *ops)
{
        struct nl_cache_ops *t, **tp;
        int err = 0;

        nl_write_lock(&cache_ops_lock);

        if (ops->co_refcnt > 0) {
                err = -NLE_BUSY;
                goto errout;
        }

        for (tp = &cache_ops; (t=*tp) != NULL; tp = &t->co_next)
                if (t == ops)
                        break;

        if (!t) {
                err = -NLE_NOCACHE;
                goto errout;
        }

        NL_DBG(1, "Unregistered cache operations %s\n", ops->co_name);

        *tp = t->co_next;
errout:
        nl_write_unlock(&cache_ops_lock);

        return err;
}

/** @} */

/**
 * @name Global Cache Provisioning/Requiring
 * @{
 */

/**
 * Provide a cache for global use
 * @arg cache           cache to provide
 *
 * Offers the specified cache to be used by other modules.
 * Only one cache per type may be shared at a time,
 * a previsouly provided caches will be overwritten.
 */
void nl_cache_mngt_provide(struct nl_cache *cache)
{
        struct nl_cache_ops *ops;

        nl_write_lock(&cache_ops_lock);

        ops = cache_ops_lookup_for_obj(cache->c_ops->co_obj_ops);
        if (!ops)
                BUG();
        else {
                nl_cache_get(cache);

                /*
                 * Hold a reference to the cache operations to ensure the
                 * ops don't go away while we use it to store the cache pointer.
                 */
                if (!ops->co_major_cache)
                        nl_cache_ops_get(ops);

                ops->co_major_cache = cache;
        }

        nl_write_unlock(&cache_ops_lock);
}

/**
 * Unprovide a cache for global use
 * @arg cache           cache to unprovide
 *
 * Cancels the offer to use a cache globally. The
 * cache will no longer be returned via lookups but
 * may still be in use.
 */
void nl_cache_mngt_unprovide(struct nl_cache *cache)
{
        struct nl_cache_ops *ops;

        nl_write_lock(&cache_ops_lock);

        ops = cache_ops_lookup_for_obj(cache->c_ops->co_obj_ops);
        if (!ops)
                BUG();
        else if (ops->co_major_cache == cache) {
                nl_cache_free(ops->co_major_cache);
                nl_cache_ops_put(ops);
                ops->co_major_cache = NULL;
        }

        nl_write_unlock(&cache_ops_lock);
}

struct nl_cache *__nl_cache_mngt_require(const char *name)
{
        struct nl_cache_ops *ops;
        struct nl_cache *cache = NULL;

        ops = nl_cache_ops_lookup_safe(name);
        if (ops) {
                cache = ops->co_major_cache;
                nl_cache_ops_put(ops);
        }
        
        return cache;
}

/**
 * Return cache previously provided via nl_cache_mngt_provide()
 * @arg name            Name of cache to lookup
 *
 * @attention This function is not safe, it does not increment the reference
 *            counter. Please use nl_cache_mngt_require_safe().
 *
 * @see nl_cache_mngt_require_safe()
 *
 * @return Pointer to cache or NULL if none registered
 */
struct nl_cache *nl_cache_mngt_require(const char *name)
{
        struct nl_cache *cache;

        if (!(cache = __nl_cache_mngt_require(name)))
                NL_DBG(1, "Application BUG: Your application must "
                       "call nl_cache_mngt_provide() and\nprovide a valid "
                       "%s cache to be used for internal lookups.\nSee the "
                       " API documentation for more details.\n", name);
        
        return cache;
}

/**
 * Return cache previously provided via nl_cache_mngt_provide()
 * @arg name            Name of cache to lookup
 *
 * @note The reference counter of the returned cache is incremented
 *       and must be decremented after use with nl_cache_put().
 *
 * @return Pointer to cache or NULL if none registered
 */
struct nl_cache *nl_cache_mngt_require_safe(const char *name)
{
        struct nl_cache *cache;

        if ((cache = nl_cache_mngt_require(name)))
                nl_cache_get(cache);
        
        return cache;
}

/** @} */

/** @} */