datapath: Avoid duplicate test in tnl_free_linked_skbs().

[openvswitch] / datapath / table.c

/*
 * Copyright (c) 2009, 2010, 2011 Nicira Networks.
 * Distributed under the terms of the GNU GPL version 2.
 *
 * Significant portions of this file may be copied from parts of the Linux
 * kernel, by Linus Torvalds and others.
 */

#include "flow.h"
#include "datapath.h"
#include "table.h"

#include <linux/genetlink.h>
#include <linux/gfp.h>
#include <linux/slab.h>
#include <linux/mm.h>
#include <asm/pgtable.h>

/**
 * struct tbl_bucket - single bucket within a hash table
 * @rcu: RCU callback structure
 * @n_objs: number of objects in @objs[] array
 * @objs: array of @n_objs pointers to table nodes contained inside objects
 *
 * The expected number of objects per bucket is 1, but this allows for an
 * arbitrary number of collisions.
 */
struct tbl_bucket {
        struct rcu_head rcu;
        unsigned int n_objs;
        struct tbl_node *objs[];
};

static struct tbl_bucket *get_bucket(struct tbl_bucket __rcu *bucket)
{
        return rcu_dereference_check(bucket, rcu_read_lock_held() ||
                                     lockdep_genl_is_held());
}

static struct tbl_bucket *get_bucket_protected(struct tbl_bucket __rcu *bucket)
{
        return rcu_dereference_protected(bucket, lockdep_genl_is_held());
}

static inline int bucket_size(int n_objs)
{
        return sizeof(struct tbl_bucket) + sizeof(struct tbl_node *) * n_objs;
}

static struct tbl_bucket *bucket_alloc(int n_objs)
{
        return kmalloc(bucket_size(n_objs), GFP_KERNEL);
}

static void free_buckets(struct tbl_bucket __rcu ***l1,
                         unsigned int n_buckets,
                         void (*free_obj)(struct tbl_node *))
{
        unsigned int i;

        for (i = 0; i < n_buckets >> TBL_L1_SHIFT; i++) {
                struct tbl_bucket __rcu **l2 = l1[i];
                unsigned int j;

                for (j = 0; j < TBL_L2_SIZE; j++) {
                        struct tbl_bucket *bucket = (struct tbl_bucket __force *)l2[j];
                        if (!bucket)
                                continue;

                        if (free_obj) {
                                unsigned int k;
                                for (k = 0; k < bucket->n_objs; k++)
                                        free_obj(bucket->objs[k]);
                        }
                        kfree(bucket);
                }
                free_page((unsigned long)l2);
        }
        kfree(l1);
}

static struct tbl_bucket __rcu ***alloc_buckets(unsigned int n_buckets)
{
        struct tbl_bucket __rcu ***l1;
        unsigned int i;

        l1 = kmalloc((n_buckets >> TBL_L1_SHIFT) * sizeof(struct tbl_bucket **),
                     GFP_KERNEL);
        if (!l1)
                return NULL;
        for (i = 0; i < n_buckets >> TBL_L1_SHIFT; i++) {
                l1[i] = (struct tbl_bucket __rcu **)get_zeroed_page(GFP_KERNEL);
                if (!l1[i]) {
                        free_buckets(l1, i << TBL_L1_SHIFT, NULL);
                        return NULL;
                }
        }
        return l1;
}

/**
 * tbl_create - create and return a new hash table
 * @n_buckets: number of buckets in the new table
 *
 * Creates and returns a new hash table, or %NULL if memory cannot be
 * allocated.  @n_buckets must be a power of 2 in the range %TBL_MIN_BUCKETS to
 * %TBL_MAX_BUCKETS.
 */
struct tbl *tbl_create(unsigned int n_buckets)
{
        struct tbl *table;

        table = kzalloc(sizeof(*table), GFP_KERNEL);
        if (!table)
                goto err;

        table->n_buckets = n_buckets;
        table->buckets = alloc_buckets(n_buckets);
        if (!table->buckets)
                goto err_free_table;

        return table;

err_free_table:
        kfree(table);
err:
        return NULL;
}

/**
 * tbl_destroy - destroy hash table and optionally the objects it contains
 * @table: table to destroy
 * @destructor: function to be called on objects at destruction time
 *
 * If a destructor is null, then the buckets in @table are destroyed
 * but not the objects within those buckets.  This behavior is useful when a
 * table is being replaced by a larger or smaller one without destroying the
 * objects.
 *
 * If a destructor is not null, then it is called on the objects in @table
 * before destroying the buckets.
 */
void tbl_destroy(struct tbl *table, void (*destructor)(struct tbl_node *))
{
        if (!table)
                return;

        free_buckets(table->buckets, table->n_buckets, destructor);
        kfree(table);
}

static void destroy_table_rcu(struct rcu_head *rcu)
{
        struct tbl *table = container_of(rcu, struct tbl, rcu);
        tbl_destroy(table, table->obj_destructor);
}

/**
 * tbl_deferred_destroy - destroy table after a RCU grace period
 * @table: table to destroy
 * @destructor: function to be called on objects at destruction time
 *
 * Calls tbl_destroy() on @table after an RCU grace period. If @destructor is
 * not null it is called on every element before the table is destroyed. */
void tbl_deferred_destroy(struct tbl *table, void (*destructor)(struct tbl_node *))
{
        if (!table)
                return;

        table->obj_destructor = destructor;
        call_rcu(&table->rcu, destroy_table_rcu);
}

static struct tbl_bucket __rcu **find_bucket(struct tbl *table, u32 hash)
{
        unsigned int l1 = (hash & (table->n_buckets - 1)) >> TBL_L1_SHIFT;
        unsigned int l2 = hash & ((1 << TBL_L2_BITS) - 1);
        return &table->buckets[l1][l2];
}

static int search_bucket(const struct tbl_bucket *bucket, void *target, u32 hash,
                         int (*cmp)(const struct tbl_node *, void *))
{
        int i;

        for (i = 0; i < bucket->n_objs; i++) {
                struct tbl_node *obj = bucket->objs[i];
                if (obj->hash == hash && likely(cmp(obj, target)))
                        return i;
        }

        return -1;
}

/**
 * tbl_lookup - searches hash table for a matching object
 * @table: hash table to search
 * @target: identifier for the object that is being searched for, will be
 * provided as an argument to @cmp when making comparisions
 * @hash: hash of @target
 * @cmp: comparision function to match objects with the given hash, returns
 * nonzero if the objects match, zero otherwise
 *
 * Searches @table for an object identified by @target.  Returns the tbl_node
 * contained in the object if successful, otherwise %NULL.
 */
struct tbl_node *tbl_lookup(struct tbl *table, void *target, u32 hash,
                            int (*cmp)(const struct tbl_node *, void *))
{
        struct tbl_bucket __rcu **bucketp = find_bucket(table, hash);
        struct tbl_bucket *bucket = get_bucket(*bucketp);
        int index;

        if (!bucket)
                return NULL;

        index = search_bucket(bucket, target, hash, cmp);
        if (index < 0)
                return NULL;

        return bucket->objs[index];
}

/**
 * tbl_foreach - iterate through hash table
 * @table: table to iterate
 * @callback: function to call for each entry
 * @aux: Extra data to pass to @callback
 *
 * Iterates through all of the objects in @table in hash order, passing each of
 * them in turn to @callback.  If @callback returns nonzero, this terminates
 * the iteration and tbl_foreach() returns the same value.  Returns 0 if
 * @callback never returns nonzero.
 *
 * This function does not try to intelligently handle the case where @callback
 * adds or removes flows in @table.
 */
int tbl_foreach(struct tbl *table,
                int (*callback)(struct tbl_node *, void *aux), void *aux)
{
        unsigned int n_l1 = table->n_buckets >> TBL_L1_SHIFT;
        unsigned int l1_idx;

        for (l1_idx = 0; l1_idx < n_l1; l1_idx++) {
                struct tbl_bucket __rcu **l2 = table->buckets[l1_idx];
                unsigned int l2_idx;

                for (l2_idx = 0; l2_idx < TBL_L2_SIZE; l2_idx++) {
                        struct tbl_bucket *bucket;
                        unsigned int i;

                        bucket = get_bucket(l2[l2_idx]);
                        if (!bucket)
                                continue;

                        for (i = 0; i < bucket->n_objs; i++) {
                                int error = (*callback)(bucket->objs[i], aux);
                                if (error)
                                        return error;
                        }
                }
        }
        return 0;
}

/**
 * tbl_next - find next node in hash table
 * @table: table to iterate
 * @bucketp: On entry, hash value of bucket to start from.  On exit, updated
 * to bucket to start from on next call.
 * @objp: On entry, index to start from within first bucket.  On exit, updated
 * to index to start from on next call.
 *
 * Returns the next node in @table in hash order, or %NULL when no nodes remain
 * in the hash table.
 *
 * On entry, uses the values that @bucketp and @objp reference to determine
 * where to begin iteration.  Use 0 for both values to begin a new iteration.
 * On exit, stores the values to pass on the next iteration into @bucketp and
 * @objp's referents.
 */
struct tbl_node *tbl_next(struct tbl *table, u32 *bucketp, u32 *objp)
{
        unsigned int n_l1 = table->n_buckets >> TBL_L1_SHIFT;
        u32 s_l1_idx = *bucketp >> TBL_L1_SHIFT;
        u32 s_l2_idx = *bucketp & (TBL_L2_SIZE - 1);
        u32 s_obj = *objp;
        unsigned int l1_idx;

        for (l1_idx = s_l1_idx; l1_idx < n_l1; l1_idx++) {
                struct tbl_bucket __rcu **l2 = table->buckets[l1_idx];
                unsigned int l2_idx;

                for (l2_idx = s_l2_idx; l2_idx < TBL_L2_SIZE; l2_idx++) {
                        struct tbl_bucket *bucket;

                        bucket = get_bucket_protected(l2[l2_idx]);
                        if (bucket && s_obj < bucket->n_objs) {
                                *bucketp = (l1_idx << TBL_L1_SHIFT) + l2_idx;
                                *objp = s_obj + 1;
                                return bucket->objs[s_obj];
                        }

                        s_obj = 0;
                }
                s_l2_idx = 0;
        }
        *bucketp = 0;
        *objp = 0;
        return NULL;
}

static int insert_table_flow(struct tbl_node *node, void *new_table_)
{
        struct tbl *new_table = new_table_;
        return tbl_insert(new_table, node, node->hash);
}

/**
 * tbl_expand - create a hash table with more buckets
 * @table: table to expand
 *
 * Creates a new table containing the same objects as @table but with twice
 * as many buckets.  Returns 0 if successful, otherwise a negative error.  The
 * caller should free @table upon success (probably using
 * tbl_deferred_destroy()).
 */
struct tbl *tbl_expand(struct tbl *table)
{
        int err;
        int n_buckets = table->n_buckets * 2;
        struct tbl *new_table;

        if (n_buckets >= TBL_MAX_BUCKETS) {
                err = -ENOSPC;
                goto error;
        }

        err = -ENOMEM;
        new_table = tbl_create(TBL_MIN_BUCKETS);
        if (!new_table)
                goto error;

        if (tbl_foreach(table, insert_table_flow, new_table))
                goto error_free_new_table;

        return new_table;

error_free_new_table:
        tbl_destroy(new_table, NULL);
error:
        return ERR_PTR(err);
}

/**
 * tbl_n_buckets - returns the number of buckets
 * @table: table to examine
 *
 * Returns the number of buckets currently allocated in @table, useful when
 * deciding whether to expand.
 */
int tbl_n_buckets(struct tbl *table)
{
        return table->n_buckets;
}

static void free_bucket_rcu(struct rcu_head *rcu)
{
        struct tbl_bucket *bucket = container_of(rcu, struct tbl_bucket, rcu);
        kfree(bucket);
}

/**
 * tbl_insert - insert object into table
 * @table: table in which to insert object
 * @target: tbl_node contained in object to insert
 * @hash: hash of object to insert
 *
 * The caller must ensure that no object considered to be identical to @target
 * already exists in @table.  Returns 0 or a negative error (currently just
 * -ENOMEM).
 */
int tbl_insert(struct tbl *table, struct tbl_node *target, u32 hash)
{
        struct tbl_bucket __rcu **oldp = find_bucket(table, hash);
        struct tbl_bucket *old = get_bucket_protected(*oldp);
        unsigned int n = old ? old->n_objs : 0;
        struct tbl_bucket *new = bucket_alloc(n + 1);

        if (!new)
                return -ENOMEM;

        target->hash = hash;

        new->n_objs = n + 1;
        if (old)
                memcpy(new->objs, old->objs, n * sizeof(struct tbl_node *));
        new->objs[n] = target;

        rcu_assign_pointer(*oldp, new);
        if (old)
                call_rcu(&old->rcu, free_bucket_rcu);

        table->count++;

        return 0;
}

/**
 * tbl_remove - remove object from table
 * @table: table from which to remove object
 * @target: tbl_node inside of object to remove
 *
 * The caller must ensure that @target itself is in @table.  (It is not
 * good enough for @table to contain a different object considered identical
 * @target.)
 *
 * Returns 0 or a negative error (currently just -ENOMEM).  Yes, it *is*
 * possible for object deletion to fail due to lack of memory.
 */
int tbl_remove(struct tbl *table, struct tbl_node *target)
{
        struct tbl_bucket __rcu **oldp = find_bucket(table, target->hash);
        struct tbl_bucket *old = get_bucket_protected(*oldp);
        unsigned int n = old->n_objs;
        struct tbl_bucket *new;

        if (n > 1) {
                unsigned int i;

                new = bucket_alloc(n - 1);
                if (!new)
                        return -ENOMEM;

                new->n_objs = 0;
                for (i = 0; i < n; i++) {
                        struct tbl_node *obj = old->objs[i];
                        if (obj != target)
                                new->objs[new->n_objs++] = obj;
                }
                WARN_ON_ONCE(new->n_objs != n - 1);
        } else {
                new = NULL;
        }

        rcu_assign_pointer(*oldp, new);
        call_rcu(&old->rcu, free_bucket_rcu);

        table->count--;

        return 0;
}

/**
 * tbl_count - retrieves the number of stored objects
 * @table: table to count
 *
 * Returns the number of objects that have been inserted into the hash table.
 */
unsigned int tbl_count(struct tbl *table)
{
        return table->count;
}