libbpf: add resizable non-thread safe internal hashmap

There is a need for fast point lookups inside libbpf for multiple use
cases (e.g., name resolution for BTF-to-C conversion, by-name lookups in
BTF for upcoming BPF CO-RE relocation support, etc). This patch
implements simple resizable non-thread safe hashmap using single linked
list chains.

Four different insert strategies are supported:
 - HASHMAP_ADD - only add key/value if key doesn't exist yet;
 - HASHMAP_SET - add key/value pair if key doesn't exist yet; otherwise,
   update value;
 - HASHMAP_UPDATE - update value, if key already exists; otherwise, do
   nothing and return -ENOENT;
 - HASHMAP_APPEND - always add key/value pair, even if key already exists.
   This turns hashmap into a multimap by allowing multiple values to be
   associated with the same key. Most useful read API for such hashmap is
   hashmap__for_each_key_entry() iteration. If hashmap__find() is still
   used, it will return last inserted key/value entry (first in a bucket
   chain).

For HASHMAP_SET and HASHMAP_UPDATE, old key/value pair is returned, so
that calling code can handle proper memory management, if necessary.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/tools/lib/bpf/Build b/tools/lib/bpf/Build
index ee9d536..dcf0d36 100644 (file)
--- a/tools/lib/bpf/Build
+++ b/tools/lib/bpf/Build
@@ -1 +1 @@
-libbpf-y := libbpf.o bpf.o nlattr.o btf.o libbpf_errno.o str_error.o netlink.o bpf_prog_linfo.o libbpf_probes.o xsk.o
+libbpf-y := libbpf.o bpf.o nlattr.o btf.o libbpf_errno.o str_error.o netlink.o bpf_prog_linfo.o libbpf_probes.o xsk.o hashmap.o

diff --git a/tools/lib/bpf/hashmap.c b/tools/lib/bpf/hashmap.c
new file mode 100644 (file)
index 0000000..6122272
--- /dev/null
+++ b/tools/lib/bpf/hashmap.c
@@ -0,0 +1,229 @@
+// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
+
+/*
+ * Generic non-thread safe hash map implementation.
+ *
+ * Copyright (c) 2019 Facebook
+ */
+#include <stdint.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <errno.h>
+#include <linux/err.h>
+#include "hashmap.h"
+
+/* start with 4 buckets */
+#define HASHMAP_MIN_CAP_BITS 2
+
+static void hashmap_add_entry(struct hashmap_entry **pprev,
+                             struct hashmap_entry *entry)
+{
+       entry->next = *pprev;
+       *pprev = entry;
+}
+
+static void hashmap_del_entry(struct hashmap_entry **pprev,
+                             struct hashmap_entry *entry)
+{
+       *pprev = entry->next;
+       entry->next = NULL;
+}
+
+void hashmap__init(struct hashmap *map, hashmap_hash_fn hash_fn,
+                  hashmap_equal_fn equal_fn, void *ctx)
+{
+       map->hash_fn = hash_fn;
+       map->equal_fn = equal_fn;
+       map->ctx = ctx;
+
+       map->buckets = NULL;
+       map->cap = 0;
+       map->cap_bits = 0;
+       map->sz = 0;
+}
+
+struct hashmap *hashmap__new(hashmap_hash_fn hash_fn,
+                            hashmap_equal_fn equal_fn,
+                            void *ctx)
+{
+       struct hashmap *map = malloc(sizeof(struct hashmap));
+
+       if (!map)
+               return ERR_PTR(-ENOMEM);
+       hashmap__init(map, hash_fn, equal_fn, ctx);
+       return map;
+}
+
+void hashmap__clear(struct hashmap *map)
+{
+       free(map->buckets);
+       map->cap = map->cap_bits = map->sz = 0;
+}
+
+void hashmap__free(struct hashmap *map)
+{
+       if (!map)
+               return;
+
+       hashmap__clear(map);
+       free(map);
+}
+
+size_t hashmap__size(const struct hashmap *map)
+{
+       return map->sz;
+}
+
+size_t hashmap__capacity(const struct hashmap *map)
+{
+       return map->cap;
+}
+
+static bool hashmap_needs_to_grow(struct hashmap *map)
+{
+       /* grow if empty or more than 75% filled */
+       return (map->cap == 0) || ((map->sz + 1) * 4 / 3 > map->cap);
+}
+
+static int hashmap_grow(struct hashmap *map)
+{
+       struct hashmap_entry **new_buckets;
+       struct hashmap_entry *cur, *tmp;
+       size_t new_cap_bits, new_cap;
+       size_t h;
+       int bkt;
+
+       new_cap_bits = map->cap_bits + 1;
+       if (new_cap_bits < HASHMAP_MIN_CAP_BITS)
+               new_cap_bits = HASHMAP_MIN_CAP_BITS;
+
+       new_cap = 1UL << new_cap_bits;
+       new_buckets = calloc(new_cap, sizeof(new_buckets[0]));
+       if (!new_buckets)
+               return -ENOMEM;
+
+       hashmap__for_each_entry_safe(map, cur, tmp, bkt) {
+               h = hash_bits(map->hash_fn(cur->key, map->ctx), new_cap_bits);
+               hashmap_add_entry(&new_buckets[h], cur);
+       }
+
+       map->cap = new_cap;
+       map->cap_bits = new_cap_bits;
+       free(map->buckets);
+       map->buckets = new_buckets;
+
+       return 0;
+}
+
+static bool hashmap_find_entry(const struct hashmap *map,
+                              const void *key, size_t hash,
+                              struct hashmap_entry ***pprev,
+                              struct hashmap_entry **entry)
+{
+       struct hashmap_entry *cur, **prev_ptr;
+
+       if (!map->buckets)
+               return false;
+
+       for (prev_ptr = &map->buckets[hash], cur = *prev_ptr;
+            cur;
+            prev_ptr = &cur->next, cur = cur->next) {
+               if (map->equal_fn(cur->key, key, map->ctx)) {
+                       if (pprev)
+                               *pprev = prev_ptr;
+                       *entry = cur;
+                       return true;
+               }
+       }
+
+       return false;
+}
+
+int hashmap__insert(struct hashmap *map, const void *key, void *value,
+                   enum hashmap_insert_strategy strategy,
+                   const void **old_key, void **old_value)
+{
+       struct hashmap_entry *entry;
+       size_t h;
+       int err;
+
+       if (old_key)
+               *old_key = NULL;
+       if (old_value)
+               *old_value = NULL;
+
+       h = hash_bits(map->hash_fn(key, map->ctx), map->cap_bits);
+       if (strategy != HASHMAP_APPEND &&
+           hashmap_find_entry(map, key, h, NULL, &entry)) {
+               if (old_key)
+                       *old_key = entry->key;
+               if (old_value)
+                       *old_value = entry->value;
+
+               if (strategy == HASHMAP_SET || strategy == HASHMAP_UPDATE) {
+                       entry->key = key;
+                       entry->value = value;
+                       return 0;
+               } else if (strategy == HASHMAP_ADD) {
+                       return -EEXIST;
+               }
+       }
+
+       if (strategy == HASHMAP_UPDATE)
+               return -ENOENT;
+
+       if (hashmap_needs_to_grow(map)) {
+               err = hashmap_grow(map);
+               if (err)
+                       return err;
+               h = hash_bits(map->hash_fn(key, map->ctx), map->cap_bits);
+       }
+
+       entry = malloc(sizeof(struct hashmap_entry));
+       if (!entry)
+               return -ENOMEM;
+
+       entry->key = key;
+       entry->value = value;
+       hashmap_add_entry(&map->buckets[h], entry);
+       map->sz++;
+
+       return 0;
+}
+
+bool hashmap__find(const struct hashmap *map, const void *key, void **value)
+{
+       struct hashmap_entry *entry;
+       size_t h;
+
+       h = hash_bits(map->hash_fn(key, map->ctx), map->cap_bits);
+       if (!hashmap_find_entry(map, key, h, NULL, &entry))
+               return false;
+
+       if (value)
+               *value = entry->value;
+       return true;
+}
+
+bool hashmap__delete(struct hashmap *map, const void *key,
+                    const void **old_key, void **old_value)
+{
+       struct hashmap_entry **pprev, *entry;
+       size_t h;
+
+       h = hash_bits(map->hash_fn(key, map->ctx), map->cap_bits);
+       if (!hashmap_find_entry(map, key, h, &pprev, &entry))
+               return false;
+
+       if (old_key)
+               *old_key = entry->key;
+       if (old_value)
+               *old_value = entry->value;
+
+       hashmap_del_entry(pprev, entry);
+       free(entry);
+       map->sz--;
+
+       return true;
+}
+

diff --git a/tools/lib/bpf/hashmap.h b/tools/lib/bpf/hashmap.h
new file mode 100644 (file)
index 0000000..03748a7
--- /dev/null
+++ b/tools/lib/bpf/hashmap.h
@@ -0,0 +1,173 @@
+/* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
+
+/*
+ * Generic non-thread safe hash map implementation.
+ *
+ * Copyright (c) 2019 Facebook
+ */
+#ifndef __LIBBPF_HASHMAP_H
+#define __LIBBPF_HASHMAP_H
+
+#include <stdbool.h>
+#include <stddef.h>
+#include "libbpf_internal.h"
+
+static inline size_t hash_bits(size_t h, int bits)
+{
+       /* shuffle bits and return requested number of upper bits */
+       return (h * 11400714819323198485llu) >> (__WORDSIZE - bits);
+}
+
+typedef size_t (*hashmap_hash_fn)(const void *key, void *ctx);
+typedef bool (*hashmap_equal_fn)(const void *key1, const void *key2, void *ctx);
+
+struct hashmap_entry {
+       const void *key;
+       void *value;
+       struct hashmap_entry *next;
+};
+
+struct hashmap {
+       hashmap_hash_fn hash_fn;
+       hashmap_equal_fn equal_fn;
+       void *ctx;
+
+       struct hashmap_entry **buckets;
+       size_t cap;
+       size_t cap_bits;
+       size_t sz;
+};
+
+#define HASHMAP_INIT(hash_fn, equal_fn, ctx) { \
+       .hash_fn = (hash_fn),                   \
+       .equal_fn = (equal_fn),                 \
+       .ctx = (ctx),                           \
+       .buckets = NULL,                        \
+       .cap = 0,                               \
+       .cap_bits = 0,                          \
+       .sz = 0,                                \
+}
+
+void hashmap__init(struct hashmap *map, hashmap_hash_fn hash_fn,
+                  hashmap_equal_fn equal_fn, void *ctx);
+struct hashmap *hashmap__new(hashmap_hash_fn hash_fn,
+                            hashmap_equal_fn equal_fn,
+                            void *ctx);
+void hashmap__clear(struct hashmap *map);
+void hashmap__free(struct hashmap *map);
+
+size_t hashmap__size(const struct hashmap *map);
+size_t hashmap__capacity(const struct hashmap *map);
+
+/*
+ * Hashmap insertion strategy:
+ * - HASHMAP_ADD - only add key/value if key doesn't exist yet;
+ * - HASHMAP_SET - add key/value pair if key doesn't exist yet; otherwise,
+ *   update value;
+ * - HASHMAP_UPDATE - update value, if key already exists; otherwise, do
+ *   nothing and return -ENOENT;
+ * - HASHMAP_APPEND - always add key/value pair, even if key already exists.
+ *   This turns hashmap into a multimap by allowing multiple values to be
+ *   associated with the same key. Most useful read API for such hashmap is
+ *   hashmap__for_each_key_entry() iteration. If hashmap__find() is still
+ *   used, it will return last inserted key/value entry (first in a bucket
+ *   chain).
+ */
+enum hashmap_insert_strategy {
+       HASHMAP_ADD,
+       HASHMAP_SET,
+       HASHMAP_UPDATE,
+       HASHMAP_APPEND,
+};
+
+/*
+ * hashmap__insert() adds key/value entry w/ various semantics, depending on
+ * provided strategy value. If a given key/value pair replaced already
+ * existing key/value pair, both old key and old value will be returned
+ * through old_key and old_value to allow calling code do proper memory
+ * management.
+ */
+int hashmap__insert(struct hashmap *map, const void *key, void *value,
+                   enum hashmap_insert_strategy strategy,
+                   const void **old_key, void **old_value);
+
+static inline int hashmap__add(struct hashmap *map,
+                              const void *key, void *value)
+{
+       return hashmap__insert(map, key, value, HASHMAP_ADD, NULL, NULL);
+}
+
+static inline int hashmap__set(struct hashmap *map,
+                              const void *key, void *value,
+                              const void **old_key, void **old_value)
+{
+       return hashmap__insert(map, key, value, HASHMAP_SET,
+                              old_key, old_value);
+}
+
+static inline int hashmap__update(struct hashmap *map,
+                                 const void *key, void *value,
+                                 const void **old_key, void **old_value)
+{
+       return hashmap__insert(map, key, value, HASHMAP_UPDATE,
+                              old_key, old_value);
+}
+
+static inline int hashmap__append(struct hashmap *map,
+                                 const void *key, void *value)
+{
+       return hashmap__insert(map, key, value, HASHMAP_APPEND, NULL, NULL);
+}
+
+bool hashmap__delete(struct hashmap *map, const void *key,
+                    const void **old_key, void **old_value);
+
+bool hashmap__find(const struct hashmap *map, const void *key, void **value);
+
+/*
+ * hashmap__for_each_entry - iterate over all entries in hashmap
+ * @map: hashmap to iterate
+ * @cur: struct hashmap_entry * used as a loop cursor
+ * @bkt: integer used as a bucket loop cursor
+ */
+#define hashmap__for_each_entry(map, cur, bkt)                             \
+       for (bkt = 0; bkt < map->cap; bkt++)                                \
+               for (cur = map->buckets[bkt]; cur; cur = cur->next)
+
+/*
+ * hashmap__for_each_entry_safe - iterate over all entries in hashmap, safe
+ * against removals
+ * @map: hashmap to iterate
+ * @cur: struct hashmap_entry * used as a loop cursor
+ * @tmp: struct hashmap_entry * used as a temporary next cursor storage
+ * @bkt: integer used as a bucket loop cursor
+ */
+#define hashmap__for_each_entry_safe(map, cur, tmp, bkt)                   \
+       for (bkt = 0; bkt < map->cap; bkt++)                                \
+               for (cur = map->buckets[bkt];                               \
+                    cur && ({tmp = cur->next; true; });                    \
+                    cur = tmp)
+
+/*
+ * hashmap__for_each_key_entry - iterate over entries associated with given key
+ * @map: hashmap to iterate
+ * @cur: struct hashmap_entry * used as a loop cursor
+ * @key: key to iterate entries for
+ */
+#define hashmap__for_each_key_entry(map, cur, _key)                        \
+       for (cur = ({ size_t bkt = hash_bits(map->hash_fn((_key), map->ctx),\
+                                            map->cap_bits);                \
+                    map->buckets ? map->buckets[bkt] : NULL; });           \
+            cur;                                                           \
+            cur = cur->next)                                               \
+               if (map->equal_fn(cur->key, (_key), map->ctx))
+
+#define hashmap__for_each_key_entry_safe(map, cur, tmp, _key)              \
+       for (cur = ({ size_t bkt = hash_bits(map->hash_fn((_key), map->ctx),\
+                                            map->cap_bits);                \
+                    cur = map->buckets ? map->buckets[bkt] : NULL; });     \
+            cur && ({ tmp = cur->next; true; });                           \
+            cur = tmp)                                                     \
+               if (map->equal_fn(cur->key, (_key), map->ctx))
+
+#endif /* __LIBBPF_HASHMAP_H */