Commit 28fbcfa0 authored by Alexei Starovoitov's avatar Alexei Starovoitov Committed by David S. Miller
Browse files

bpf: add array type of eBPF maps 



add new map type BPF_MAP_TYPE_ARRAY and its implementation

- optimized for fastest possible lookup()
  . in the future verifier/JIT may recognize lookup() with constant key
    and optimize it into constant pointer. Can optimize non-constant
    key into direct pointer arithmetic as well, since pointers and
    value_size are constant for the life of the eBPF program.
    In other words array_map_lookup_elem() may be 'inlined' by verifier/JIT
    while preserving concurrent access to this map from user space

- two main use cases for array type:
  . 'global' eBPF variables: array of 1 element with key=0 and value is a
    collection of 'global' variables which programs can use to keep the state
    between events
  . aggregation of tracing events into fixed set of buckets

- all array elements pre-allocated and zero initialized at init time

- key as an index in array and can only be 4 byte

- map_delete_elem() returns EINVAL, since elements cannot be deleted

- map_update_elem() replaces elements in an non-atomic way
  (for atomic updates hashtable type should be used instead)

Signed-off-by: default avatarAlexei Starovoitov <ast@plumgrid.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 0f8e4bd8

include/uapi/linux/bpf.h

+1 −0
Original line number Diff line number Diff line
@@ -112,6 +112,7 @@ enum bpf_cmd { 
enum bpf_map_type {

	BPF_MAP_TYPE_UNSPEC,

	BPF_MAP_TYPE_HASH,

	BPF_MAP_TYPE_ARRAY,

};



enum bpf_prog_type {

kernel/bpf/Makefile

+1 −1
Original line number Diff line number Diff line 
obj-y := core.o

obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o hashtab.o

obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o hashtab.o arraymap.o

ifdef CONFIG_TEST_BPF

obj-$(CONFIG_BPF_SYSCALL) += test_stub.o

endif

kernel/bpf/arraymap.c

0 → 100644
+151 −0
Original line number Diff line number Diff line 
/* Copyright (c) 2011-2014 PLUMgrid, http://plumgrid.com

 *

 * This program is free software; you can redistribute it and/or

 * modify it under the terms of version 2 of the GNU General Public

 * License as published by the Free Software Foundation.

 *

 * 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.

 */

#include <linux/bpf.h>

#include <linux/err.h>

#include <linux/vmalloc.h>

#include <linux/slab.h>

#include <linux/mm.h>



struct bpf_array {

	struct bpf_map map;

	u32 elem_size;

	char value[0] __aligned(8);

};



/* Called from syscall */

static struct bpf_map *array_map_alloc(union bpf_attr *attr)

{

	struct bpf_array *array;

	u32 elem_size;



	/* check sanity of attributes */

	if (attr->max_entries == 0 || attr->key_size != 4 ||

	    attr->value_size == 0)

		return ERR_PTR(-EINVAL);



	elem_size = round_up(attr->value_size, 8);



	/* allocate all map elements and zero-initialize them */

	array = kzalloc(sizeof(*array) + attr->max_entries * elem_size,

			GFP_USER | __GFP_NOWARN);

	if (!array) {

		array = vzalloc(array->map.max_entries * array->elem_size);

		if (!array)

			return ERR_PTR(-ENOMEM);

	}



	/* copy mandatory map attributes */

	array->map.key_size = attr->key_size;

	array->map.value_size = attr->value_size;

	array->map.max_entries = attr->max_entries;



	array->elem_size = elem_size;



	return &array->map;



}



/* Called from syscall or from eBPF program */

static void *array_map_lookup_elem(struct bpf_map *map, void *key)

{

	struct bpf_array *array = container_of(map, struct bpf_array, map);

	u32 index = *(u32 *)key;



	if (index >= array->map.max_entries)

		return NULL;



	return array->value + array->elem_size * index;

}



/* Called from syscall */

static int array_map_get_next_key(struct bpf_map *map, void *key, void *next_key)

{

	struct bpf_array *array = container_of(map, struct bpf_array, map);

	u32 index = *(u32 *)key;

	u32 *next = (u32 *)next_key;



	if (index >= array->map.max_entries) {

		*next = 0;

		return 0;

	}



	if (index == array->map.max_entries - 1)

		return -ENOENT;



	*next = index + 1;

	return 0;

}



/* Called from syscall or from eBPF program */

static int array_map_update_elem(struct bpf_map *map, void *key, void *value,

				 u64 map_flags)

{

	struct bpf_array *array = container_of(map, struct bpf_array, map);

	u32 index = *(u32 *)key;



	if (map_flags > BPF_EXIST)

		/* unknown flags */

		return -EINVAL;



	if (index >= array->map.max_entries)

		/* all elements were pre-allocated, cannot insert a new one */

		return -E2BIG;



	if (map_flags == BPF_NOEXIST)

		/* all elemenets already exist */

		return -EEXIST;



	memcpy(array->value + array->elem_size * index, value, array->elem_size);

	return 0;

}



/* Called from syscall or from eBPF program */

static int array_map_delete_elem(struct bpf_map *map, void *key)

{

	return -EINVAL;

}



/* Called when map->refcnt goes to zero, either from workqueue or from syscall */

static void array_map_free(struct bpf_map *map)

{

	struct bpf_array *array = container_of(map, struct bpf_array, map);



	/* at this point bpf_prog->aux->refcnt == 0 and this map->refcnt == 0,

	 * so the programs (can be more than one that used this map) were

	 * disconnected from events. Wait for outstanding programs to complete

	 * and free the array

	 */

	synchronize_rcu();



	kvfree(array);

}



static struct bpf_map_ops array_ops = {

	.map_alloc = array_map_alloc,

	.map_free = array_map_free,

	.map_get_next_key = array_map_get_next_key,

	.map_lookup_elem = array_map_lookup_elem,

	.map_update_elem = array_map_update_elem,

	.map_delete_elem = array_map_delete_elem,

};



static struct bpf_map_type_list tl = {

	.ops = &array_ops,

	.type = BPF_MAP_TYPE_ARRAY,

};



static int __init register_array_map(void)

{

	bpf_register_map_type(&tl);

	return 0;

}

late_initcall(register_array_map);

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