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bpf: add queue and stack maps

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Queue/stack maps implement a FIFO/LIFO data storage for ebpf programs.
These maps support peek, pop and push operations that are exposed to eBPF
programs through the new bpf_map[peek/pop/push] helpers.  Those operations
are exposed to userspace applications through the already existing
syscalls in the following way:

BPF_MAP_LOOKUP_ELEM            -> peek
BPF_MAP_LOOKUP_AND_DELETE_ELEM -> pop
BPF_MAP_UPDATE_ELEM            -> push

Queue/stack maps are implemented using a buffer, tail and head indexes,
hence BPF_F_NO_PREALLOC is not supported.

As opposite to other maps, queue and stack do not use RCU for protecting
maps values, the bpf_map[peek/pop] have a ARG_PTR_TO_UNINIT_MAP_VALUE
argument that is a pointer to a memory zone where to save the value of a
map.  Basically the same as ARG_PTR_TO_UNINIT_MEM, but the size has not
be passed as an extra argument.

Our main motivation for implementing queue/stack maps was to keep track
of a pool of elements, like network ports in a SNAT, however we forsee
other use cases, like for exampling saving last N kernel events in a map
and then analysing from userspace.

Signed-off-by: Mauricio Vasquez B <mauricio.vasquez@polito.it>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Mauricio Vasquez B
2018-10-18 15:16:25 +02:00
committed by Alexei Starovoitov
parent 2ea864c58f
commit f1a2e44a3a
10 changed files with 401 additions and 3 deletions
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29
include/uapi/linux/bpf.h
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@@ -128,6 +128,8 @@ enum bpf_map_type {
BPF_MAP_TYPE_CGROUP_STORAGE,
BPF_MAP_TYPE_REUSEPORT_SOCKARRAY,
BPF_MAP_TYPE_PERCPU_CGROUP_STORAGE,
BPF_MAP_TYPE_QUEUE,
BPF_MAP_TYPE_STACK,
};
enum bpf_prog_type {
@@ -462,6 +464,28 @@ union bpf_attr {
* Return
* 0 on success, or a negative error in case of failure.
*
* int bpf_map_push_elem(struct bpf_map *map, const void *value, u64 flags)
* Description
* Push an element *value* in *map*. *flags* is one of:
*
* **BPF_EXIST**
* If the queue/stack is full, the oldest element is removed to
* make room for this.
* Return
* 0 on success, or a negative error in case of failure.
*
* int bpf_map_pop_elem(struct bpf_map *map, void *value)
* Description
* Pop an element from *map*.
* Return
* 0 on success, or a negative error in case of failure.
*
* int bpf_map_peek_elem(struct bpf_map *map, void *value)
* Description
* Get an element from *map* without removing it.
* Return
* 0 on success, or a negative error in case of failure.
*
* int bpf_probe_read(void *dst, u32 size, const void *src)
* Description
* For tracing programs, safely attempt to read *size* bytes from
@@ -2303,7 +2327,10 @@ union bpf_attr {
FN(skb_ancestor_cgroup_id), \
FN(sk_lookup_tcp), \
FN(sk_lookup_udp), \
FN(sk_release),
FN(sk_release), \
FN(map_push_elem), \
FN(map_pop_elem), \
FN(map_peek_elem),
/* integer value in 'imm' field of BPF_CALL instruction selects which helper
* function eBPF program intends to call