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libbpf: Make global data internal arrays mmap()-able, if possible 

Add detection of BPF_F_MMAPABLE flag support for arrays and add it as an extra
flag to internal global data maps, if supported by kernel. This allows users
to memory-map global data and use it without BPF map operations, greatly
simplifying user experience.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Song Liu <songliubraving@fb.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20191117172806.2195367-5-andriin@fb.com
This commit is contained in:
Andrii Nakryiko 2019-11-17 09:28:05 -08:00 committed by Daniel Borkmann
parent fc9702273e
commit 7fe74b4362
1 changed files with 30 additions and 2 deletions
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32
tools/lib/bpf/libbpf.c
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@ -142,6 +142,8 @@ struct bpf_capabilities {
__u32 btf_func:1;
/* BTF_KIND_VAR and BTF_KIND_DATASEC support */
__u32 btf_datasec:1;
/* BPF_F_MMAPABLE is supported for arrays */
__u32 array_mmap:1;
};
/*
@ -857,8 +859,6 @@ bpf_object__init_internal_map(struct bpf_object *obj, enum libbpf_map_type type,
pr_warn("failed to alloc map name\n");
return -ENOMEM;
}
pr_debug("map '%s' (global data): at sec_idx %d, offset %zu.\n",
map_name, map->sec_idx, map->sec_offset);
def = &map->def;
def->type = BPF_MAP_TYPE_ARRAY;
@ -866,6 +866,12 @@ bpf_object__init_internal_map(struct bpf_object *obj, enum libbpf_map_type type,
def->value_size = data->d_size;
def->max_entries = 1;
def->map_flags = type == LIBBPF_MAP_RODATA ? BPF_F_RDONLY_PROG : 0;
if (obj->caps.array_mmap)
def->map_flags |= BPF_F_MMAPABLE;
pr_debug("map '%s' (global data): at sec_idx %d, offset %zu, flags %x.\n",
map_name, map->sec_idx, map->sec_offset, def->map_flags);
if (data_buff) {
*data_buff = malloc(data->d_size);
if (!*data_buff) {
@ -2161,6 +2167,27 @@ static int bpf_object__probe_btf_datasec(struct bpf_object *obj)
return 0;
}
static int bpf_object__probe_array_mmap(struct bpf_object *obj)
{
struct bpf_create_map_attr attr = {
.map_type = BPF_MAP_TYPE_ARRAY,
.map_flags = BPF_F_MMAPABLE,
.key_size = sizeof(int),
.value_size = sizeof(int),
.max_entries = 1,
};
int fd;
fd = bpf_create_map_xattr(&attr);
if (fd >= 0) {
obj->caps.array_mmap = 1;
close(fd);
return 1;
}
return 0;
}
static int
bpf_object__probe_caps(struct bpf_object *obj)
{
@ -2169,6 +2196,7 @@ bpf_object__probe_caps(struct bpf_object *obj)
bpf_object__probe_global_data,
bpf_object__probe_btf_func,
bpf_object__probe_btf_datasec,
bpf_object__probe_array_mmap,
};
int i, ret;