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
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 7132c6b..15e91a1 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -142,6 +142,8 @@
__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 @@
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 @@
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 @@
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_global_data,
bpf_object__probe_btf_func,
bpf_object__probe_btf_datasec,
+ bpf_object__probe_array_mmap,
};
int i, ret;
