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.
Acked-by: Song Liu <songliubraving@xxxxxx>
Acked-by: John Fastabend <john.fastabend@xxxxxxxxx>
Signed-off-by: Andrii Nakryiko <andriin@xxxxxx>
---
tools/lib/bpf/libbpf.c | 32 ++++++++++++++++++++++++++++++--
1 file changed, 30 insertions(+), 2 deletions(-)
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 96ef18cfeffb..7e2be1288fa1 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -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;
};
/*
@@ -856,8 +858,6 @@ 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;
@@ -865,6 +865,12 @@ 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) {
@@ -2160,6 +2166,27 @@ 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)
{
@@ -2168,6 +2195,7 @@ 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;
--
2.17.1
