Regular BPF hash map is not mmap-able from user space. However, map-in-map
with outer map of type BPF_MAP_TYPE_HASH_OF_MAPS and mmap-able array as
inner map can perform similar operations as a mmap-able hash map. This
can be used by applications that benefit from fast accesses to some local
data.
Add a selftest to show this use case.
Signed-off-by: Song Liu <song@xxxxxxxxxx>
---
.../bpf/prog_tests/test_mmap_inner_array.c | 57 ++++++++++++++++++
.../selftests/bpf/progs/mmap_inner_array.c | 59 +++++++++++++++++++
2 files changed, 116 insertions(+)
create mode 100644 tools/testing/selftests/bpf/prog_tests/test_mmap_inner_array.c
create mode 100644 tools/testing/selftests/bpf/progs/mmap_inner_array.c
diff --git a/tools/testing/selftests/bpf/prog_tests/test_mmap_inner_array.c b/tools/testing/selftests/bpf/prog_tests/test_mmap_inner_array.c
new file mode 100644
index 000000000000..ce745776ed18
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/test_mmap_inner_array.c
@@ -0,0 +1,57 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2024 Meta Platforms, Inc. and affiliates. */
+#include <test_progs.h>
+#include <sys/mman.h>
+#include "mmap_inner_array.skel.h"
+
+void test_mmap_inner_array(void)
+{
+ const long page_size = sysconf(_SC_PAGE_SIZE);
+ struct mmap_inner_array *skel;
+ int inner_array_fd, err;
+ void *tmp;
+ __u64 *val;
+
+ skel = mmap_inner_array__open_and_load();
+
+ if (!ASSERT_OK_PTR(skel, "open_and_load"))
+ return;
+
+ inner_array_fd = bpf_map__fd(skel->maps.inner_array);
+ tmp = mmap(NULL, page_size, PROT_READ | PROT_WRITE, MAP_SHARED, inner_array_fd, 0);
+ if (!ASSERT_OK_PTR(tmp, "inner array mmap"))
+ goto out;
+ val = (void *)tmp;
+
+ err = mmap_inner_array__attach(skel);
+ if (!ASSERT_OK(err, "attach"))
+ goto out_unmap;
+
+ skel->bss->pid = getpid();
+ usleep(1);
+
+ /* pid is set, pid_match == true and outer_map_match == false */
+ ASSERT_TRUE(skel->bss->pid_match, "pid match 1");
+ ASSERT_FALSE(skel->bss->outer_map_match, "outer map match 1");
+ ASSERT_FALSE(skel->bss->done, "done 1");
+ ASSERT_EQ(*val, 0, "value match 1");
+
+ err = bpf_map__update_elem(skel->maps.outer_map,
+ &skel->bss->pid, sizeof(skel->bss->pid),
+ &inner_array_fd, sizeof(inner_array_fd),
+ BPF_ANY);
+ if (!ASSERT_OK(err, "update elem"))
+ goto out_unmap;
+ usleep(1);
+
+ /* outer map key is set, outer_map_match == true */
+ ASSERT_TRUE(skel->bss->pid_match, "pid match 2");
+ ASSERT_TRUE(skel->bss->outer_map_match, "outer map match 2");
+ ASSERT_TRUE(skel->bss->done, "done 2");
+ ASSERT_EQ(*val, skel->data->match_value, "value match 2");
+
+out_unmap:
+ munmap(tmp, page_size);
+out:
+ mmap_inner_array__destroy(skel);
+}
diff --git a/tools/testing/selftests/bpf/progs/mmap_inner_array.c b/tools/testing/selftests/bpf/progs/mmap_inner_array.c
new file mode 100644
index 000000000000..db8ca2aa4347
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/mmap_inner_array.c
@@ -0,0 +1,59 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2024 Meta Platforms, Inc. and affiliates. */
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+#include "bpf_misc.h"
+#include "bpf_experimental.h"
+
+char _license[] SEC("license") = "GPL";
+
+struct inner_array_type {
+ __uint(type, BPF_MAP_TYPE_ARRAY);
+ __uint(map_flags, BPF_F_MMAPABLE);
+ __type(key, __u32);
+ __type(value, __u64);
+ __uint(max_entries, 1);
+} inner_array SEC(".maps");
+
+struct {
+ __uint(type, BPF_MAP_TYPE_HASH_OF_MAPS);
+ __uint(key_size, 4);
+ __uint(value_size, 4);
+ __uint(max_entries, 1);
+ __array(values, struct inner_array_type);
+} outer_map SEC(".maps");
+
+int pid = 0;
+__u64 match_value = 0x13572468;
+bool done = false;
+bool pid_match = false;
+bool outer_map_match = false;
+
+SEC("fentry/" SYS_PREFIX "sys_nanosleep")
+int add_to_list_in_inner_array(void *ctx)
+{
+ __u32 curr_pid, zero = 0;
+ struct bpf_map *map;
+ __u64 *value;
+
+ curr_pid = (u32)bpf_get_current_pid_tgid();
+ if (done || curr_pid != pid)
+ return 0;
+
+ pid_match = true;
+ map = bpf_map_lookup_elem(&outer_map, &curr_pid);
+ if (!map)
+ return 0;
+
+ outer_map_match = true;
+ value = bpf_map_lookup_elem(map, &zero);
+ if (!value)
+ return 0;
+
+ *value = match_value;
+ done = true;
+ return 0;
+}
--
2.43.0
