[bpf-next,3/4] libbpf: Add support for MAP_GET_NUM_ENTRIES command

Commit Message

Charalampos Stylianopoulos Jan. 6, 2025, 2:53 p.m. UTC

Extend the libbpf API to provide support for getting the number of
entries in a map.

Co-developed-by: Nick Zavaritsky <[e-mail]>
Signed-off-by: Nick Zavaritsky <[e-mail]>
Signed-off-by: Charalampos Stylianopoulos <[e-mail]>
---
 tools/include/uapi/linux/bpf.h | 17 +++++++++++++++++
 tools/lib/bpf/bpf.c            | 16 ++++++++++++++++
 tools/lib/bpf/bpf.h            |  2 ++
 tools/lib/bpf/libbpf.map       |  1 +
 4 files changed, 36 insertions(+)

Patch

diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 2acf9b336371..f5c7adea1387 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -903,6 +903,17 @@  union bpf_iter_link_info {
  *		A new file descriptor (a nonnegative integer), or -1 if an
  *		error occurred (in which case, *errno* is set appropriately).
  *
+ * BPF_MAP_GET_NUM_ENTRIES
+ *	Description
+ *		Get the number of entries currently present in the map.
+ *
+ *		This operation is supported only for a subset of maps. If the
+ *		map is not supported, the operation returns **EOPNOTSUPP**.
+ *
+ *	Return
+ *		Returns zero on success. On error, -1 is returned and *errno*
+ *		is set appropriately.
+ *
  * NOTES
  *	eBPF objects (maps and programs) can be shared between processes.
  *
@@ -958,6 +969,7 @@  enum bpf_cmd {
 	BPF_LINK_DETACH,
 	BPF_PROG_BIND_MAP,
 	BPF_TOKEN_CREATE,
+	BPF_MAP_GET_NUM_ENTRIES,
 	__MAX_BPF_CMD,
 };
 
@@ -1837,6 +1849,11 @@  union bpf_attr {
 		__u32		bpffs_fd;
 	} token_create;
 
+	struct { /* struct used by BPF_MAP_GET_NUM_ENTRIES command*/
+		__u32 map_fd;
+		__u32 num_entries;
+	} map_get_num_entries;
+
 } __attribute__((aligned(8)));
 
 /* The description below is an attempt at providing documentation to eBPF
diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index 359f73ead613..c91f43690624 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -1330,3 +1330,19 @@  int bpf_token_create(int bpffs_fd, struct bpf_token_create_opts *opts)
 	fd = sys_bpf_fd(BPF_TOKEN_CREATE, &attr, attr_sz);
 	return libbpf_err_errno(fd);
 }
+
+int bpf_map_get_num_entries(int fd, unsigned int *num_entries)
+{
+	const size_t attr_sz = offsetofend(union bpf_attr, map_get_num_entries);
+	union bpf_attr attr;
+	int ret;
+
+	memset(&attr, 0, attr_sz);
+	attr.map_get_num_entries.map_fd = fd;
+
+	ret = sys_bpf(BPF_MAP_GET_NUM_ENTRIES, &attr, attr_sz);
+	if (!ret)
+		*num_entries = attr.map_get_num_entries.num_entries;
+
+	return libbpf_err_errno(ret);
+}
diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
index 435da95d2058..efa5a092acc9 100644
--- a/tools/lib/bpf/bpf.h
+++ b/tools/lib/bpf/bpf.h
@@ -653,6 +653,8 @@  struct bpf_prog_bind_opts {
 LIBBPF_API int bpf_prog_bind_map(int prog_fd, int map_fd,
 				 const struct bpf_prog_bind_opts *opts);
 
+LIBBPF_API int bpf_map_get_num_entries(int fd, unsigned int *num_entries);
+
 struct bpf_test_run_opts {
 	size_t sz; /* size of this struct for forward/backward compatibility */
 	const void *data_in; /* optional */
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index a8b2936a1646..63dbad55cc2d 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -436,4 +436,5 @@  LIBBPF_1.6.0 {
 		bpf_linker__add_buf;
 		bpf_linker__add_fd;
 		bpf_linker__new_fd;
+		bpf_map_get_num_entries;
 } LIBBPF_1.5.0;