Introduce bpf_link__update_map(), which allows to atomically update
underlying struct_ops implementation for given struct_ops BPF link.
Also add old_map_fd to struct bpf_link_update_opts to handle
BPF_F_REPLACE feature.
Signed-off-by: Kui-Feng Lee <kuifeng@xxxxxxxx>
---
tools/lib/bpf/bpf.c | 4 ++++
tools/lib/bpf/bpf.h | 3 ++-
tools/lib/bpf/libbpf.c | 35 +++++++++++++++++++++++++++++++++++
tools/lib/bpf/libbpf.h | 1 +
tools/lib/bpf/libbpf.map | 1 +
5 files changed, 43 insertions(+), 1 deletion(-)
diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index e750b6f5fcc3..5e88f924bb6d 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -794,11 +794,15 @@ int bpf_link_update(int link_fd, int new_prog_fd,
if (!OPTS_VALID(opts, bpf_link_update_opts))
return libbpf_err(-EINVAL);
+ if (OPTS_GET(opts, old_prog_fd, 0) && OPTS_GET(opts, old_map_fd, 0))
+ return libbpf_err(-EINVAL);
+
memset(&attr, 0, attr_sz);
attr.link_update.link_fd = link_fd;
attr.link_update.new_prog_fd = new_prog_fd;
attr.link_update.flags = OPTS_GET(opts, flags, 0);
attr.link_update.old_prog_fd = OPTS_GET(opts, old_prog_fd, 0);
+ attr.link_update.old_map_fd = OPTS_GET(opts, old_map_fd, 0);
ret = sys_bpf(BPF_LINK_UPDATE, &attr, attr_sz);
return libbpf_err_errno(ret);
diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
index f0f786373238..b073e73439ef 100644
--- a/tools/lib/bpf/bpf.h
+++ b/tools/lib/bpf/bpf.h
@@ -336,8 +336,9 @@ struct bpf_link_update_opts {
size_t sz; /* size of this struct for forward/backward compatibility */
__u32 flags; /* extra flags */
__u32 old_prog_fd; /* expected old program FD */
+ __u32 old_map_fd; /* expected old map FD */
};
-#define bpf_link_update_opts__last_field old_prog_fd
+#define bpf_link_update_opts__last_field old_map_fd
LIBBPF_API int bpf_link_update(int link_fd, int new_prog_fd,
const struct bpf_link_update_opts *opts);
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 4ff82baba0ea..2b5ea2500b80 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -11677,6 +11677,41 @@ struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map)
return &link->link;
}
+/*
+ * Swap the back struct_ops of a link with a new struct_ops map.
+ */
+int bpf_link__update_map(struct bpf_link *link, const struct bpf_map *map)
+{
+ struct bpf_link_struct_ops *st_ops_link;
+ __u32 zero = 0;
+ int err;
+
+ if (!bpf_map__is_struct_ops(map) || map->fd < 0)
+ return -EINVAL;
+
+ st_ops_link = container_of(link, struct bpf_link_struct_ops, link);
+ /* Ensure the type of a link is correct */
+ if (st_ops_link->map_fd < 0)
+ return -EINVAL;
+
+ err = bpf_map_update_elem(map->fd, &zero, map->st_ops->kern_vdata, 0);
+ /* It can be EBUSY if the map has been used to create or
+ * update a link before. We don't allow updating the value of
+ * a struct_ops once it is set. That ensures that the value
+ * never changed. So, it is safe to skip EBUSY.
+ */
+ if (err && err != -EBUSY)
+ return err;
+
+ err = bpf_link_update(link->fd, map->fd, NULL);
+ if (err < 0)
+ return err;
+
+ st_ops_link->map_fd = map->fd;
+
+ return 0;
+}
+
typedef enum bpf_perf_event_ret (*bpf_perf_event_print_t)(struct perf_event_header *hdr,
void *private_data);
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index db4992a036f8..1615e55e2e79 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -719,6 +719,7 @@ bpf_program__attach_freplace(const struct bpf_program *prog,
struct bpf_map;
LIBBPF_API struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map);
+LIBBPF_API int bpf_link__update_map(struct bpf_link *link, const struct bpf_map *map);
struct bpf_iter_attach_opts {
size_t sz; /* size of this struct for forward/backward compatibility */
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 50dde1f6521e..a5aa3a383d69 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -386,6 +386,7 @@ LIBBPF_1.1.0 {
LIBBPF_1.2.0 {
global:
bpf_btf_get_info_by_fd;
+ bpf_link__update_map;
bpf_link_get_info_by_fd;
bpf_map_get_info_by_fd;
bpf_prog_get_info_by_fd;
--
2.34.1
