Merge branch 'bpf_metadata'

Stanislav Fomichev says:

====================
Currently, if a user wants to store arbitrary metadata for an eBPF
program, for example, the program build commit hash or version, they
could store it in a map, and conveniently libbpf uses .data section to
populate an internal map. However, if the program does not actually
reference the map, then the map would be de-refcounted and freed.

This patch set introduces a new syscall BPF_PROG_BIND_MAP to add a map
to a program's used_maps, even if the program instructions does not
reference the map.

libbpf is extended to always BPF_PROG_BIND_MAP .rodata section so the
metadata is kept in place.
bpftool is also extended to print metadata in the 'bpftool prog' list.

The variable is considered metadata if it starts with the
magic 'bpf_metadata_' prefix; everything after the prefix is the
metadata name.

An example use of this would be BPF C file declaring:

  volatile const char bpf_metadata_commit_hash[] SEC(".rodata") = "abcdef123456";

and bpftool would emit:

  $ bpftool prog
  [...]
        metadata:
                commit_hash = "abcdef123456"

v6 changes:
* libbpf: drop FEAT_GLOBAL_DATA from probe_prog_bind_map (Andrii Nakryiko)
* bpftool: combine find_metadata_map_id & find_metadata;
  drops extra bpf_map_get_fd_by_id and bpf_map_get_fd_by_id (Andrii Nakryiko)
* bpftool: use strncmp instead of strstr (Andrii Nakryiko)
* bpftool: memset(map_info) and extra empty line (Andrii Nakryiko)

v5 changes:
* selftest: verify that prog holds rodata (Andrii Nakryiko)
* selftest: use volatile for metadata (Andrii Nakryiko)
* bpftool: use sizeof in BPF_METADATA_PREFIX_LEN (Andrii Nakryiko)
* bpftool: new find_metadata that does map lookup (Andrii Nakryiko)
* libbpf: don't generalize probe_create_global_data (Andrii Nakryiko)
* libbpf: use OPTS_VALID in bpf_prog_bind_map (Andrii Nakryiko)
* libbpf: keep LIBBPF_0.2.0 sorted (Andrii Nakryiko)

v4 changes:
* Don't return EEXIST from syscall if already bound (Andrii Nakryiko)
* Removed --metadata argument (Andrii Nakryiko)
* Removed custom .metadata section (Alexei Starovoitov)
* Addressed Andrii's suggestions about btf helpers and vsi (Andrii Nakryiko)
* Moved bpf_prog_find_metadata into bpftool (Alexei Starovoitov)

v3 changes:
* API changes for bpf_prog_find_metadata (Toke Høiland-Jørgensen)

v2 changes:
* Made struct bpf_prog_bind_opts in libbpf so flags is optional.
* Deduped probe_kern_global_data and probe_prog_bind_map into a common
  helper.
* Added comment regarding why EEXIST is ignored in libbpf bind map.
* Froze all LIBBPF_MAP_METADATA internal maps.
* Moved bpf_prog_bind_map into new LIBBPF_0.1.1 in libbpf.map.
* Added p_err() calls on error cases in bpftool show_prog_metadata.
* Reverse christmas tree coding style in bpftool show_prog_metadata.
* Made bpftool gen skeleton recognize .metadata as an internal map and
  generate datasec definition in skeleton.
* Added C test using skeleton to see asset that the metadata is what we
  expect and rebinding causes EEXIST.

v1 changes:
* Fixed a few missing unlocks, and missing close while iterating map fds.
* Move mutex initialization to right after prog aux allocation, and mutex
  destroy to right after prog aux free.
* s/ADD_MAP/BIND_MAP/
* Use mutex only instead of RCU to protect the used_map array & count.

Cc: YiFei Zhu <zhuyifei1999@gmail.com>
====================

Acked-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

2 files changed, 8 insertions, 0 deletions

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index c6d9f2c444f4..5dcce0364634 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -751,6 +751,7 @@ struct bpf_prog_aux {
 	struct bpf_ksym ksym;
 	const struct bpf_prog_ops *ops;
 	struct bpf_map **used_maps;
+	struct mutex used_maps_mutex; /* mutex for used_maps and used_map_cnt */
 	struct bpf_prog *prog;
 	struct user_struct *user;
 	u64 load_time; /* ns since boottime */
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 7dd314176df7..a22812561064 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -124,6 +124,7 @@ enum bpf_cmd {
 	BPF_ENABLE_STATS,
 	BPF_ITER_CREATE,
 	BPF_LINK_DETACH,
+	BPF_PROG_BIND_MAP,
 };
 
 enum bpf_map_type {
@@ -658,6 +659,12 @@ union bpf_attr {
 		__u32		flags;
 	} iter_create;
 
+	struct { /* struct used by BPF_PROG_BIND_MAP command */
+		__u32		prog_fd;
+		__u32		map_fd;
+		__u32		flags;		/* extra flags */
+	} prog_bind_map;
+
 } __attribute__((aligned(8)));
 
 /* The description below is an attempt at providing documentation to eBPF