bpftool: Register struct_ops with a link.

You can include an optional path after specifying the object name for the
'struct_ops register' subcommand.

Since the commit 226bc6ae6405 ("Merge branch 'Transit between BPF TCP
congestion controls.'") has been accepted, it is now possible to create a
link for a struct_ops. This can be done by defining a struct_ops in
SEC(".struct_ops.link") to make libbpf returns a real link. If we don't pin
the links before leaving bpftool, they will disappear. To instruct bpftool
to pin the links in a directory with the names of the maps, we need to
provide the path of that directory.

Signed-off-by: Kui-Feng Lee <kuifeng@meta.com>
Reviewed-by: Quentin Monnet <quentin@isovalent.com>
Link: https://lore.kernel.org/r/20230420002822.345222-1-kuifeng@meta.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/tools/bpf/bpftool/common.c b/tools/bpf/bpftool/common.c
index 5a73ccf..1360c82 100644 (file)
--- a/tools/bpf/bpftool/common.c
+++ b/tools/bpf/bpftool/common.c
@@ -1091,3 +1091,17 @@ const char *bpf_attach_type_input_str(enum bpf_attach_type t)
        default:        return libbpf_bpf_attach_type_str(t);
        }
 }
+
+int pathname_concat(char *buf, int buf_sz, const char *path,
+                   const char *name)
+{
+       int len;
+
+       len = snprintf(buf, buf_sz, "%s/%s", path, name);
+       if (len < 0)
+               return -EINVAL;
+       if (len >= buf_sz)
+               return -ENAMETOOLONG;
+
+       return 0;
+}

diff --git a/tools/bpf/bpftool/main.h b/tools/bpf/bpftool/main.h
index 00d11ca..9a95788 100644 (file)
--- a/tools/bpf/bpftool/main.h
+++ b/tools/bpf/bpftool/main.h
@@ -264,4 +264,7 @@ static inline bool hashmap__empty(struct hashmap *map)
        return map ? hashmap__size(map) == 0 : true;
 }
 
+int pathname_concat(char *buf, int buf_sz, const char *path,
+                   const char *name);
+
 #endif

diff --git a/tools/bpf/bpftool/prog.c b/tools/bpf/bpftool/prog.c
index e5b613a..91b6075 100644 (file)
--- a/tools/bpf/bpftool/prog.c
+++ b/tools/bpf/bpftool/prog.c
@@ -1476,19 +1476,6 @@ auto_attach_program(struct bpf_program *prog, const char *path)
        return err;
 }
 
-static int pathname_concat(char *buf, size_t buf_sz, const char *path, const char *name)
-{
-       int len;
-
-       len = snprintf(buf, buf_sz, "%s/%s", path, name);
-       if (len < 0)
-               return -EINVAL;
-       if ((size_t)len >= buf_sz)
-               return -ENAMETOOLONG;
-
-       return 0;
-}
-
 static int
 auto_attach_programs(struct bpf_object *obj, const char *path)
 {

diff --git a/tools/bpf/bpftool/struct_ops.c b/tools/bpf/bpftool/struct_ops.c
index b389f48..57c3da7 100644 (file)
--- a/tools/bpf/bpftool/struct_ops.c
+++ b/tools/bpf/bpftool/struct_ops.c
@@ -475,21 +475,44 @@ static int do_unregister(int argc, char **argv)
        return cmd_retval(&res, true);
 }
 
+static int pin_link(struct bpf_link *link, const char *pindir,
+                   const char *name)
+{
+       char pinfile[PATH_MAX];
+       int err;
+
+       err = pathname_concat(pinfile, sizeof(pinfile), pindir, name);
+       if (err)
+               return -1;
+
+       return bpf_link__pin(link, pinfile);
+}
+
 static int do_register(int argc, char **argv)
 {
        LIBBPF_OPTS(bpf_object_open_opts, open_opts);
+       __u32 link_info_len = sizeof(struct bpf_link_info);
+       struct bpf_link_info link_info = {};
        struct bpf_map_info info = {};
        __u32 info_len = sizeof(info);
        int nr_errs = 0, nr_maps = 0;
+       const char *linkdir = NULL;
        struct bpf_object *obj;
        struct bpf_link *link;
        struct bpf_map *map;
        const char *file;
 
-       if (argc != 1)
+       if (argc != 1 && argc != 2)
                usage();
 
        file = GET_ARG();
+       if (argc == 1)
+               linkdir = GET_ARG();
+
+       if (linkdir && mount_bpffs_for_pin(linkdir)) {
+               p_err("can't mount bpffs for pinning");
+               return -1;
+       }
 
        if (verifier_logs)
                /* log_level1 + log_level2 + stats, but not stable UAPI */
@@ -519,21 +542,44 @@ static int do_register(int argc, char **argv)
                }
                nr_maps++;
 
-               bpf_link__disconnect(link);
-               bpf_link__destroy(link);
-
-               if (!bpf_map_get_info_by_fd(bpf_map__fd(map), &info,
-                                           &info_len))
-                       p_info("Registered %s %s id %u",
-                              get_kern_struct_ops_name(&info),
-                              bpf_map__name(map),
-                              info.id);
-               else
+               if (bpf_map_get_info_by_fd(bpf_map__fd(map), &info,
+                                          &info_len)) {
                        /* Not p_err.  The struct_ops was attached
                         * successfully.
                         */
                        p_info("Registered %s but can't find id: %s",
                               bpf_map__name(map), strerror(errno));
+                       goto clean_link;
+               }
+               if (!(bpf_map__map_flags(map) & BPF_F_LINK)) {
+                       p_info("Registered %s %s id %u",
+                              get_kern_struct_ops_name(&info),
+                              info.name,
+                              info.id);
+                       goto clean_link;
+               }
+               if (bpf_link_get_info_by_fd(bpf_link__fd(link),
+                                           &link_info,
+                                           &link_info_len)) {
+                       p_err("Registered %s but can't find link id: %s",
+                             bpf_map__name(map), strerror(errno));
+                       nr_errs++;
+                       goto clean_link;
+               }
+               if (linkdir && pin_link(link, linkdir, info.name)) {
+                       p_err("can't pin link %u for %s: %s",
+                             link_info.id, info.name,
+                             strerror(errno));
+                       nr_errs++;
+                       goto clean_link;
+               }
+               p_info("Registered %s %s map id %u link id %u",
+                      get_kern_struct_ops_name(&info),
+                      info.name, info.id, link_info.id);
+
+clean_link:
+               bpf_link__disconnect(link);
+               bpf_link__destroy(link);
        }
 
        bpf_object__close(obj);
@@ -562,7 +608,7 @@ static int do_help(int argc, char **argv)
        fprintf(stderr,
                "Usage: %1$s %2$s { show | list } [STRUCT_OPS_MAP]\n"
                "       %1$s %2$s dump [STRUCT_OPS_MAP]\n"
-               "       %1$s %2$s register OBJ\n"
+               "       %1$s %2$s register OBJ [LINK_DIR]\n"
                "       %1$s %2$s unregister STRUCT_OPS_MAP\n"
                "       %1$s %2$s help\n"
                "\n"