[PATCH v2 bpf-next 28/30] libbpf: support BPF token path setting through LIBBPF_BPF_TOKEN_PATH envvar

[Andrii Nakryiko]

To allow external admin authority to override default BPF FS location
(/sys/fs/bpf) for implicit BPF token creation, teach libbpf to recognize
LIBBPF_BPF_TOKEN_PATH envvar. If it is specified and user application
didn't explicitly specify bpf_token_path option, it will be treated
exactly like bpf_token_path option, overriding default /sys/fs/bpf
location and making BPF token mandatory.

Suggested-by: Alexei Starovoitov <ast at kernel.org>
Signed-off-by: Andrii Nakryiko <andrii at kernel.org>
---
 tools/lib/bpf/libbpf.c | 6 ++++++
 tools/lib/bpf/libbpf.h | 8 ++++++++
 2 files changed, 14 insertions(+)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index a2866329d8f2..38a0e1e9a472 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -7585,6 +7585,12 @@ static struct bpf_object *bpf_object_open(const char *path, const void *obj_buf,
 		return ERR_PTR(-EINVAL);
 
 	token_path = OPTS_GET(opts, bpf_token_path, NULL);
+	/* if user didn't specify bpf_token_path explicitly, check if
+	 * LIBBPF_BPF_TOKEN_PATH envvar was set and treat it as bpf_token_path
+	 * option
+	 */
+	if (!token_path)
+		token_path = getenv("LIBBPF_BPF_TOKEN_PATH");
 	if (token_path && strlen(token_path) >= PATH_MAX)
 		return ERR_PTR(-ENAMETOOLONG);
 
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 535ae15ed493..5723cbbfcc41 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -183,6 +183,14 @@ struct bpf_object_open_opts {
 	 * that accept BPF token (e.g., map creation, BTF and program loads,
 	 * etc) automatically within instantiated BPF object.
 	 *
+	 * If bpf_token_path is not specified, libbpf will consult
+	 * LIBBPF_BPF_TOKEN_PATH environment variable. If set, it will be
+	 * taken as a value of bpf_token_path option and will force libbpf to
+	 * either create BPF token from provided custom BPF FS path, or will
+	 * disable implicit BPF token creation, if envvar value is an empty
+	 * string. bpf_token_path overrides LIBBPF_BPF_TOKEN_PATH, if both are
+	 * set at the same time.
+	 *
 	 * Setting bpf_token_path option to empty string disables libbpf's
 	 * automatic attempt to create BPF token from default BPF FS mount
 	 * point (/sys/fs/bpf), in case this default behavior is undesirable.
-- 
2.34.1