[RFC PATCH bpf-next v2 2/6] libbpf: Add support for extended bpf syscall

[Leon Hwang <leon.hwang@linux.dev>]

To support the extended 'bpf()' syscall introduced in the previous commit,
this patch adds the following APIs:

1. *Internal:*

   * 'sys_bpf_extended()'
   * 'sys_bpf_fd_extended()'
     These wrap the raw 'syscall()' interface to support passing extended
     attributes.

2. *Exported:*

   * 'probe_sys_bpf_extended()'
     This function checks whether the running kernel supports the extended
     'bpf()' syscall with common attributes.

Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
---
 tools/lib/bpf/bpf.c             | 45 +++++++++++++++++++++++++++++++++
 tools/lib/bpf/bpf.h             |  1 +
 tools/lib/bpf/features.c        |  8 ++++++
 tools/lib/bpf/libbpf.map        |  2 ++
 tools/lib/bpf/libbpf_internal.h |  2 ++
 5 files changed, 58 insertions(+)

diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index ab40dbf9f020f..27845e287dd5c 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -69,6 +69,51 @@ static inline __u64 ptr_to_u64(const void *ptr)
 	return (__u64) (unsigned long) ptr;
 }
 
+static inline int sys_bpf_extended(enum bpf_cmd cmd, union bpf_attr *attr,
+				   unsigned int size,
+				   struct bpf_common_attr *common_attrs,
+				   unsigned int size_common)
+{
+	cmd = common_attrs ? cmd | BPF_COMMON_ATTRS : cmd & ~BPF_COMMON_ATTRS;
+	return syscall(__NR_bpf, cmd, attr, size, common_attrs, size_common);
+}
+
+static inline int sys_bpf_fd_extended(enum bpf_cmd cmd, union bpf_attr *attr,
+				      unsigned int size,
+				      struct bpf_common_attr *common_attrs,
+				      unsigned int size_common)
+{
+	int fd;
+
+	fd = sys_bpf_extended(cmd, attr, size, common_attrs, size_common);
+	return ensure_good_fd(fd);
+}
+
+int probe_sys_bpf_extended(int token_fd)
+{
+	const size_t attr_sz = offsetofend(union bpf_attr, prog_token_fd);
+	struct bpf_common_attr common_attrs;
+	struct bpf_insn insns[] = {
+		BPF_MOV64_IMM(BPF_REG_0, 0),
+		BPF_EXIT_INSN(),
+	};
+	union bpf_attr attr;
+
+	memset(&attr, 0, attr_sz);
+	attr.prog_type = BPF_PROG_TYPE_SOCKET_FILTER;
+	attr.license = ptr_to_u64("GPL");
+	attr.insns = ptr_to_u64(insns);
+	attr.insn_cnt = (__u32)ARRAY_SIZE(insns);
+	attr.prog_token_fd = token_fd;
+	if (token_fd)
+		attr.prog_flags |= BPF_F_TOKEN_FD;
+	libbpf_strlcpy(attr.prog_name, "libbpf_sysbpftest", sizeof(attr.prog_name));
+	memset(&common_attrs, 0, sizeof(common_attrs));
+
+	return sys_bpf_fd_extended(BPF_PROG_LOAD, &attr, attr_sz, &common_attrs,
+				   sizeof(common_attrs));
+}
+
 static inline int sys_bpf(enum bpf_cmd cmd, union bpf_attr *attr,
 			  unsigned int size)
 {
diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
index 7252150e7ad35..38819071ecbe7 100644
--- a/tools/lib/bpf/bpf.h
+++ b/tools/lib/bpf/bpf.h
@@ -35,6 +35,7 @@
 extern "C" {
 #endif
 
+LIBBPF_API int probe_sys_bpf_extended(int token_fd);
 LIBBPF_API int libbpf_set_memlock_rlim(size_t memlock_bytes);
 
 struct bpf_map_create_opts {
diff --git a/tools/lib/bpf/features.c b/tools/lib/bpf/features.c
index 760657f5224c2..a63172c6343d0 100644
--- a/tools/lib/bpf/features.c
+++ b/tools/lib/bpf/features.c
@@ -507,6 +507,11 @@ static int probe_kern_arg_ctx_tag(int token_fd)
 	return probe_fd(prog_fd);
 }
 
+static int probe_kern_extended_syscall(int token_fd)
+{
+	return probe_fd(probe_sys_bpf_extended(token_fd));
+}
+
 typedef int (*feature_probe_fn)(int /* token_fd */);
 
 static struct kern_feature_cache feature_cache;
@@ -582,6 +587,9 @@ static struct kern_feature_desc {
 	[FEAT_BTF_QMARK_DATASEC] = {
 		"BTF DATASEC names starting from '?'", probe_kern_btf_qmark_datasec,
 	},
+	[FEAT_EXTENDED_SYSCALL] = {
+		"Kernel supports extended syscall", probe_kern_extended_syscall,
+	},
 };
 
 bool feat_supported(struct kern_feature_cache *cache, enum kern_feature_id feat_id)
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index d7bd463e7017e..83d3d1af5ed1e 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -448,4 +448,6 @@ LIBBPF_1.6.0 {
 } LIBBPF_1.5.0;
 
 LIBBPF_1.7.0 {
+	global:
+		probe_sys_bpf_extended;
 } LIBBPF_1.6.0;
diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
index 477a3b3389a09..497d845339a6b 100644
--- a/tools/lib/bpf/libbpf_internal.h
+++ b/tools/lib/bpf/libbpf_internal.h
@@ -380,6 +380,8 @@ enum kern_feature_id {
 	FEAT_ARG_CTX_TAG,
 	/* Kernel supports '?' at the front of datasec names */
 	FEAT_BTF_QMARK_DATASEC,
+	/* Kernel supports extended syscall */
+	FEAT_EXTENDED_SYSCALL,
 	__FEAT_CNT,
 };
 
-- 
2.50.1