[RFC PATCH bpf-next v3 02/10] libbpf: Add support for extended bpf syscall

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

To support the extended 'bpf()' syscall introduced in the previous commit,
introduce the following internal APIs:

* 'sys_bpf_ext()'
* 'sys_bpf_ext_fd()'
  They wrap the raw 'syscall()' interface to support passing extended
  attributes.
* 'probe_sys_bpf_ext()'
  Check whether current kernel supports the extended attributes.

Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
---
 tools/lib/bpf/bpf.c             | 33 +++++++++++++++++++++++++++++++++
 tools/lib/bpf/features.c        |  8 ++++++++
 tools/lib/bpf/libbpf_internal.h |  3 +++
 3 files changed, 44 insertions(+)

diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index 339b197972374..9cd79beb13a2d 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -69,6 +69,39 @@ static inline __u64 ptr_to_u64(const void *ptr)
 	return (__u64) (unsigned long) ptr;
 }
 
+static inline int sys_bpf_ext(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_ext_fd(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_ext(cmd, attr, size, common_attrs, size_common);
+	return ensure_good_fd(fd);
+}
+
+int probe_sys_bpf_ext(void)
+{
+	const size_t attr_sz = offsetofend(union bpf_attr, prog_token_fd);
+	union bpf_attr attr;
+	int fd;
+
+	memset(&attr, 0, attr_sz);
+	fd = syscall(__NR_bpf, BPF_PROG_LOAD | BPF_COMMON_ATTRS, &attr, attr_sz, NULL,
+		     sizeof(struct bpf_common_attr));
+	fd = errno == EFAULT ? syscall(__NR_memfd_create, "fd", 0) : fd;
+	return ensure_good_fd(fd);
+}
+
 static inline int sys_bpf(enum bpf_cmd cmd, union bpf_attr *attr,
 			  unsigned int size)
 {
diff --git a/tools/lib/bpf/features.c b/tools/lib/bpf/features.c
index 760657f5224c2..d01df62394f89 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_ext());
+}
+
 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_internal.h b/tools/lib/bpf/libbpf_internal.h
index c93797dcaf5bc..af05df8d040ce 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,
 };
 
@@ -740,4 +742,5 @@ int probe_fd(int fd);
 #define SHA256_DWORD_SIZE SHA256_DIGEST_LENGTH / sizeof(__u64)
 
 void libbpf_sha256(const void *data, size_t len, __u8 out[SHA256_DIGEST_LENGTH]);
+int probe_sys_bpf_ext(void);
 #endif /* __LIBBPF_LIBBPF_INTERNAL_H */
-- 
2.51.0