libbpf: Add support for extended BPF syscall

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 BPF syscall common attributes.

Acked-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
Link: https://lore.kernel.org/r/20260512153157.28382-3-leon.hwang@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index 5846de3642090a20bc6c6d75e49b454c4b29c609..9d8740761b7a86b191c6bb59445b4fcc3eafe81a 100644 (file)
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -69,6 +69,42 @@ 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 *attr_common,
+                             unsigned int size_common)
+{
+       cmd = attr_common ? (cmd | BPF_COMMON_ATTRS) : (cmd & ~BPF_COMMON_ATTRS);
+       return syscall(__NR_bpf, cmd, attr, size, attr_common, size_common);
+}
+
+static inline int sys_bpf_ext_fd(enum bpf_cmd cmd, union bpf_attr *attr,
+                                unsigned int size,
+                                struct bpf_common_attr *attr_common,
+                                unsigned int size_common)
+{
+       int fd;
+
+       fd = sys_bpf_ext(cmd, attr, size, attr_common, 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));
+       if (fd >= 0) {
+               close(fd);
+               return -EINVAL;
+       }
+       return errno == EFAULT ? 1 : 0;
+}
+
 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 4f19a0d79b0cfa6bbe0bebe09292c5944f2ce25d..b7e388f99d0bbd0e97755cf2d3221867ac812882 100644 (file)
--- a/tools/lib/bpf/features.c
+++ b/tools/lib/bpf/features.c
@@ -615,6 +615,11 @@ static int probe_kern_btf_layout(int token_fd)
                                                 (char *)layout, token_fd));
 }
 
+static int probe_bpf_syscall_common_attrs(int token_fd)
+{
+       return probe_sys_bpf_ext();
+}
+
 typedef int (*feature_probe_fn)(int /* token_fd */);
 
 static struct kern_feature_cache feature_cache;
@@ -699,6 +704,9 @@ static struct kern_feature_desc {
        [FEAT_BTF_LAYOUT] = {
                "kernel supports BTF layout", probe_kern_btf_layout,
        },
+       [FEAT_BPF_SYSCALL_COMMON_ATTRS] = {
+               "BPF syscall common attributes support", probe_bpf_syscall_common_attrs,
+       },
 };
 
 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 3781c45b46d3bfcd372ecc8bcc47447f26742730..7d93c6c01d6029dcc940a005c576dc5010880459 100644 (file)
--- a/tools/lib/bpf/libbpf_internal.h
+++ b/tools/lib/bpf/libbpf_internal.h
@@ -398,6 +398,8 @@ enum kern_feature_id {
        FEAT_UPROBE_SYSCALL,
        /* Kernel supports BTF layout information */
        FEAT_BTF_LAYOUT,
+       /* Kernel supports BPF syscall common attributes */
+       FEAT_BPF_SYSCALL_COMMON_ATTRS,
        __FEAT_CNT,
 };
 
@@ -768,4 +770,5 @@ 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 */