chore(prog): align BPFProg API (#467)

Align BPFProg API to return error accordingly:

- SetType() -> bpf_program__set_type() 
- SetExpectedAttachType() -> bpf_program__set_expected_attach_type()

Both SetProgramType() and SetAttachType() are now deprecated.

prog.go

@@ -155,14 +155,32 @@ func (p *BPFProg) SetAttachTarget(attachProgFD int, attachFuncName string) error
 	return nil
 }
 
-// TODO: fix API to return error
+// Deprecated: use BPFProg.SetType() instead.
 func (p *BPFProg) SetProgramType(progType BPFProgType) {
-	C.bpf_program__set_type(p.prog, C.enum_bpf_prog_type(int(progType)))
+	_ = p.SetType(progType)
 }
 
-// TODO: fix API to return error
+func (p *BPFProg) SetType(progType BPFProgType) error {
+	retC := C.bpf_program__set_type(p.prog, C.enum_bpf_prog_type(progType))
+	if retC < 0 {
+		return fmt.Errorf("failed to set prog_type %s for program %s: %w", progType.String(), p.Name(), syscall.Errno(-retC))
+	}
+
+	return nil
+}
+
+// Deprecated: use BPFProg.SetExpectedAttachType() instead.
 func (p *BPFProg) SetAttachType(attachType BPFAttachType) {
-	C.bpf_program__set_expected_attach_type(p.prog, C.enum_bpf_attach_type(int(attachType)))
+	_ = p.SetExpectedAttachType(attachType)
+}
+
+func (p *BPFProg) SetExpectedAttachType(attachType BPFAttachType) error {
+	retC := C.bpf_program__set_expected_attach_type(p.prog, C.enum_bpf_attach_type(attachType))
+	if retC < 0 {
+		return fmt.Errorf("failed to set attach_type %s for program %s: %w", attachType.String(), p.Name(), syscall.Errno(-retC))
+	}
+
+	return nil
 }
 
 // getCgroupDirFD returns a file descriptor for a given cgroup2 directory path

selftest/set-attach/main.go

@@ -30,8 +30,16 @@ func main() {
 
 	// eBPF program type should only be set if it differs from the desired one
 	// commit d6e6286a12e7 ("libbpf: disassociate section handler on explicit bpf_program__set_type() call")
-	// prog.SetProgramType(bpf.BPFProgTypeTracing)
-	prog.SetAttachType(bpf.BPFAttachTypeTraceFentry)
+	// err = prog.SetType(bpf.BPFProgTypeTracing)
+	// if err != nil {
+	//	 fmt.Fprintln(os.Stderr, err)
+	//	 os.Exit(-1)
+	// }
+	err = prog.SetExpectedAttachType(bpf.BPFAttachTypeTraceFentry)
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(-1)
+	}
 
 	funcName := fmt.Sprintf("__%s_sys_mmap", ksymArch())
 	err = prog.SetAttachTarget(0, funcName)