chore(prog): Add attach/detach legacy api for xdp (#438)

The AttachXDP api use bpf link to attach xdp prog, AttachXDPLegacy/DetachXDPLegacy
apis corresponds to bpf_xdp_attach/bpf_xdp_detach, which can be used on
old kernel, so add it.

Signed-off-by: Tao Chen <[email protected]>

libbpfgo.c

@@ -536,3 +536,21 @@ __u32 cgo_bpf_tc_opts_priority(struct bpf_tc_opts *opts)
 
     return opts->priority;
 }
+
+struct bpf_xdp_attach_opts *cgo_bpf_xdp_attach_opts_new(__u32 fd)
+{
+    struct bpf_xdp_attach_opts *opts;
+    opts = calloc(1, sizeof(*opts));
+
+    if (!opts)
+        return NULL;
+    opts->sz = sizeof(*opts);
+    opts->old_prog_fd = fd;
+
+    return opts;
+}
+
+void cgo_bpf_xdp_attach_opts_free(struct bpf_xdp_attach_opts *opts)
+{
+    free(opts);
+}

libbpfgo.h

@@ -16,7 +16,8 @@
 
 #include <bpf/bpf.h>
 #include <bpf/libbpf.h>
-#include <linux/bpf.h> // uapi
+#include <linux/bpf.h>     // uapi
+#include <linux/if_link.h> // uapi
 
 void cgo_libbpf_set_print_fn();
 
@@ -122,4 +123,9 @@ __u32 cgo_bpf_tc_opts_prog_id(struct bpf_tc_opts *opts);
 __u32 cgo_bpf_tc_opts_handle(struct bpf_tc_opts *opts);
 __u32 cgo_bpf_tc_opts_priority(struct bpf_tc_opts *opts);
 
+// bpf_xdp_attach_opts
+
+struct bpf_xdp_attach_opts *cgo_bpf_xdp_attach_opts_new(__u32 fd);
+void cgo_bpf_xdp_attach_opts_free(struct bpf_xdp_attach_opts *opts);
+
 #endif

prog-common.go

@@ -237,3 +237,19 @@ const (
 	BPFFAllowMulti    AttachFlag = C.BPF_F_ALLOW_MULTI
 	BPFFReplace       AttachFlag = C.BPF_F_REPLACE
 )
+
+//
+// XDPFlags
+//
+
+type XDPFlags uint32
+
+const (
+	XDPFlagsUpdateIfNoExist XDPFlags = C.XDP_FLAGS_UPDATE_IF_NOEXIST
+	XDPFlagsSkbMode         XDPFlags = C.XDP_FLAGS_SKB_MODE
+	XDPFlagsDrvMode         XDPFlags = C.XDP_FLAGS_DRV_MODE
+	XDPFlagsHwMode          XDPFlags = C.XDP_FLAGS_HW_MODE
+	XDPFlagsReplace         XDPFlags = C.XDP_FLAGS_REPLACE
+	XDPFlagsModes           XDPFlags = C.XDP_FLAGS_MODES
+	XDPFlagsMask            XDPFlags = C.XDP_FLAGS_MASK
+)

prog.go

@@ -309,6 +309,44 @@ func (p *BPFProg) AttachXDP(deviceName string) (*BPFLink, error) {
 	return bpfLink, nil
 }
 
+func (p *BPFProg) AttachXDPLegacy(deviceName string, flag XDPFlags) error {
+	optsC, errno := C.cgo_bpf_xdp_attach_opts_new(C.uint32_t(0))
+	if optsC == nil {
+		return fmt.Errorf("failed to create xdp attach opts:%w", errno)
+	}
+	defer C.cgo_bpf_xdp_attach_opts_free(optsC)
+	iface, err := net.InterfaceByName(deviceName)
+	if err != nil {
+		return fmt.Errorf("failed to find device by name %s: %w", deviceName, err)
+	}
+	var retC C.int
+	retC, errno = C.bpf_xdp_attach(C.int(iface.Index), C.int(p.FileDescriptor()), C.uint32_t(flag), optsC)
+	if retC < 0 {
+		return fmt.Errorf("failed to attach xdp: %w", errno)
+	}
+
+	return nil
+}
+
+func (p *BPFProg) DetachXDPLegacy(deviceName string, flag XDPFlags) error {
+	optsC, errno := C.cgo_bpf_xdp_attach_opts_new(C.uint32_t(p.FileDescriptor()))
+	if optsC == nil {
+		return fmt.Errorf("failed to create xdp attach opts:%w", errno)
+	}
+	defer C.cgo_bpf_xdp_attach_opts_free(optsC)
+	iface, err := net.InterfaceByName(deviceName)
+	if err != nil {
+		return fmt.Errorf("failed to find device by name %s: %w", deviceName, err)
+	}
+	var retC C.int
+	retC, errno = C.bpf_xdp_detach(C.int(iface.Index), C.uint32_t(flag), optsC)
+	if retC < 0 {
+		return fmt.Errorf("failed to detach xdp: %w", errno)
+	}
+
+	return nil
+}
+
 func (p *BPFProg) AttachTracepoint(category, name string) (*BPFLink, error) {
 	tpCategoryC := C.CString(category)
 	defer C.free(unsafe.Pointer(tpCategoryC))

selftest/xdp/main.go

@@ -35,6 +35,17 @@ func main() {
 		os.Exit(-1)
 	}
 
+	err = xdpProg.AttachXDPLegacy(deviceName, bpf.XDPFlagsReplace)
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(-1)
+	}
+	err = xdpProg.DetachXDPLegacy(deviceName, bpf.XDPFlagsReplace)
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(-1)
+	}
+
 	_, err = xdpProg.AttachXDP(deviceName)
 	if err != nil {
 		fmt.Fprintln(os.Stderr, err)