BPFProg: create AttachCgroup to allow Cgroup link attachments

Create AttachCgroup(string) to allow the following program types:

- BPF_PROG_TYPE_CGROUP_SKB
- BPF_PROG_TYPE_CGROUP_SOCK
- BPF_PROG_TYPE_CGROUP_DEVICE
- BPF_PROG_TYPE_CGROUP_SOCK_ADDR
- BPF_PROG_TYPE_CGROUP_SYSCTL
- BPF_PROG_TYPE_CGROUP_SOCKOPT

to be attached to a cgroupv2 directory file descriptor, such as:

- /sys/fs/cgroup/unified
- /sys/fs/cgroup/unified/user.slice/user-1000.slice

and on...

Those eBPF program types will be triggered for all processes within the
cgroupv2 they were attached to.

libbpfgo.go

@@ -93,6 +93,7 @@ import (
  "fmt"
  "net"
  "path/filepath"
+ "strings"
  "sync"
  "syscall"
  "unsafe"
@@ -237,6 +238,7 @@ const (
  Uretprobe
  Tracing
  XDP
+ Cgroup
 )
 
 type BPFLink struct {
@@ -1302,6 +1304,36 @@ func (p *BPFProg) SetAttachType(attachType BPFAttachType) {
  C.bpf_program__set_expected_attach_type(p.prog, C.enum_bpf_attach_type(int(attachType)))
 }
 
+func (p *BPFProg) AttachCgroup(cgroupV2DirPath string) (*BPFLink, error) {
+ const (
+ O_DIRECTORY int = 0200000
+ O_RDONLY int = 00
+ )
+ fd, err := syscall.Open(cgroupV2DirPath, O_DIRECTORY|O_RDONLY, 0)
+ if fd < 0 {
+ return nil, fmt.Errorf("failed to open cgroupv2 directory path %s: %w", cgroupV2DirPath, err)
+ }
+ link := C.bpf_program__attach_cgroup(p.prog, C.int(fd))
+ if C.IS_ERR_OR_NULL(unsafe.Pointer(link)) {
+ return nil, errptrError(unsafe.Pointer(link), "failed to attach cgroup on cgroupv2 %s to program %s", cgroupV2DirPath, p.name)
+ }
+
+ // dirName will be used in bpfLink.eventName. eventName follows a format
+ // convention and is used to better identify link types and what they are
+ // linked with in case of errors or similar needs. Having eventName as:
+ // cgroup-progName-/sys/fs/cgroup/unified/ would look weird so replace it
+ // to be cgroup-progName-sys-fs-cgroup-unified instead.
+ dirName := strings.ReplaceAll(cgroupV2DirPath[1:], "/", "-")
+ bpfLink := &BPFLink{
+ link: link,
+ prog: p,
+ linkType: Cgroup,
+ eventName: fmt.Sprintf("cgroup-%s-%s", p.name, dirName),
+ }
+ p.module.links = append(p.module.links, bpfLink)
+ return bpfLink, nil
+}
+
 func (p *BPFProg) AttachXDP(deviceName string) (*BPFLink, error) {
  iface, err := net.InterfaceByName(deviceName)
  if err != nil {