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package link
import (
"fmt"
"unsafe"
"github.com/cilium/ebpf"
"github.com/cilium/ebpf/internal"
)
var ErrNotSupported = internal.ErrNotSupported
// Link represents a Program attached to a BPF hook.
type Link interface {
// Replace the current program with a new program.
//
// Passing a nil program is an error. May return an error wrapping ErrNotSupported.
Update(*ebpf.Program) error
// Persist a link by pinning it into a bpffs.
//
// May return an error wrapping ErrNotSupported.
Pin(string) error
// Close frees resources.
//
// The link will be broken unless it has been pinned. A link
// may continue past the lifetime of the process if Close is
// not called.
Close() error
// Prevent external users from implementing this interface.
isLink()
}
// ID uniquely identifies a BPF link.
type ID uint32
// RawLinkOptions control the creation of a raw link.
type RawLinkOptions struct {
// File descriptor to attach to. This differs for each attach type.
Target int
// Program to attach.
Program *ebpf.Program
// Attach must match the attach type of Program.
Attach ebpf.AttachType
}
// RawLinkInfo contains metadata on a link.
type RawLinkInfo struct {
Type Type
ID ID
Program ebpf.ProgramID
}
// RawLink is the low-level API to bpf_link.
//
// You should consider using the higher level interfaces in this
// package instead.
type RawLink struct {
fd *internal.FD
}
// AttachRawLink creates a raw link.
func AttachRawLink(opts RawLinkOptions) (*RawLink, error) {
if err := haveBPFLink(); err != nil {
return nil, err
}
if opts.Target < 0 {
return nil, fmt.Errorf("invalid target: %s", internal.ErrClosedFd)
}
progFd := opts.Program.FD()
if progFd < 0 {
return nil, fmt.Errorf("invalid program: %s", internal.ErrClosedFd)
}
attr := bpfLinkCreateAttr{
targetFd: uint32(opts.Target),
progFd: uint32(progFd),
attachType: opts.Attach,
}
fd, err := bpfLinkCreate(&attr)
if err != nil {
return nil, fmt.Errorf("can't create link: %s", err)
}
return &RawLink{fd}, nil
}
// LoadPinnedRawLink loads a persisted link from a bpffs.
func LoadPinnedRawLink(fileName string) (*RawLink, error) {
return loadPinnedRawLink(fileName, UnspecifiedType)
}
func loadPinnedRawLink(fileName string, typ Type) (*RawLink, error) {
fd, err := internal.BPFObjGet(fileName)
if err != nil {
return nil, fmt.Errorf("load pinned link: %s", err)
}
link := &RawLink{fd}
if typ == UnspecifiedType {
return link, nil
}
info, err := link.Info()
if err != nil {
link.Close()
return nil, fmt.Errorf("get pinned link info: %s", err)
}
if info.Type != typ {
link.Close()
return nil, fmt.Errorf("link type %v doesn't match %v", info.Type, typ)
}
return link, nil
}
func (l *RawLink) isLink() {}
// FD returns the raw file descriptor.
func (l *RawLink) FD() int {
fd, err := l.fd.Value()
if err != nil {
return -1
}
return int(fd)
}
// Close breaks the link.
//
// Use Pin if you want to make the link persistent.
func (l *RawLink) Close() error {
return l.fd.Close()
}
// Pin persists a link past the lifetime of the process.
//
// Calling Close on a pinned Link will not break the link
// until the pin is removed.
func (l *RawLink) Pin(fileName string) error {
if err := internal.BPFObjPin(fileName, l.fd); err != nil {
return fmt.Errorf("can't pin link: %s", err)
}
return nil
}
// Update implements Link.
func (l *RawLink) Update(new *ebpf.Program) error {
return l.UpdateArgs(RawLinkUpdateOptions{
New: new,
})
}
// RawLinkUpdateOptions control the behaviour of RawLink.UpdateArgs.
type RawLinkUpdateOptions struct {
New *ebpf.Program
Old *ebpf.Program
Flags uint32
}
// UpdateArgs updates a link based on args.
func (l *RawLink) UpdateArgs(opts RawLinkUpdateOptions) error {
newFd := opts.New.FD()
if newFd < 0 {
return fmt.Errorf("invalid program: %s", internal.ErrClosedFd)
}
var oldFd int
if opts.Old != nil {
oldFd = opts.Old.FD()
if oldFd < 0 {
return fmt.Errorf("invalid replacement program: %s", internal.ErrClosedFd)
}
}
linkFd, err := l.fd.Value()
if err != nil {
return fmt.Errorf("can't update link: %s", err)
}
attr := bpfLinkUpdateAttr{
linkFd: linkFd,
newProgFd: uint32(newFd),
oldProgFd: uint32(oldFd),
flags: opts.Flags,
}
return bpfLinkUpdate(&attr)
}
// struct bpf_link_info
type bpfLinkInfo struct {
typ uint32
id uint32
prog_id uint32
}
// Info returns metadata about the link.
func (l *RawLink) Info() (*RawLinkInfo, error) {
var info bpfLinkInfo
err := internal.BPFObjGetInfoByFD(l.fd, unsafe.Pointer(&info), unsafe.Sizeof(info))
if err != nil {
return nil, fmt.Errorf("link info: %s", err)
}
return &RawLinkInfo{
Type(info.typ),
ID(info.id),
ebpf.ProgramID(info.prog_id),
}, nil
}
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