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monitor.go
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monitor.go
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package embedshim
import (
"fmt"
"os"
"path/filepath"
"strconv"
"sync"
"syscall"
"github.com/fuweid/embedshim/pkg/exitsnoop"
"github.com/fuweid/embedshim/pkg/pidfd"
"github.com/cilium/ebpf"
"github.com/pkg/errors"
"golang.org/x/sys/unix"
)
var (
// unexpectedExitCode is used when failed to get correct exit code.
unexpectedExitCode = 128
)
type monitor struct {
sync.Mutex
pidPoller *pidfd.Epoller
initStore *exitsnoop.Store
execStore *exitsnoop.Store
}
func newMonitor(stateDir string) (_ *monitor, retErr error) {
epoller, err := pidfd.NewEpoller()
if err != nil {
return nil, err
}
defer func() {
if retErr != nil {
epoller.Close()
}
}()
initStore, err := exitsnoop.NewStore(stateDir)
if err != nil {
return nil, err
}
defer func() {
if retErr != nil {
initStore.Close()
}
}()
execStore, err := exitsnoop.NewStoreFromAttach()
if err != nil {
return nil, err
}
m := &monitor{
pidPoller: epoller,
initStore: initStore,
execStore: execStore,
}
// TODO: check the return
go m.pidPoller.Run()
return m, nil
}
// traceInitProcess checks init process is alive and starts to trace it's exit
// event by exitsnoop bpf tracepoint.
func (m *monitor) traceInitProcess(init *initProcess) (retErr error) {
m.Lock()
defer m.Unlock()
fd, err := pidfd.Open(uint32(init.Pid()), 0)
if err != nil {
return fmt.Errorf("failed to open pidfd for %s: %w", init, err)
}
defer func() {
if retErr != nil {
unix.Close(int(fd))
}
}()
// NOTE: The pid might be reused before pidfd.Open(like oom-killer or
// manually kill), so that we need to check the runc-init's exec.fifo
// file descriptor which is the "identity" of runc-init. :)
//
// Why we don't use runc-state commandline?
//
// The runc-state command only checks /proc/$pid/status's starttime,
// which is not reliable. And then it only checks exec.fifo exist in
// disk, but the runc-init has been killed. So we can't just use it.
if err := checkRuncInitAlive(init); err != nil {
return err
}
nsInfo, err := getPidnsInfo(uint32(init.Pid()))
if err != nil {
return fmt.Errorf("failed to get pidns info: %w", err)
}
if err := m.initStore.Trace(uint32(init.Pid()), &exitsnoop.TaskInfo{
TraceID: init.traceEventID,
PidnsInfo: nsInfo,
}); err != nil {
return fmt.Errorf("failed to insert taskinfo for %s: %w", init, err)
}
defer func() {
if retErr != nil {
m.initStore.DeleteTracingTask(uint32(init.Pid()))
m.initStore.DeleteExitedEvent(init.traceEventID)
}
}()
// Before trace it, the init-process might be killed and the exitsnoop
// tracepoint will not work, we need to check it alive again by pidfd.
if err := fd.SendSignal(0, 0); err != nil {
return err
}
if err := m.pidPoller.Add(fd, func() error {
// TODO(fuweid): do we need to check the pid value in event?
status, err := m.initStore.GetExitedEvent(init.traceEventID)
if err != nil {
init.SetExited(unexpectedExitCode)
return fmt.Errorf("failed to get exited status: %w", err)
}
init.SetExited(int(status.ExitCode))
return nil
}); err != nil {
return err
}
return nil
}
// repollingInitProcess is used to watch pidfd event after containerd restarts.
func (m *monitor) repollingInitProcess(init *initProcess) (retErr error) {
var (
eventID = init.traceEventID
exitedStatus *exitsnoop.ExitStatus
taskInfo *exitsnoop.TaskInfo
fd pidfd.FD
closeFD bool
err error
)
// fast path: check exit event from exitsnoop
exitedStatus, err = m.initStore.GetExitedEvent(eventID)
if err == nil {
init.SetExited(int(exitedStatus.ExitCode))
return nil
}
if !errors.Is(err, ebpf.ErrKeyNotExist) {
return err
}
fd, err = pidfd.Open(uint32(init.Pid()), 0)
if err != nil {
if !errors.Is(err, syscall.ESRCH) {
return err
}
goto set_exitedstatus
}
closeFD = true
defer func() {
if retErr != nil && closeFD {
unix.Close(int(fd))
}
}()
taskInfo, err = m.initStore.GetTracingTask(uint32(init.Pid()))
if err != nil {
if !errors.Is(err, ebpf.ErrKeyNotExist) {
return err
}
goto set_exitedstatus
}
// Just in case, the pid has been reused by other init process
if taskInfo != nil && taskInfo.TraceID == eventID {
return m.pidPoller.Add(fd, func() error {
// TODO(fuweid): do we need to check the pid value in event?
exitedStatus, err = m.initStore.GetExitedEvent(init.traceEventID)
if err != nil {
init.SetExited(unexpectedExitCode)
return fmt.Errorf("failed to get exited status: %w", err)
}
init.SetExited(int(exitedStatus.ExitCode))
return nil
})
}
unix.Close(int(fd))
closeFD = false
set_exitedstatus:
exitedStatus, err = m.initStore.GetExitedEvent(eventID)
if err != nil {
init.SetExited(unexpectedExitCode)
return err
}
init.SetExited(int(exitedStatus.ExitCode))
return nil
}
func getPidnsInfo(pid uint32) (exitsnoop.PidnsInfo, error) {
f, err := os.Stat(filepath.Join("/proc", strconv.Itoa(int(pid)), "ns", "pid"))
if err != nil {
return exitsnoop.PidnsInfo{}, err
}
return exitsnoop.PidnsInfo{
Dev: (f.Sys().(*syscall.Stat_t)).Dev,
Ino: (f.Sys().(*syscall.Stat_t)).Ino,
}, nil
}