| 1 | //go:build unix |
| 2 | |
| 3 | package hostexec |
| 4 | |
| 5 | import ( |
| 6 | "errors" |
| 7 | |
| 8 | "golang.org/x/sys/unix" |
| 9 | ) |
| 10 | |
| 11 | // Observers, including root and adopt, never create or repair an agent's |
| 12 | // lifetime locks. Missing locks deny admission without changing the namespace. |
| 13 | func probeLifetime(dir, host string) (func(), error) { return probeExisting(dir, host, ".lock") } |
| 14 | func probeLive(dir, host string) (func(), error) { return probeExisting(dir, host, ".live") } |
| 15 | func probeExisting(dir, host, suffix string) (func(), error) { |
| 16 | if _, err := Key(host, "check"); err != nil { |
| 17 | return nil, err |
| 18 | } |
| 19 | fd, err := openDir(dir) |
| 20 | if err != nil { |
| 21 | return nil, err |
| 22 | } |
| 23 | defer unix.Close(fd) |
| 24 | lock, err := unix.Openat(fd, host+suffix, unix.O_RDONLY|unix.O_NOFOLLOW|unix.O_CLOEXEC|unix.O_NONBLOCK, 0) |
| 25 | if err != nil { |
| 26 | return nil, err |
| 27 | } |
| 28 | fail := func(err error) (func(), error) { _ = unix.Close(lock); return nil, err } |
| 29 | var st unix.Stat_t |
| 30 | if err = unix.Fstat(lock, &st); err != nil { |
| 31 | return fail(err) |
| 32 | } |
| 33 | if st.Mode&unix.S_IFMT != unix.S_IFREG || st.Nlink != 1 { |
| 34 | return fail(ErrState) |
| 35 | } |
| 36 | if err = unix.Flock(lock, unix.LOCK_EX|unix.LOCK_NB); err == nil { |
| 37 | return func() { _ = unix.Flock(lock, unix.LOCK_UN); _ = unix.Close(lock) }, nil |
| 38 | } |
| 39 | if errors.Is(err, unix.EWOULDBLOCK) || errors.Is(err, unix.EAGAIN) { |
| 40 | return fail(ErrControllerBusy) |
| 41 | } |
| 42 | return fail(err) |
| 43 | } |
| 44 | |
amadan