| 1 | //go:build !windows |
| 2 | |
| 3 | package agent |
| 4 | |
| 5 | import ( |
| 6 | "errors" |
| 7 | "os" |
| 8 | |
| 9 | "reasonix/internal/store" |
| 10 | |
| 11 | "golang.org/x/sys/unix" |
| 12 | ) |
| 13 | |
| 14 | // tryLockSessionFile attempts the compatibility save lock once without |
| 15 | // blocking. The shared wrapper in save.go supplies the bounded retry window. |
| 16 | func tryLockSessionFile(path string) (func(), error) { |
| 17 | f, err := os.OpenFile(store.SessionLockFile(path), os.O_CREATE|os.O_RDWR, 0o600) |
| 18 | if err != nil { |
| 19 | return nil, err |
| 20 | } |
| 21 | if err := unix.Flock(int(f.Fd()), unix.LOCK_EX|unix.LOCK_NB); err != nil { |
| 22 | _ = f.Close() |
| 23 | if errors.Is(err, unix.EWOULDBLOCK) || errors.Is(err, unix.EAGAIN) { |
| 24 | return nil, ErrSessionFileLockHeld |
| 25 | } |
| 26 | return nil, err |
| 27 | } |
| 28 | return func() { |
| 29 | _ = unix.Flock(int(f.Fd()), unix.LOCK_UN) |
| 30 | _ = f.Close() |
| 31 | }, nil |
| 32 | } |
| 33 | |
| 34 | // sessionLockFile is a non-blocking exclusive lock on a lock file itself, |
| 35 | // used by cleanup paths that may need to delete the file they locked. |
| 36 | type sessionLockFile struct { |
| 37 | f *os.File |
| 38 | } |
| 39 | |
| 40 | // tryTakeSessionLockFile opens lockPath and takes its exclusive flock without |
| 41 | // blocking. A live holder surfaces as ErrSessionFileLockHeld. |
| 42 | func tryTakeSessionLockFile(lockPath string) (*sessionLockFile, error) { |
| 43 | f, err := os.OpenFile(lockPath, os.O_CREATE|os.O_RDWR, 0o600) |
| 44 | if err != nil { |
| 45 | return nil, err |
| 46 | } |
| 47 | if err := unix.Flock(int(f.Fd()), unix.LOCK_EX|unix.LOCK_NB); err != nil { |
| 48 | _ = f.Close() |
| 49 | if errors.Is(err, unix.EWOULDBLOCK) || errors.Is(err, unix.EAGAIN) { |
| 50 | return nil, ErrSessionFileLockHeld |
| 51 | } |
| 52 | return nil, err |
| 53 | } |
| 54 | return &sessionLockFile{f: f}, nil |
| 55 | } |
| 56 | |
| 57 | func tryTakeSessionLeaseLockFile(lockPath string) (*sessionLockFile, error) { |
| 58 | return tryTakeSessionLockFile(lockPath) |
| 59 | } |
| 60 | |
| 61 | func (l *sessionLockFile) Unlock() { |
| 62 | _ = unix.Flock(int(l.f.Fd()), unix.LOCK_UN) |
| 63 | _ = l.f.Close() |
| 64 | } |
| 65 | |
| 66 | // writeOwnerInfo replaces the lock file's contents with b through the held |
| 67 | // descriptor while the flock is still held. The lease publishes its owner |
| 68 | // identity directly inside .lease.lock, so the metadata dies with the lock |
| 69 | // file on RemoveAndUnlock instead of surviving as a stale sidecar. |
| 70 | func (l *sessionLockFile) writeOwnerInfo(b []byte) error { |
| 71 | if l == nil || l.f == nil { |
| 72 | return errors.New("lease lock not held") |
| 73 | } |
| 74 | if err := l.f.Truncate(0); err != nil { |
| 75 | return err |
| 76 | } |
| 77 | if _, err := l.f.WriteAt(sessionLeaseOwnerBytes(b), 0); err != nil { |
| 78 | return err |
| 79 | } |
| 80 | return l.f.Sync() |
| 81 | } |
| 82 | |
| 83 | // RemoveAndUnlock deletes the lock file atomically with the release: the |
| 84 | // unlink happens while the flock is still held, so a waiter blocked on this |
| 85 | // inode can never adopt a file that is about to disappear for everyone else. |
| 86 | func (l *sessionLockFile) RemoveAndUnlock() error { |
| 87 | removeErr := os.Remove(l.f.Name()) |
| 88 | l.Unlock() |
| 89 | if removeErr != nil && !os.IsNotExist(removeErr) { |
| 90 | return removeErr |
| 91 | } |
| 92 | return nil |
| 93 | } |
| 94 | |
| 95 | func tryLockSessionLeaseFile(path string) (func(), error) { |
| 96 | f, err := os.OpenFile(store.SessionLeaseLock(path), os.O_CREATE|os.O_RDWR, 0o600) |
| 97 | if err != nil { |
| 98 | return nil, err |
| 99 | } |
| 100 | if err := unix.Flock(int(f.Fd()), unix.LOCK_EX|unix.LOCK_NB); err != nil { |
| 101 | _ = f.Close() |
| 102 | if errors.Is(err, unix.EWOULDBLOCK) || errors.Is(err, unix.EAGAIN) { |
| 103 | return nil, ErrSessionLeaseHeld |
| 104 | } |
| 105 | return nil, err |
| 106 | } |
| 107 | return func() { |
| 108 | _ = unix.Flock(int(f.Fd()), unix.LOCK_UN) |
| 109 | _ = f.Close() |
| 110 | }, nil |
| 111 | } |
| 112 | |
| 113 | func readSessionLeaseLockFile(path string) ([]byte, error) { |
| 114 | return os.ReadFile(path) |
| 115 | } |
| 116 |