bastion 0.53.2

client-go/singleton_linux.go

@@ -0,0 +1,37 @@
+//go:build linux
+
+package main
+
+import (
+	"os"
+	"syscall"
+
+	"golang.org/x/sys/unix"
+)
+
+// stdinIsTerminal distinguishes a person at a shell from the service. It decides
+// which way the machine lock waits: a human who typed `run` wants "already
+// running" immediately, while the unit must BLOCK so a restart queues behind the
+// dying primary instead of exiting and being restarted every two seconds — the
+// crash-loop the lock exists to end.
+//
+// It is a real isatty (TCGETS), not a character-device test. os.ModeCharDevice —
+// which the first draft used — is TRUE for /dev/null, and every installed daemon
+// has stdin on /dev/null: the installed unit sets no StandardInput, so systemd's
+// default (null) applies. The daemon therefore took the fail-fast branch in the
+// only deployment shape that exists, and the blocking standby the design asks
+// for was unreachable. Measured on 18 of 18 reachable boxes in one deployment.
+func stdinIsTerminal() bool {
+	_, err := unix.IoctlGetTermios(int(os.Stdin.Fd()), unix.TCGETS)
+	return err == nil
+}
+
+// ownerUID reports the owning uid of a stat result. Used to refuse locking inside
+// a runtime directory root does not own.
+func ownerUID(fi os.FileInfo) (uint32, bool) {
+	st, ok := fi.Sys().(*syscall.Stat_t)
+	if !ok {
+		return 0, false
+	}
+	return st.Uid, true
+}