Avoid left over dot lock file after reboot

---
 dotlock.c |   50 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 50 insertions(+)

--- dotlock.c
+++ dotlock.c	2020-02-17 11:16:22.785018224 +0000
@@ -30,8 +30,38 @@
 #define O_SYNC	0
 #endif
 
+#if defined(__linux__)
+#  include <sys/statfs.h>
+#  include <unistd.h>
+#  ifndef  TMPFS_MAGIC
+#    define TMPFS_MAGIC 0x01021994
+#  endif
+#endif
+
 #include "dotlock.h"
 
+#if defined(__linux__)
+static char *sys_tmpdir;
+static int
+dosys_tmpdir ()
+{
+	static char *shm = "/dev/shm";
+	struct statfs fs;
+	static int doshm;
+
+	if (doshm)
+		return (sys_tmpdir != NULL);
+
+	doshm++;
+
+	if (statfs(shm, &fs) < 0 || fs.f_type != TMPFS_MAGIC || eaccess(shm, W_OK|X_OK))
+		return 0;
+
+	sys_tmpdir = shm;
+	return 1;
+}
+#endif
+
 static int create_exclusive(const char *);
 /*
  * Create a unique file. O_EXCL does not really work over NFS so we follow
@@ -140,7 +170,17 @@ dot_lock(const char *fname, int pollinte
 	(void)sigaddset(&nset, SIGTSTP);
 	(void)sigaddset(&nset, SIGCHLD);
 
+#if defined(__linux__)
+	const char *ptr;
+	if ((ptr = strrchr(fname, '/')) && dosys_tmpdir()) {
+		ptr++;
+		fname = ptr;
+		(void)snprintf(path, sizeof(path), "%s/%s.lock", sys_tmpdir, fname);
+	} else
+		(void)snprintf(path, sizeof(path), "%s.lock", fname);
+#else
 	(void)snprintf(path, sizeof(path), "%s.lock", fname);
+#endif
 
 	retval = -1;
 	for (;;) {
@@ -174,6 +214,16 @@ dot_unlock(const char *fname)
 {
 	char path[MAXPATHLEN];
 
+#if defined(__linux__)
+	const char *ptr;
+	if ((ptr = strrchr(fname, '/')) && dosys_tmpdir()) {
+		ptr++;
+		fname = ptr;
+		(void)snprintf(path, sizeof(path), "%s/%s.lock", sys_tmpdir, fname);
+	} else
+		(void)snprintf(path, sizeof(path), "%s.lock", fname);
+#else
 	(void)snprintf(path, sizeof(path), "%s.lock", fname);
+#endif
 	(void)unlink(path);
 }