From 660e6a384d8c7b32a8486a0aeb31f75939a99b75 Mon Sep 17 00:00:00 2001
From: Rob Landley <rob@landley.net>
Date: Thu, 22 Oct 2020 19:48:15 -0500
Subject: Add nommu-able xvdaemon() and use it to remove some TOYBOX_FORK
 dependencies

---
 lib/lib.h             |  3 ++-
 lib/xwrap.c           | 24 ++++++++++++++++++++++++
 toys/net/sntp.c       |  5 ++---
 toys/other/watchdog.c |  3 +--
 4 files changed, 29 insertions(+), 6 deletions(-)

diff --git a/lib/lib.h b/lib/lib.h
index 6851c4aa..192fb7d2 100644
--- a/lib/lib.h
+++ b/lib/lib.h
@@ -127,12 +127,13 @@ char *xstrndup(char *s, size_t n);
 char *xstrdup(char *s);
 void *xmemdup(void *s, long len);
 char *xmprintf(char *format, ...) printf_format;
+void xflush(int flush);
 void xprintf(char *format, ...) printf_format;
 void xputsl(char *s, int len);
 void xputsn(char *s);
 void xputs(char *s);
 void xputc(char c);
-void xflush(int flush);
+void xvdaemon(void);
 void xexec(char **argv);
 pid_t xpopen_setup(char **argv, int *pipes, void (*callback)(char **argv));
 pid_t xpopen_both(char **argv, int *pipes);
diff --git a/lib/xwrap.c b/lib/xwrap.c
index cf7fc42a..85fa2405 100644
--- a/lib/xwrap.c
+++ b/lib/xwrap.c
@@ -182,6 +182,30 @@ void xputc(char c)
   xflush(0);
 }
 
+// daemonize via vfork(). Does not chdir("/"), caller should do that first
+// note: restarts process from command_main()
+void xvdaemon(void)
+{
+  int fd;
+
+  // vfork and exec /proc/self/exe
+  if (toys.stacktop) {
+    xpopen(0, 0, 0);
+    _exit(0);
+  }
+
+  // new session id, point fd 0-2 at /dev/null, detach from tty
+  setsid();
+  close(0);
+  xopen_stdio("/dev/null", O_RDWR);
+  dup2(0, 1);
+  if (-1 != (fd = open("/dev/tty", O_RDONLY))) {
+    ioctl(fd, TIOCNOTTY);
+    close(fd);
+  }
+  dup2(0, 2);
+}
+
 // This is called through the XVFORK macro because parent/child of vfork
 // share a stack, so child returning from a function would stomp the return
 // address parent would need. Solution: make vfork() an argument so processes
diff --git a/toys/net/sntp.c b/toys/net/sntp.c
index dae19485..161cab46 100644
--- a/toys/net/sntp.c
+++ b/toys/net/sntp.c
@@ -11,7 +11,6 @@ USE_SNTP(NEWTOY(sntp, ">1M :m :Sp:t#<0=1>16asdDqr#<4>17=10[!as]", TOYFLAG_USR|TO
 config SNTP
   bool "sntp"
   default y
-  depends on TOYBOX_FORK
   help
     usage: sntp [-saSdDq] [-r SHIFT] [-mM[ADDRESS]] [-p PORT] [SERVER]
 
@@ -79,6 +78,8 @@ void sntp_main(void)
   union socksaddr sa;
   int fd, tries = 0;
 
+  if (FLAG(d)) xvdaemon();
+
   if (FLAG(M)) toys.optflags |= FLAG_S;
   if (!(FLAG(S)||FLAG(m)) && !*toys.optargs)
     error_exit("Need -SMm or SERVER address");
@@ -88,8 +89,6 @@ void sntp_main(void)
   ai = xgetaddrinfo(*toys.optargs, TT.p, AF_UNSPEC, SOCK_DGRAM, IPPROTO_UDP,
     AI_PASSIVE*!*toys.optargs);
 
-  if (FLAG(d) && daemon(0, 0)) perror_exit("daemonize");
-
   // Act as server if necessary
   if (FLAG(S)||FLAG(m)) {
     fd = xbindany(ai);
diff --git a/toys/other/watchdog.c b/toys/other/watchdog.c
index a2e4fa01..232d82c0 100644
--- a/toys/other/watchdog.c
+++ b/toys/other/watchdog.c
@@ -9,7 +9,6 @@ USE_WATCHDOG(NEWTOY(watchdog, "<1>1Ft#=4<1T#=60<1", TOYFLAG_NEEDROOT|TOYFLAG_BIN
 config WATCHDOG
   bool "watchdog"
   default y
-  depends on TOYBOX_FORK
   help
     usage: watchdog [-F] [-t UPDATE] [-T DEADLINE] DEV
 
@@ -38,7 +37,7 @@ void safe_shutdown(int ignored) {
 
 void watchdog_main(void)
 {
-  if (!FLAG(F) && daemon(1, 1)) perror_exit("failed to daemonize");
+  if (!FLAG(F)) xvdaemon();
   xsignal(SIGTERM, safe_shutdown);
   xsignal(SIGINT, safe_shutdown);
   xioctl(TT.fd = xopen(*toys.optargs, O_WRONLY), WDIOC_SETTIMEOUT, &TT.T);
-- 
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