From bd9faa81bff04df273d7b158a27cfe9765cacca4 Mon Sep 17 00:00:00 2001
From: Johnothan King <johnothanking@protonmail.com>
Date: Thu, 27 Jan 2022 22:58:01 -0800
Subject: [PATCH] libast: Use POSIX_SPAWN_SETSID in spawnveg when needed (#439)

This commit implements support for POSIX_SPAWN_SETSID in
spawnveg(3). The fork/vfork fallback for spawnveg already attempts
to use setsid in the manner described by the man page, so the
posix_spawn implementation should also do so.

src/lib/libast/comp/spawnveg.c:
- Add support for POSIX_SPAWN_SETSID to the posix_spawn version of
  spawnveg.
- Minor extra: Remove dead code that's never used (the
  _lib_posix_spawn < 2 code block is inside of _lib_posix_spawn >
  1, plus when it's manually enabled by changing the previous #if
  condition you'll find it causes many regression test failures (at
  least on OpenBSD)).

src/lib/libast/man/spawnveg.3:
- Document that spawnveg cannot make the new process a session
  leader if the operating system doesn't support POSIX_SPAWN_SETSID
  and the new process was created using posix_spawn.
---
 src/lib/libast/comp/spawnveg.c | 22 ++++++++++------------
 src/lib/libast/man/spawnveg.3  | 11 +++++++++--
 2 files changed, 19 insertions(+), 14 deletions(-)

diff --git a/src/lib/libast/comp/spawnveg.c b/src/lib/libast/comp/spawnveg.c
index bb0db2a8a..ee78d9960 100644
--- a/src/lib/libast/comp/spawnveg.c
+++ b/src/lib/libast/comp/spawnveg.c
@@ -47,20 +47,27 @@ NoN(spawnveg)
 pid_t
 spawnveg(const char* path, char* const argv[], char* const envv[], pid_t pgid)
 {
-	int			err;
+	int			err, flags = 0;
 	pid_t			pid;
 	posix_spawnattr_t	attr;
 
 	if (err = posix_spawnattr_init(&attr))
 		goto nope;
+#if POSIX_SPAWN_SETSID
+	if (pgid == -1)
+		flags |= POSIX_SPAWN_SETSID;
+	else
+#endif
 	if (pgid)
+		flags |= POSIX_SPAWN_SETPGROUP;
+	if (flags && (err = posix_spawnattr_setflags(&attr, flags)))
+		goto bad;
+	if (pgid && pgid != -1)
 	{
 		if (pgid <= 1)
 			pgid = 0;
 		if (err = posix_spawnattr_setpgroup(&attr, pgid))
 			goto bad;
-		if (err = posix_spawnattr_setflags(&attr, POSIX_SPAWN_SETPGROUP))
-			goto bad;
 	}
 	if (err = posix_spawn(&pid, path, NiL, &attr, argv, envv ? envv : environ))
 	{
@@ -68,15 +75,6 @@ spawnveg(const char* path, char* const argv[], char* const envv[], pid_t pgid)
 			goto bad;
 	}
 	posix_spawnattr_destroy(&attr);
-#if _lib_posix_spawn < 2
-	if (waitpid(pid, &err, WNOHANG|WNOWAIT) == pid && EXIT_STATUS(err) == 127)
-	{
-		while (waitpid(pid, NiL, 0) == -1 && errno == EINTR);
-		if (!access(path, X_OK))
-			errno = ENOEXEC;
-		pid = -1;
-	}
-#endif
 	return pid;
  bad:
 	posix_spawnattr_destroy(&attr);
diff --git a/src/lib/libast/man/spawnveg.3 b/src/lib/libast/man/spawnveg.3
index 4df6d0620..960614b82 100644
--- a/src/lib/libast/man/spawnveg.3
+++ b/src/lib/libast/man/spawnveg.3
@@ -68,7 +68,7 @@ are as in
 .L pgid
 controls the new process group and session:
 .TP
-.L <0
+.L -1
 The new process becomes a session leader.
 It is called in the child context.
 .TP
@@ -86,5 +86,12 @@ The
 .L spawnveg
 function cannot set the terminal process group.
 As a result, it is incompatible with job control when used with terminals.
+Additionally, if the
+.L POSIX_SPAWN_SETSID
+attribute is not supported, then
+.L spawnveg
+cannot make the new process a session leader when using the
+.I posix_spawn
+API.
 .SH "SEE ALSO"
-fork(2), exec(2), setpgid(2), setsid(2), spawnve(2)
+fork(2), posix_spawn(3), exec(2), setpgid(2), setsid(2), spawnve(2)