Implement support for POSIX_SPAWN_TCSETPGROUP & fix spawnveg bugs

This commit implements support for the glibc POSIX_SPAWN_TCSETPGROUP and
posix_spawnattr_tcsetpgrp_np extensions[1]. This was done with the intention
of improving performance in interactive shells without reintroducing previous
race conditions[2][3]. These changes were tested with glibc commit 342cc934.

src/cmd/ksh93/sh/path.c:
- Tell spawnveg to set the terminal process group when launching a child
  process in an interactive shell.

src/cmd/ksh93/sh/xec.c:
- Allow usage of spawnveg when posix_spawnattr_tcsetpgrp_np is available.
- Reimplement most of the sh_ntfork() SIGTSTP handling code removed in
  commit 66c3720.

src/lib/libast/comp/spawnveg.c,
src/lib/libast/misc/procopen.c,
src/lib/libast/features/sys:
- Add support for POSIX_SPAWN_TCSETPGROUP as implemented in glibc. This code
  (with a few changes) might also work on QNX, but I've avoided changing
  anything on that OS since I don't have a QNX system to test with.
- Bugfix 1: If pgid == -1, use POSIX_SPAWN_SETSID when it's available (spawnveg
  uses setsid(2) after fork/vfork, so it should do the same thing when
  posix_spawn is used instead.

src/lib/libast/man/spawnveg.3:
- Document the changes to spawnveg(3) in the corresponding man page. Currently
  spawnveg will only use the new tcfd argument if posix_spawnattr_tcsetpgrp_np
  is supported. This could also be implemented for the fork fallback, but for
  now I've avoided changing that since actually using it in the fork code
  would likely require a lot of hackery to avoid attempting tcsetpgrp with
  vfork (the behavior of tcsetpgrp after vfork is not portable) and would only
  benefit systems that don't have posix_spawn and vfork (I can't recall any off
  the top of my head that would fall under that category).

src/lib/libast/features/lib:
- Bugfix 2: Fix syntax errors in the posix_spawn feature test that caused ksh
  to fall back to vfork instead.
- Detect the existence of the GNU posix_spawnattr_tcsetpgrp_np() extension.

[1]: https://sourceware.org/git/?p=glibc.git;a=commit;h=342cc934a3bf74ac618e2318d738f22ac93257ba
[2]: #79
[3]: https://www.mail-archive.com/[email protected]/msg00717.html

src/cmd/ksh93/sh/path.c

@@ -140,7 +140,7 @@ static pid_t _spawnveg(const char *path, char* const argv[], char* const envp[],
 	while(1)
 	{
 		sh_stats(STAT_SPAWN);
-		pid = spawnveg(path,argv,envp,pgid);
+		pid = spawnveg(path,argv,envp,pgid,job.jobcontrol?job.fd:-1);
 		if(pid>=0 || errno!=EAGAIN)
 			break;
 	}

src/cmd/ksh93/sh/xec.c

@@ -1623,7 +1623,11 @@ int sh_exec(register const Shnode_t *t, int flags)
 					fifo_save_ppid = sh.current_pid;
 #endif
 #if SHOPT_SPAWN
+#if !_lib_posix_spawnattr_tcsetpgrp_np
 				if(com && !job.jobcontrol)
+#else
+				if(com)
+#endif /* !_lib_posix_spawnattr_tcsetpgrp_np */
 				{
 					parent = sh_ntfork(t,com,&jobid,ntflag);
 					if(parent<0)
@@ -3462,7 +3466,8 @@ static void sigreset(int mode)
 
 /*
  * A combined fork/exec for systems with slow fork().
- * Incompatible with job control on interactive shells (job.jobcontrol).
+ * Incompatible with job control on interactive shells (job.jobcontrol) if
+ * the system does not support posix_spawnattr_tcsetpgrp_np().
  */
 static pid_t sh_ntfork(const Shnode_t *t,char *argv[],int *jobid,int flag)
 {
@@ -3474,6 +3479,9 @@ static pid_t sh_ntfork(const Shnode_t *t,char *argv[],int *jobid,int flag)
 	char		**arge, *path;
 	volatile pid_t	grp = 0;
 	Pathcomp_t	*pp;
+#if _lib_posix_spawnattr_tcsetpgrp_np
+	volatile int	jobwasset=0;
+#endif /* _lib_posix_spawnattr_tcsetpgrp_np */
 	if(flag)
 	{
 		otype = savetype;
@@ -3538,8 +3546,21 @@ static pid_t sh_ntfork(const Shnode_t *t,char *argv[],int *jobid,int flag)
 		}
 		arge = sh_envgen();
 		sh.exitval = 0;
+#if _lib_posix_spawnattr_tcsetpgrp_np
+		if(job.jobcontrol)
+		{
+			signal(SIGTTIN,SIG_DFL);
+			signal(SIGTTOU,SIG_DFL);
+			signal(SIGTSTP,SIG_DFL);
+			jobwasset++;
+		}
+#endif /* _lib_posix_spawnattr_tcsetpgrp_np */
 #ifdef JOBS
+#if _lib_posix_spawnattr_tcsetpgrp_np
+		if(sh_isstate(SH_MONITOR) && (job.jobcontrol || (otype&FAMP)))
+#else
 		if(sh_isstate(SH_MONITOR) && (otype&FAMP))
+#endif /* _lib_posix_spawnattr_tcsetpgrp_np */
 		{
 			if((otype&FAMP) || job.curpgid==0)
 				grp = 1;
@@ -3600,6 +3621,17 @@ static pid_t sh_ntfork(const Shnode_t *t,char *argv[],int *jobid,int flag)
 	sh_popcontext(buffp);
 	if(buffp->olist)
 		free_list(buffp->olist);
+#if _lib_posix_spawnattr_tcsetpgrp_np
+	if(jobwasset)
+	{
+		signal(SIGTTIN,SIG_IGN);
+		signal(SIGTTOU,SIG_IGN);
+		if(sh_isstate(SH_INTERACTIVE))
+			signal(SIGTSTP,SIG_IGN);
+		else
+			signal(SIGTSTP,SIG_DFL);
+	}
+#endif /* _lib_posix_spawnattr_tcsetpgrp_np */
 	if(sigwasset)
 		sigreset(1);	/* restore ignored signals */
 	if(scope)

src/lib/libast/comp/spawnveg.c

@@ -32,6 +32,12 @@
 
 #include <ast.h>
 
+/* Make sure posix_spawn was detected correctly to avoid
+   creating difficult to debug race conditions. */
+#if !_lib_posix_spawn && _lib_posix_spawnattr_tcsetpgrp_np
+#error "The posix_spawn feature test is borked."
+#endif
+
 #if _lib_spawnveg
 
 NoN(spawnveg)
@@ -45,22 +51,38 @@ NoN(spawnveg)
 #include <wait.h>
 
 pid_t
-spawnveg(const char* path, char* const argv[], char* const envv[], pid_t pgid)
+spawnveg(const char* path, char* const argv[], char* const envv[], pid_t pgid, int tcfd)
 {
-	int			err;
+	int			err, flags = 0;
 	pid_t			pid;
 	posix_spawnattr_t	attr;
 
 	if (err = posix_spawnattr_init(&attr))
 		goto nope;
-	if (pgid)
+#if POSIX_SPAWN_SETSID
+	if (pgid == -1)
+		flags |= POSIX_SPAWN_SETSID;
+#endif
+	if (pgid > 0)
+	{
+		flags |= POSIX_SPAWN_SETPGROUP;
+#if _lib_posix_spawnattr_tcsetpgrp_np
+		if (tcfd >= 0)
+			flags |= POSIX_SPAWN_TCSETPGROUP;
+#endif
+	}
+	if (flags && (err = posix_spawnattr_setflags(&attr, flags)))
+		goto bad;
+	if (pgid > 0)
 	{
 		if (pgid <= 1)
 			pgid = 0;
 		if (err = posix_spawnattr_setpgroup(&attr, pgid))
 			goto bad;
-		if (err = posix_spawnattr_setflags(&attr, POSIX_SPAWN_SETPGROUP))
+#if _lib_posix_spawnattr_tcsetpgrp_np
+		if (tcfd >= 0 && (err = posix_spawnattr_tcsetpgrp_np(&attr, tcfd)))
 			goto bad;
+#endif
 	}
 	if (err = posix_spawn(&pid, path, NiL, &attr, argv, envv ? envv : environ))
 	{
@@ -99,8 +121,9 @@ spawnveg(const char* path, char* const argv[], char* const envv[], pid_t pgid)
 #endif
 
 pid_t
-spawnveg(const char* path, char* const argv[], char* const envv[], pid_t pgid)
+spawnveg(const char* path, char* const argv[], char* const envv[], pid_t pgid, int tcfd)
 {
+	NOT_USED(tcfd);
 #if defined(P_DETACH)
 	return spawnve(pgid ? P_DETACH : P_NOWAIT, path, argv, envv ? envv : environ);
 #else
@@ -119,10 +142,11 @@ spawnveg(const char* path, char* const argv[], char* const envv[], pid_t pgid)
  */
 
 pid_t
-spawnveg(const char* path, char* const argv[], char* const envv[], pid_t pgid)
+spawnveg(const char* path, char* const argv[], char* const envv[], pid_t pgid, int tcfd)
 {
 	struct inheritance	inherit;
 
+	NOT_USED(tcfd);
 	inherit.flags = 0;
 	if (pgid)
 	{
@@ -156,7 +180,7 @@ spawnveg(const char* path, char* const argv[], char* const envv[], pid_t pgid)
  */
 
 pid_t
-spawnveg(const char* path, char* const argv[], char* const envv[], pid_t pgid)
+spawnveg(const char* path, char* const argv[], char* const envv[], pid_t pgid, int tcfd)
 {
 #if _lib_fork || _lib_vfork
 	int			n;
@@ -171,6 +195,7 @@ spawnveg(const char* path, char* const argv[], char* const envv[], pid_t pgid)
 #endif
 #endif
 
+	NOT_USED(tcfd);
 	if (!envv)
 		envv = environ;
 #if _lib_spawnve
@@ -213,15 +238,16 @@ spawnveg(const char* path, char* const argv[], char* const envv[], pid_t pgid)
 				pgid = getpid();
 			if (setpgid(0, pgid) < 0 && errno == EPERM)
 				setpgid(pgid, 0);
-#if _lib_tcgetpgrp
 			if (m)
+			{
+#if _lib_tcgetpgrp
 				tcsetpgrp(2, pgid);
 #else
 #ifdef TIOCSPGRP
-			if (m)
 				ioctl(2, TIOCSPGRP, &pgid);
 #endif
 #endif
+			}
 		}
 		execve(path, argv, envv);
 #if _real_vfork

src/lib/libast/features/lib

@@ -240,9 +240,9 @@ tst	lib_posix_spawn unistd.h stdlib.h spawn.h -Dfork=______fork note{ posix_spaw
 	#include <string.h>
 	/* if it uses fork() why bother? */
 	#undef fork
-	pid_t fork(void)) { NOTE("uses fork()"; return -1; }
-	pid_t _fork(void)) { NOTE("uses _fork()"; return -1; }
-	pid_t __fork(void)) { NOTE("uses __fork()"; return -1; }
+	pid_t fork(void) { NOTE("uses fork()"); return -1; }
+	pid_t _fork(void) { NOTE("uses _fork()"); return -1; }
+	pid_t __fork(void) { NOTE("uses __fork()"); return -1; }
 	int
 	main(argc, argv)
 	int	argc;
@@ -343,6 +343,7 @@ tst	lib_posix_spawn unistd.h stdlib.h spawn.h -Dfork=______fork note{ posix_spaw
 		_exit(n);
  	}
 }end
+lib	posix_spawnattr_tcsetpgrp_np
 
 tst	lib_spawn_mode unistd.h stdlib.h note{ first spawn arg is mode and it works }end execute{
 	#include <signal.h>

src/lib/libast/features/sys

@@ -195,7 +195,7 @@ extern	setpgid		int		(pid_t, pid_t)
 extern	setsid		pid_t		(void)
 extern	setuid		int		(uid_t)
 extern	sleep		unsigned		(unsigned int)
-extern	spawnveg	pid_t		(const char*, char* const[], char* const[], pid_t)
+extern	spawnveg	pid_t		(const char*, char* const[], char* const[], pid_t, int)
 extern	srand		void		(unsigned int)
 extern	strcasecmp	int		(const char*, const char*)
 extern	strcat		char*		(char*, const char*)

src/lib/libast/man/spawnveg.3

@@ -42,7 +42,7 @@ spawnveg \- process spawn with process group and session control
 .SH SYNOPSIS
 .L "#include <ast.h>"
 .sp
-.L "int spawnveg(const char* command, char** argv, char** envv, pid_t pgid);"
+.L "int spawnveg(const char* command, char** argv, char** envv, pid_t pgid, int tcfd);"
 .SH DESCRIPTION
 .L spawnveg
 combines
@@ -81,10 +81,35 @@ The new process becomes a process group leader.
 .L >1
 The new process joins the process group
 .IR pgid .
-.SH CAVEATS
+.PP
 The
+.L tcfd
+argument is currently only used if the operating system supports the
+.I posix_spawnattr_tcsetpgrp_np
+function.
+When
+.L tcfd
+is
+.L >=0
+and
+.L pgid
+is
+.LR >0 ,
+spawnveg will set the controlling terminal for the new process to
+.IR tcfd .
+.SH CAVEATS
+If the
+.I posix_spawnattr_tcsetpgrp_np
+function is not available, then
 .L spawnveg
-function cannot set the terminal process group.
+cannot reliably 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)

src/lib/libast/misc/procopen.c

@@ -744,7 +744,7 @@ sfsync(sfstderr);
 			if (forked || (flags & PROC_OVERLAY))
 				execve(path, p, environ);
 #if _use_spawnveg
-			else if ((proc->pid = spawnveg(path, p, environ, proc->pgrp)) != -1)
+			else if ((proc->pid = spawnveg(path, p, environ, proc->pgrp, -1)) != -1)
 				goto cleanup;
 #endif
 			if (errno != ENOEXEC)
@@ -773,7 +773,7 @@ sfsync(sfstderr);
 			execve(env + 2, p, environ);
 #if _use_spawnveg
 		else
-			proc->pid = spawnveg(env + 2, p, environ, proc->pgrp);
+			proc->pid = spawnveg(env + 2, p, environ, proc->pgrp, -1);
 #endif
 	cleanup:
 		if (forked)