Implement support for POSIX_SPAWN_TCSETPGROUP & fix spawnveg bugs

Note that this is still a WIP. Current TODOs:
  - Error out if posix_spawnattr_tcsetpgrp_np is detected but
    posix_spawn is not.
  - Document the changes to spawnveg in the relevant man page.
  - Maybe: Use tcsetpgrp in the spawnveg fork fallback (if this is
    implemented, vfork will not be allowed to use that function since the
    behavior of tcsetpgrp after vfork is unpredictable and not portable).

This commit implements support for the glibc POSIX_SPAWN_TCSETPGROUP and
posix_spawnattr_tcsetpgrp_np extension [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 posix_spawn 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/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 posix_spawnattr_tcsetpgrp_np().

[1]: https://sourceware.org/git/?p=glibc.git;a=commit;h=342cc934a3bf74ac618e2318d738f22ac93257ba
[2]: ksh93#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 the POSIX_SPAWN_TCSETPGROUP flag.
  */
 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

@@ -44,23 +44,44 @@ NoN(spawnveg)
 #include <error.h>
 #include <wait.h>
 
+#if !_lib_posix_spawn
+#error "DEBUG ERROR 1"
+#elif !_lib_posix_spawnattr_tcsetpgrp_np
+#error "DEBUG ERROR 2"
+#elif !POSIX_SPAWN_TCSETPGROUP
+#error "DEBUG ERROR 3"
+#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)
 {
-	int			err;
+	int			err, flags = 0;
 	pid_t			pid;
 	posix_spawnattr_t	attr;
 
 	if (err = posix_spawnattr_init(&attr))
 		goto nope;
 	if (pgid)
 	{
+		flags |= POSIX_SPAWN_SETPGROUP;
+#if _lib_posix_spawnattr_tcsetpgrp_np
+		if (tcfd >= 0)
+			flags |= POSIX_SPAWN_TCSETPGROUP;
+#endif
+#if POSIX_SPAWN_SETSID
+		if (pgid == -1)
+			flags |= POSIX_SPAWN_SETSID;
+#endif
+		if (err = posix_spawnattr_setflags(&attr, flags))
+			goto bad;
 		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 +120,9 @@ 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 +141,11 @@ 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 +179,7 @@ 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 +194,7 @@ 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

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/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)