Implement support for POSIX_SPAWN_TCSETPGROUP (#438)

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.

[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:
- 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.

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:
- Detect the existence of the GNU posix_spawnattr_tcsetpgrp_np()
  extension.
- Do not detect an OS spawnveg(3). With the API changes to spawnveg
  in this pull request ksh probably can't use the OS's spawnveg
  function anymore. (That's assuming anything else even provides a
  spawnveg function to begin with, which is unlikely.)

src/lib/libast/features/api,
src/cmd/ksh93/include/defs.h:
- Bump libast version (20220101 => 20220201) due to the spawnveg(3)
  API change.

src/cmd/ksh93/include/defs.h

@@ -29,8 +29,8 @@
 #define defs_h_defined
 
 #include	<ast.h>
-#if !defined(AST_VERSION) || AST_VERSION < 20220101
-#error libast version 20220101 or later is required
+#if !defined(AST_VERSION) || AST_VERSION < 20220201
+#error libast version 20220201 or later is required
 #endif
 #if !_lib_fork
 #error In 2021, ksh joined the 21st century and started requiring fork(2).

src/cmd/ksh93/sh/path.c

@@ -147,7 +147,7 @@ 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

@@ -55,6 +55,10 @@
 #   include <sys/resource.h>
 #endif
 
+#if _lib_posix_spawn > 1 && _lib_posix_spawnattr_tcsetpgrp_np
+#define _use_ntfork_tcpgrp 1
+#endif
+
 #define SH_NTFORK	SH_TIMING
 #define NV_BLTPFSH	NV_ARRAY
 
@@ -1613,7 +1617,11 @@ int sh_exec(register const Shnode_t *t, int flags)
 					fifo_save_ppid = sh.current_pid;
 #endif
 #if SHOPT_SPAWN
+#if _use_ntfork_tcpgrp
+				if(com)
+#else
 				if(com && !job.jobcontrol)
+#endif /* _use_ntfork_tcpgrp */
 				{
 					parent = sh_ntfork(t,com,&jobid,ntflag);
 					if(parent<0)
@@ -3444,7 +3452,8 @@ 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)
 {
@@ -3456,6 +3465,9 @@ 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 _use_ntfork_tcpgrp
+	volatile int	jobwasset=0;
+#endif /* _use_ntfork_tcpgrp */
 	if(flag)
 	{
 		otype = savetype;
@@ -3520,8 +3532,21 @@ static pid_t sh_ntfork(const Shnode_t *t,char *argv[],int *jobid,int flag)
 		}
 		arge = sh_envgen();
 		sh.exitval = 0;
+#if _use_ntfork_tcpgrp
+		if(job.jobcontrol)
+		{
+			signal(SIGTTIN,SIG_DFL);
+			signal(SIGTTOU,SIG_DFL);
+			signal(SIGTSTP,SIG_DFL);
+			jobwasset++;
+		}
+#endif /* _use_ntfork_tcpgrp */
 #ifdef JOBS
+#if _use_ntfork_tcpgrp
+		if(sh_isstate(SH_MONITOR) && (job.jobcontrol || (otype&FAMP)))
+#else
 		if(sh_isstate(SH_MONITOR) && (otype&FAMP))
+#endif /* _use_ntfork_tcpgrp */
 		{
 			if((otype&FAMP) || job.curpgid==0)
 				grp = 1;
@@ -3582,6 +3607,17 @@ 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 _use_ntfork_tcpgrp
+	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 /* _use_ntfork_tcpgrp */
 	if(sigwasset)
 		sigreset(1);	/* restore ignored signals */
 	if(scope)

src/lib/libast/comp/spawnveg.c

@@ -32,20 +32,14 @@
 
 #include <ast.h>
 
-#if _lib_spawnveg
-
-NoN(spawnveg)
-
-#else
-
 #if _lib_posix_spawn > 1	/* reports underlying exec() errors */
 
 #include <spawn.h>
 #include <error.h>
 #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, flags = 0;
 	pid_t			pid;
@@ -59,7 +53,13 @@ spawnveg(const char* path, char* const argv[], char* const envv[], pid_t pgid)
 	else
 #endif
 	if (pgid)
+	{
 		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 && pgid != -1)
@@ -68,6 +68,10 @@ spawnveg(const char* path, char* const argv[], char* const envv[], pid_t pgid)
 			pgid = 0;
 		if (err = posix_spawnattr_setpgroup(&attr, pgid))
 			goto bad;
+#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))
 	{
@@ -97,8 +101,9 @@ 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
@@ -117,10 +122,11 @@ 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)
 	{
@@ -154,7 +160,7 @@ 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;
@@ -169,6 +175,7 @@ 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
@@ -214,11 +221,9 @@ spawnveg(const char* path, char* const argv[], char* const envv[], pid_t pgid)
 #if _lib_tcgetpgrp
 			if (m)
 				tcsetpgrp(2, pgid);
-#else
-#ifdef TIOCSPGRP
+#elif defined(TIOCSPGRP)
 			if (m)
 				ioctl(2, TIOCSPGRP, &pgid);
-#endif
 #endif
 		}
 		execve(path, argv, envv);
@@ -289,5 +294,3 @@ spawnveg(const char* path, char* const argv[], char* const envv[], pid_t pgid)
 #endif
 
 #endif
-
-#endif

src/lib/libast/features/api

@@ -1,6 +1,6 @@
 iff AST_API
 
-ver ast 20220101
+ver ast 20220201
 
 api ast 20120528 regexec regnexec regrexec regsubexec strgrpmatch
 

src/lib/libast/features/lib

@@ -36,7 +36,7 @@ lib	mount,onexit,opendir,pathconf
 lib	readlink,remove,rename,rewinddir,rindex,rmdir,setlocale
 lib	setpgid,setpgrp,setpgrp2,setreuid,setsid,setuid,sigaction
 lib	sigprocmask,sigsetmask,sigunblock,sigvec,socketpair
-lib	spawn,spawnve,spawnveg
+lib	spawn,spawnve
 lib	strchr,strcoll,strdup,strerror,strcasecmp,strncasecmp,strrchr,strstr
 lib	strmode,strxfrm,strftime,swab,symlink,sysconf,sysinfo,syslog
 lib	telldir,tmpnam,tzset,universe,unlink,utime,wctype
@@ -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>
@@ -642,7 +643,7 @@ tst	- output{
 		printf("\n");
 	#endif
 
-	#if _lib_spawnveg || _lib_posix_spawn || _lib_spawn_mode || _lib_spawn && _hdr_spawn && _mem_pgroup_inheritance || _lib_vfork && _real_vfork
+	#if _lib_posix_spawn || _lib_spawn_mode || _lib_spawn && _hdr_spawn && _mem_pgroup_inheritance || _lib_vfork && _real_vfork
 		printf("#if !_AST_no_spawnveg\n");
 		printf("#define _use_spawnveg	1\n");
 		printf("#endif\n");

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 +81,28 @@ 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

src/lib/libast/misc/procopen.c

@@ -2,7 +2,7 @@
 *                                                                      *
 *               This software is part of the ast package               *
 *          Copyright (c) 1985-2012 AT&T Intellectual Property          *
-*          Copyright (c) 2020-2021 Contributors to ksh 93u+m           *
+*          Copyright (c) 2020-2022 Contributors to ksh 93u+m           *
 *                      and is licensed under the                       *
 *                 Eclipse Public License, Version 1.0                  *
 *                    by AT&T Intellectual Property                     *
@@ -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)