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Support glibc 2.35's posix_spawn_file_actions_addtcsetpgrp_np(3)

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This commit implements support for the glibc 2.35
posix_spawn_file_actions_addtcsetpgrp_np(3) extension[2][3],
updating spawnveg(3) to use the new function for setting the
terminal group. This was done with the intention of improving
performance in interactive shells without reintroducing previous
race conditions[4][5].

[1]: https://sourceware.org/pipermail/libc-alpha/2022-February/136040.html
[2]: https://sourceware.org/git/?p=glibc.git;a=commit;h=342cc934
[3]: https://sourceware.org/git/?p=glibc.git;a=commit;h=6289d28d
[4]: https://github.com/ksh93/ksh/issues/79
[5]: https://www.mail-archive.com/ast-developers@research.att.com/msg00717.html

src/cmd/ksh93/sh/path.c:
- Tell spawnveg(3) to set the terminal process group when launching
  a child process in an interactive shell.

src/cmd/ksh93/sh/xec.c:
- If posix_spawn_file_actions_addtcsetpgrp_np(3) is available,
  allow use of spawnveg(3) (via sh_ntfork()) even with job control
  active.
- sh_ntfork(): Reimplement most of the SIGTSTP handling code
  removed in commit 66c37202.

src/lib/libast/comp/spawnveg.c,
src/lib/libast/misc/procopen.c,
src/lib/libast/features/sys:
- Add support for posix_spawn_file_actions_addtcsetpgrp_np(3).
- Allow spawnveg to set the terminal process group when pgid == 0.
  This was necessary to avoid race conditions when using the new
  function.

src/lib/libast/features/lib:
- Detect posix_spawn_file_actions_addtcsetpgrp_np(3).
- 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/lib/libast/man/spawnveg.3:
- Document the changes to spawnveg(3) in the corresponding man
  page. Currently, it will only use the new tcfd argument if
  posix_spawn_file_actions_addtcsetpgrp_np(3) is supported. This
  could also be implemented for the fork(2) 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).
- Updated the man page to account for spawnveg's change in
  behavior.

Co-authored-by: Martijn Dekker <martijn@inlv.org>
This commit is contained in:
Johnothan King 2022-02-05 13:14:39 +00:00 • committed by Martijn Dekker
parent c7a774d9df
commit 0863a8eb29
9 changed files with 101 additions and 35 deletions
Download patch file Download diff file Expand all files Collapse all files

4
src/cmd/ksh93/include/defs.h
View file

@ -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).

2
src/cmd/ksh93/sh/path.c
View file

@ -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;
}

38
src/cmd/ksh93/sh/xec.c
View file

@ -55,6 +55,10 @@
# include <sys/resource.h>
#endif
#if _lib_posix_spawn > 1 && _lib_posix_spawn_file_actions_addtcsetpgrp_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)
@ -3449,7 +3457,8 @@ 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_spawn_file_actions_addtcsetpgrp_np().
*/
static pid_t sh_ntfork(const Shnode_t *t,char *argv[],int *jobid,int flag)
{
@ -3461,6 +3470,9 @@ 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;
@ -3525,8 +3537,21 @@ 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;
@ -3587,6 +3612,17 @@ 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)