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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

57
src/lib/libast/comp/spawnveg.c
View file

@ -32,12 +32,6 @@
#include <ast.h>
#if _lib_spawnveg
NoN(spawnveg)
#else
#if _lib_posix_spawn > 1 /* reports underlying exec() errors */
#include <spawn.h>
@ -45,20 +39,22 @@ 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, flags = 0;
pid_t pid;
posix_spawnattr_t attr;
int err, flags = 0;
pid_t pid;
posix_spawnattr_t attr;
#if _lib_posix_spawn_file_actions_addtcsetpgrp_np
posix_spawn_file_actions_t actions;
#endif
if (err = posix_spawnattr_init(&attr))
goto nope;
#if POSIX_SPAWN_SETSID
if (pgid == -1)
flags |= POSIX_SPAWN_SETSID;
else
#endif
if (pgid)
if (pgid && pgid != -1)
flags |= POSIX_SPAWN_SETPGROUP;
if (flags && (err = posix_spawnattr_setflags(&attr, flags)))
goto bad;
@ -69,13 +65,33 @@ spawnveg(const char* path, char* const argv[], char* const envv[], pid_t pgid)
if (err = posix_spawnattr_setpgroup(&attr, pgid))
goto bad;
}
#if _lib_posix_spawn_file_actions_addtcsetpgrp_np
if (tcfd >= 0)
{
if (err = posix_spawn_file_actions_init(&actions))
goto bad;
if (err = posix_spawn_file_actions_addtcsetpgrp_np(&actions, tcfd))
goto fail;
}
if (err = posix_spawn(&pid, path, (tcfd >= 0) ? &actions : NiL, &attr, argv, envv ? envv : environ))
#else
if (err = posix_spawn(&pid, path, NiL, &attr, argv, envv ? envv : environ))
#endif
{
if ((err != EPERM) || (err = posix_spawn(&pid, path, NiL, NiL, argv, envv ? envv : environ)))
goto bad;
goto fail;
}
#if _lib_posix_spawn_file_actions_addtcsetpgrp_np
if (tcfd >= 0)
posix_spawn_file_actions_destroy(&actions);
#endif
posix_spawnattr_destroy(&attr);
return pid;
fail:
#if _lib_posix_spawn_file_actions_addtcsetpgrp_np
if (tcfd >= 0)
posix_spawn_file_actions_destroy(&actions);
#endif
bad:
posix_spawnattr_destroy(&attr);
nope:
@ -97,8 +113,9 @@ 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 +134,11 @@ 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 +172,7 @@ 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 +187,7 @@ 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 +233,9 @@ 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 +306,3 @@ spawnveg(const char* path, char* const argv[], char* const envv[], pid_t pgid)
#endif
#endif
#endif