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adjust posix_spawn dup2 action behavior to match future requirements 

the resolution to Austin Group issue #411 defined new semantics for
the posix_spawn dup2 file action in the (previously useless) case
where src and dest fd are equal. future issues will require the dup2
file action to remove the close-on-exec flag. without this change,
passing fds to a child with posix_spawn while avoiding fd-leak races
in a multithreaded parent required a complex dance with temporary fds.

based on patch by Petr Skocik. changes were made to preserve the
80-column formatting of the function and to remove code that became
unreachable as a result of the new functionality.
This commit is contained in:
Rich Felker 2017-11-05 17:26:48 -05:00
parent eb03bde2f2
commit 6fc6ca1a32
1 changed files with 12 additions and 8 deletions
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20
src/process/posix_spawn.c
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@ -27,12 +27,7 @@ static int __sys_dup2(int old, int new)
#ifdef SYS_dup2
return __syscall(SYS_dup2, old, new);
#else
if (old==new) {
int r = __syscall(SYS_fcntl, old, F_GETFD);
return r<0 ? r : old;
} else {
return __syscall(SYS_dup3, old, new, 0);
}
return __syscall(SYS_dup3, old, new, 0);
#endif
}
@ -109,8 +104,17 @@ static int child(void *args_vp)
__syscall(SYS_close, op->fd);
break;
case FDOP_DUP2:
if ((ret=__sys_dup2(op->srcfd, op->fd))<0)
goto fail;
fd = op->srcfd;
if (fd != op->fd) {
if ((ret=__sys_dup2(fd, op->fd))<0)
goto fail;
} else {
ret = __syscall(SYS_fcntl, fd, F_GETFD);
ret = __syscall(SYS_fcntl, fd, F_SETFD,
ret & ~FD_CLOEXEC);
if (ret<0)
goto fail;
}
break;
case FDOP_OPEN:
fd = __sys_open(op->path, op->oflag, op->mode);