Subject: Re: [PATCH 2/2] mingw: ensure temporary file handles are not inherited by child processes

From: Junio C Hamano <[email-masked]>
Date: Thu, 18 Aug 2016 14:53:03 -0700

Eric Wong <[email-masked]> writes:

> O_CLOEXEC only exists since Linux 2.6.23 and there are likely
> still LTS (CentOS 5.x?) and non-Linux systems which do not have
> it, as well as machines with could have it defined in userspace
> headers but not have it in the kernel.
>
> So I suggest something like the following: (untested)
>
> #define GIT_O_TMP (O_RDWR | O_CREAT | O_EXCL)
>
> #ifndef O_CLOEXEC
> #  define O_CLOEXEC 0
> #endif
> 	/* state: -1=unknown; 0=broken; 1=working */
> 	static int cloexec_state = O_CLOEXEC == 0 ? 0 : -1;
> 	static int GIT_O_ETMP = (GIT_O_TMP | O_CLOEXEC)
>
> 	int fd = open(filename, GIT_O_ETMP, 0666);
> ...
> 	/*
> 	 * This is racy in the presence of threads,
> 	 * but the best we can do for old *nix:
> 	 */
> #if defined(F_GETFD) && defined(F_SETFD) && defined(FD_CLOEXEC)
> 	if (fd >= 0 && cloexec_state != 1) {
> 		int flags = fcntl(fd, F_GETFD);
>
> 		if (flags == -1)
> 			die_errno("F_GETFD failed");
> 		if (flags & O_CLOEXEC)
> 			cloexec_state = 1;
> 		else {
> 			flags = fcntl(fd, F_SETFD, flags | FD_CLOEXEC);
> 			if (flags == -1)
> 				die_errno("F_SETFD failed");
> 			cloexec_state = 0;
>
> 		}
> 	}
> #endif
> 	...

Our codepaths themselves generally do not care about O_CLOEXEC, so
giving a racy emulation of it is not worth the effort, making the
later half of the above an overkill.  Perhaps the three lines to
define O_CLOEXEC to 0 on older UNIX might be sufficient.