Commit ff612334fa8af05c42b71f784dff521899026f97 | zig

author	Josh Megnauth <jo.sh@tutanota.com> 2026-04-09 14:53:40-04:00
committer	Andrew Kelley <andrew@ziglang.org> 2026-04-17 23:13:39+02:00
log	ff612334fa8af05c42b71f784dff521899026f97
tree	cc89f0c97619c35f704842d5913a4b435fd23d24
parent	6e987a1d04e5d9eb41a10110a5343384f0a9a57b

libzigc: dup2 and dup3

This commit adds `dup2` and `dup3` based on musl. Zig already has
wrappers for the syscalls, but musl's implementation checks for a rare,
temporary race condition with dup2/3 and `open`. Like musl, this
implementation adds a fallback for dup3 if the syscall isn't available.

Contributes to: #30978

4 files changed, 27 insertions(+), 48 deletions(-)

lib
- c
  - unistd.zig
- libc
  - musl
    src
    unistd
    dup2.c
    dup3.c
src
- libs
  - musl.zig

lib/c/unistd.zig+27

...	...	@@ -21,6 +21,8 @@ comptime {
21	21	symbol(&chrootLinux, "chroot");
22	22	symbol(&ctermidLinux, "ctermid");
23	23	symbol(&dupLinux, "dup");
	24	symbol(&dup2Linux, "dup2");
	25	symbol(&dup3Linux, "dup3");
24	26
25	27	symbol(&getegidLinux, "getegid");
26	28	symbol(&geteuidLinux, "geteuid");
...	...	@@ -101,6 +103,31 @@ fn dupLinux(fd: c_int) callconv(.c) c_int {
101	103	return errno(linux.dup(fd));
102	104	}
103	105
	106	fn dup2Linux(old: c_int, new: c_int) callconv(.c) c_int {
	107	const busy: usize = @bitCast(-@as(isize, @intFromEnum(linux.E.BUSY)));
	108	var res = busy;
	109	while (res == busy) res = linux.dup2(old, new);
	110	return errno(res);
	111	}
	112
	113	fn dup3Linux(old: c_int, new: c_int, flags: c_int) callconv(.c) c_int {
	114	const busy: usize = @bitCast(-@as(isize, @intFromEnum(linux.E.BUSY)));
	115	var res = busy;
	116
	117	if (@hasField(linux.SYS, "dup3")) {
	118	while (res == busy) res = linux.dup3(old, new, @intCast(flags));
	119	} else if (@hasField(linux.SYS, "dup2")) {
	120	const cloexec: c_int = @bitCast(linux.O{ .CLOEXEC = true });
	121	const inval: usize = @bitCast(-@as(isize, @intFromEnum(linux.E.INVAL)));
	122	if (old == new or (flags & ~cloexec != 0)) return errno(inval);
	123	while (res == busy) res = linux.dup2(old, new);
	124	_ = if (res >= 0 and (flags & cloexec == cloexec)) linux.fcntl(new, linux.F.SETFD, linux.FD_CLOEXEC);
	125	} else {
	126	return errno(@bitCast(-@as(isize, @intFromEnum(linux.E.NOSYS))));
	127	}
	128	return errno(res);
	129	}
	130
104	131	fn getegidLinux() callconv(.c) linux.gid_t {
105	132	return linux.getegid();
106	133	}

lib/libc/musl/src/unistd/dup2.c deleted-20

...	...	@@ -1,20 +0,0 @@
1		#include <unistd.h>
2		#include <errno.h>
3		#include <fcntl.h>
4		#include "syscall.h"
5
6		int dup2(int old, int new)
7		{
8		int r;
9		#ifdef SYS_dup2
10		while ((r=__syscall(SYS_dup2, old, new))==-EBUSY);
11		#else
12		if (old==new) {
13		r = __syscall(SYS_fcntl, old, F_GETFD);
14		if (r >= 0) return old;
15		} else {
16		while ((r=__syscall(SYS_dup3, old, new, 0))==-EBUSY);
17		}
18		#endif
19		return __syscall_ret(r);
20		}

lib/libc/musl/src/unistd/dup3.c deleted-26

...	...	@@ -1,26 +0,0 @@
1		#define _GNU_SOURCE
2		#include <unistd.h>
3		#include <errno.h>
4		#include <fcntl.h>
5		#include "syscall.h"
6
7		int __dup3(int old, int new, int flags)
8		{
9		int r;
10		#ifdef SYS_dup2
11		if (old==new) return __syscall_ret(-EINVAL);
12		if (flags) {
13		while ((r=__syscall(SYS_dup3, old, new, flags))==-EBUSY);
14		if (r!=-ENOSYS) return __syscall_ret(r);
15		if (flags & ~O_CLOEXEC) return __syscall_ret(-EINVAL);
16		}
17		while ((r=__syscall(SYS_dup2, old, new))==-EBUSY);
18		if (r >= 0 && (flags & O_CLOEXEC))
19		__syscall(SYS_fcntl, new, F_SETFD, FD_CLOEXEC);
20		#else
21		while ((r=__syscall(SYS_dup3, old, new, flags))==-EBUSY);
22		#endif
23		return __syscall_ret(r);
24		}
25
26		weak_alias(__dup3, dup3);

src/libs/musl.zig-2

...	...	@@ -1758,8 +1758,6 @@ const src_files = [_][]const u8{
1758	1758	"musl/src/time/wcsftime.c",
1759	1759	"musl/src/time/__year_to_secs.c",
1760	1760	"musl/src/unistd/alarm.c",
1761		"musl/src/unistd/dup2.c",
1762		"musl/src/unistd/dup3.c",
1763	1761	"musl/src/unistd/faccessat.c",
1764	1762	"musl/src/unistd/fchdir.c",
1765	1763	"musl/src/unistd/fchown.c",