internal/syscall: Adjust Pipe to take flags

This way e.g. O_CLOEXEC can be passed in at pipe creation time removing
potential race in between pipe+fcntl vs exec in the middle. It will also
help in windows porting in follow-up patches becuase there is no fcntl
on Windows, but pipe with O_CLOEXEC semantic can be created directly
with flags=_O_NOINHERIT.

golang/_compat/windows/unistd.h

@@ -26,4 +26,6 @@
 
 #include <io.h>
 
+#define O_CLOEXEC  _O_NOINHERIT
+
 #endif  // _NXD_LIBGOLANG_COMPAT_WIN_UNISTD_H

golang/os.cpp

@@ -249,7 +249,7 @@ tuple<string, error> ReadFile(const string& path) {
 
 tuple<File, File, error> Pipe() {
     int vfd[2], syserr;
-    syserr = sys::Pipe(vfd);
+    syserr = sys::Pipe(vfd, 0);
     if (syserr != 0)
         return make_tuple(nil, nil, fmt::errorf("pipe: %w", sys::NewErrno(syserr)));
 

golang/os/signal.cpp

-// Copyright (C) 2021-2022  Nexedi SA and Contributors.
+// Copyright (C) 2021-2023  Nexedi SA and Contributors.
 //                          Kirill Smelkov <kirr@nexedi.com>
 //
 // This program is free software: you can Use, Study, Modify and Redistribute
@@ -160,10 +160,8 @@ void _init() {
 
     // create _wakerx <-> _waketx pipe; set _waketx to nonblocking mode
     int vfd[2];
-    if (sys::Pipe(vfd) < 0)
+    if (sys::Pipe(vfd, O_CLOEXEC) < 0)
         panic("pipe(_wakerx, _waketx)");        // TODO +syserr
-    if (sys::Fcntl(vfd[0], F_SETFD, FD_CLOEXEC) < 0)
-        panic("fcntl(_wakerx, FD_CLOEXEC)");    // TODO +syserr
     error err;
     tie(_wakerx, err) = os::NewFile(vfd[0], "_wakerx");
     if (err != nil)
@@ -171,8 +169,6 @@ void _init() {
     _waketx = vfd[1];
     if (sys::Fcntl(_waketx, F_SETFL, O_NONBLOCK) < 0)
         panic("fcntl(_waketx, O_NONBLOCK)");    // TODO +syserr
-    if (sys::Fcntl(_waketx, F_SETFD, FD_CLOEXEC) < 0)
-        panic("fcntl(_waketx, FD_CLOEXEC)");    // TODO +syserr
 
     _actIgnore.sa_handler = SIG_IGN;
     _actIgnore.sa_flags   = 0;

golang/runtime/internal/syscall.cpp

-// Copyright (C) 2021-2022  Nexedi SA and Contributors.
+// Copyright (C) 2021-2023  Nexedi SA and Contributors.
 //                          Kirill Smelkov <kirr@nexedi.com>
 //
 // This program is free software: you can Use, Study, Modify and Redistribute
@@ -126,9 +126,30 @@ int Open(const char *path, int flags, mode_t mode) {
     return fd;
 }
 
-__Errno Pipe(int vfd[2]) {
+__Errno Pipe(int vfd[2], int flags) {
+    // supported flags: O_CLOEXEC
+    if (flags & ~(O_CLOEXEC))
+        return -EINVAL;
     int save_errno = errno;
-    int err = ::pipe(vfd);
+    int err;
+#ifdef __linux__
+    err = ::pipe2(vfd, flags);
+#else
+    err = ::pipe(vfd);
+    if (err)
+        goto out;
+    if (flags & O_CLOEXEC) {
+        for (int i=0; i<2; i++) {
+            err = Fcntl(vfd[i], F_SETFD, FD_CLOEXEC);
+            if (err) {
+                Close(vfd[0]);
+                Close(vfd[1]);
+                goto out;
+            }
+        }
+    }
+out:
+#endif
     if (err == -1)
         err = -errno;
     errno = save_errno;

golang/runtime/internal/syscall.h

@@ -66,7 +66,7 @@ LIBGOLANG_API __Errno Close(int fd);
 LIBGOLANG_API __Errno Fcntl(int fd, int cmd, int arg);
 LIBGOLANG_API __Errno Fstat(int fd, struct ::stat *out_st);
 LIBGOLANG_API int/*fd|err*/ Open(const char *path, int flags, mode_t mode);
-LIBGOLANG_API __Errno Pipe(int vfd[2]);
+LIBGOLANG_API __Errno Pipe(int vfd[2], int flags);
 LIBGOLANG_API __Errno Sigaction(int signo, const struct ::sigaction *act, struct ::sigaction *oldact);