os: enable file creation w/ close-on-exec on darwin, freebsd

[mikioh]

Both OS X 10.7 and FreeBSD 8 support O_CLOEXEC, so there's no reason to hesitate to
enable it on supported kernels.

[bradfitz]

Comment 1:

Hesitate?  I think nobody even cared to spend the time yet.
I only did Linux to reduce lock contention.
Feel free to add Darwin and FreeBSD support, but it shouldn't block Go 1.3.

Labels changed: added release-go1.3maybe, removed release-go1.3.

[ianlancetaylor]

Comment 2:

The os package already uses O_CLOEXEC on all Unix systems.  See os/file_unix.go.
I don't understand what change you are proposing.

[mikioh]

Comment 3:

> I don't understand what change you are proposing.
Something like the following.
--- a/src/pkg/syscall/zerrors_freebsd_amd64.go
+++ b/src/pkg/syscall/zerrors_freebsd_amd64.go
+   O_CLOEXEC                         = 0x100000
--- a/src/pkg/os/file_unix.go
+++ b/src/pkg/os/file_unix.go
+// supportsCloseOnExec reports whether the platform supports the
+// O_CLOEXEC flag.
+var supportsCloseOnExec bool
+
-   if syscall.O_CLOEXEC == 0 || runtime.GOOS == "darwin" { // O_CLOEXEC not supported
+   if !supportsCloseOnExec {
--- /dev/null
+++ b/src/pkg/os/sys_freebsd.go
+package os
+
+import "syscall"
+
+func init() {
+   // The O_CLOEXEC flag was introduced in FreeBSD 8.3.
+   if osrel, err := syscall.SysctlUint32("kern.osreldate"); err == nil {
+       // See http://www.freebsd.org/doc/en/books/porters-handbook/freebsd-versions.html.
+       if osrel >= 803000 {
+           supportsCloseOnExec = true
+       }
+   }
+}

[ianlancetaylor]

Comment 4:

What happens if you pass O_CLOEXEC on FreeBSD versions before 8.2?  Can we check for
some appropriate error and retry without O_CLOEXEC, the way we handle SOCK_CLOEXEC?

[mikioh]

Comment 5:

Or...
if supportsCloseOnExec {
        flag |= syscall.O_CLOEXEC
}
r, e := syscall.Open(name, flag, syscallMode(perm))

[mikioh]

Comment 6:

> the way we handle SOCK_CLOEXEC?
Not sure whether such simple fallback works well, but will have a look at kernel code
tomorrow. Hm, probably kernel just ignores unsupported flags because,
./zerrors_darwin_386.go:    O_CLOEXEC                         = 0x1000000
./zerrors_darwin_amd64.go:  O_CLOEXEC                         = 0x1000000
but
if syscall.O_CLOEXEC == 0 || runtime.GOOS == "darwin" { // O_CLOEXEC not supported
sigh. According to https://code.google.com/p/go-wiki/wiki/DashboardBuilders, OS X 10.6
which includes BSD subsystem comes from FreeBSD shows us no error until now.

[mikioh]

Comment 7:

Confirmed, unlike IPC stuff such as socket or mmap, O_CLOEXEC is just ignored, sigh.
See fallocf in 8/9-STABLE or finstall in 10-STABLE.
http://svnweb.freebsd.org/base?view=revision&revision=220241

[mikioh]

Comment 8:

This issue was closed by revision be8aa4b.

Status changed to Fixed.