From 62b5da6f9975dc17657a31c65fa7f7e8032acf9e Mon Sep 17 00:00:00 2001
From: mpl <mathieu.lonjaret@gmail.com>
Date: Tue, 13 Nov 2012 23:31:07 +0100
Subject: [PATCH] find the path to the executable of the running instance to
 restart camli properly
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This change adds the functionality to find the path to
the currently running executable, so that camlistore
can be restarted without à priori knowledge of cwd.
It should work for linux, netBSD and freeBSD, and it
might work for openBSD.
The naive (os.Args[0]) approach is still used with
darwin.

Reference: https://codereview.appspot.com/6736069/

Change-Id: Icc9fc2b4e1b3542cfbe6c457c1fefbe762eff2f1
---
 pkg/osutil/restart_freebsd.go | 54 +++++++++++++++++++++++++++++++++++
 pkg/osutil/restart_unix.go    | 29 ++++++++++++++++++-
 2 files changed, 82 insertions(+), 1 deletion(-)
 create mode 100644 pkg/osutil/restart_freebsd.go

diff --git a/pkg/osutil/restart_freebsd.go b/pkg/osutil/restart_freebsd.go
new file mode 100644
index 000000000..a5202e6d9
--- /dev/null
+++ b/pkg/osutil/restart_freebsd.go
@@ -0,0 +1,54 @@
+// +build freebsd
+
+/*
+Copyright 2012 The Camlistore Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package osutil
+
+import (
+	"errors"
+	"os"
+	"runtime"
+	"syscall"
+	"unsafe"
+)
+
+func init() {
+	osSelfPath = selfPathFreeBSD
+}
+
+func selfPathFreeBSD() (string, error) {
+	mib := [4]int32{1 /* CTL_KERN */, 14 /* KERN_PROC */, 12 /* KERN_PROC_PATHNAME */, -1}
+
+	n := uintptr(0)
+	// get length
+	_, _, err := syscall.Syscall6(syscall.SYS__SYSCTL, uintptr(unsafe.Pointer(&mib[0])), 4, 0, uintptr(unsafe.Pointer(&n)), 0, 0)
+	if err != 0 {
+		return "", err
+	}
+	if n == 0 { // shouldn't happen
+		return "", nil
+	}
+	buf := make([]byte, n)
+	_, _, err = syscall.Syscall6(syscall.SYS__SYSCTL, uintptr(unsafe.Pointer(&mib[0])), 4, uintptr(unsafe.Pointer(&buf[0])), uintptr(unsafe.Pointer(&n)), 0, 0)
+	if err != 0 {
+		return "", err
+	}
+	if n == 0 { // shouldn't happen
+		return "", nil
+	}
+	return string(buf[:n-1]), nil
+}
diff --git a/pkg/osutil/restart_unix.go b/pkg/osutil/restart_unix.go
index 7c1eb64b1..a3a57940a 100644
--- a/pkg/osutil/restart_unix.go
+++ b/pkg/osutil/restart_unix.go
@@ -19,13 +19,40 @@ limitations under the License.
 package osutil
 
 import (
+	"errors"
 	"os"
+	"runtime"
 	"syscall"
 )
 
+// if non-nil, osSelfPath is used from selfPath.
+var osSelfPath func() (string, error)
+
+func selfPath() (string, error) {
+	if f := osSelfPath; f != nil {
+		return f()
+	}
+	switch runtime.GOOS {
+	case "linux":
+		return "/proc/self/exe", nil
+	case "netbsd":
+		return "/proc/curproc/exe", nil
+	case "openbsd":
+		return "/proc/curproc/file", nil
+	case "darwin":
+		// TODO(mpl): shall we do the whole dance for darwin, which requires modifying the runtime as well, if I understood minux's work correctly?
+		return os.Args[0], nil
+	}
+	return "", errors.New("No restart because selfPath() not implemented for " + runtime.GOOS)
+}
+
 // restartProcess returns an error if things couldn't be
 // restarted.  On success, this function never returns
 // because the process becomes the new process.
 func RestartProcess() error {
-	return syscall.Exec(os.Args[0], os.Args, os.Environ())
+	path, err := selfPath()
+	if err != nil {
+		return err
+	}
+	return syscall.Exec(path, os.Args, os.Environ())
 }