Start work on a SHM implementation in Go

tools/utils/shm/shm_fs.go

@@ -0,0 +1,36 @@
+// License: GPLv3 Copyright: 2022, Kovid Goyal, <kovid at kovidgoyal.net>
+//go:build linux || netbsd
+
+package shm
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+)
+
+var _ = fmt.Print
+
+func create_temp(pattern string, size uint64) (MMap, error) {
+	ans, err := os.CreateTemp(SHM_DIR, pattern)
+	if err != nil {
+		return nil, err
+	}
+	return file_mmap(ans, size, RDWR, true)
+}
+
+func Open(name string) (MMap, error) {
+	if !filepath.IsAbs(name) {
+		name = filepath.Join(SHM_DIR, name)
+	}
+	ans, err := os.OpenFile(name, os.O_RDONLY, 0)
+	if err != nil {
+		return nil, err
+	}
+	s, err := os.Stat(name)
+	if err != nil {
+		ans.Close()
+		return nil, err
+	}
+	return file_mmap(ans, uint64(s.Size()), READ, false)
+}