os, syscall: implement Stat and Lstat

File.Stat is left as a stub for now.

Tests are a bit stubbed down because os.ReadDir, os.Symlink, and t.TempDir are not yet (fully) implemented.
TODO: reimport tests from upstream as those materialize.

src/os/stat_linux.go

@@ -0,0 +1,53 @@
+// +build linux,!baremetal
+
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package os
+
+import (
+	"syscall"
+	"time"
+)
+
+func fillFileStatFromSys(fs *fileStat, name string) {
+	fs.name = basename(name)
+	fs.size = fs.sys.Size
+	fs.modTime = timespecToTime(fs.sys.Mtim)
+	fs.mode = FileMode(fs.sys.Mode & 0777)
+	switch fs.sys.Mode & syscall.S_IFMT {
+	case syscall.S_IFBLK:
+		fs.mode |= ModeDevice
+	case syscall.S_IFCHR:
+		fs.mode |= ModeDevice | ModeCharDevice
+	case syscall.S_IFDIR:
+		fs.mode |= ModeDir
+	case syscall.S_IFIFO:
+		fs.mode |= ModeNamedPipe
+	case syscall.S_IFLNK:
+		fs.mode |= ModeSymlink
+	case syscall.S_IFREG:
+		// nothing to do
+	case syscall.S_IFSOCK:
+		fs.mode |= ModeSocket
+	}
+	if fs.sys.Mode&syscall.S_ISGID != 0 {
+		fs.mode |= ModeSetgid
+	}
+	if fs.sys.Mode&syscall.S_ISUID != 0 {
+		fs.mode |= ModeSetuid
+	}
+	if fs.sys.Mode&syscall.S_ISVTX != 0 {
+		fs.mode |= ModeSticky
+	}
+}
+
+func timespecToTime(ts syscall.Timespec) time.Time {
+	return time.Unix(int64(ts.Sec), int64(ts.Nsec))
+}
+
+// For testing.
+func atime(fi FileInfo) time.Time {
+	return timespecToTime(fi.Sys().(*syscall.Stat_t).Atim)
+}