Add fs package

Add diff comparison with support for double walking
two trees for comparison or single walking a diff
tree. Single walking requires further implementation
for specific mount types.

Add directory copy function which is intended to provide
fastest possible local copy of file system directories
without hardlinking.

Add test package to make creating filesystems for
test easy and comparisons deep and informative.

Signed-off-by: Derek McGowan <derek@mcgstyle.net> (github: dmcgowan)

fs/copy_linux.go

@@ -0,0 +1,110 @@
+package fs
+
+import (
+	"io"
+	"os"
+	"strconv"
+	"syscall"
+
+	"github.com/pkg/errors"
+	"github.com/stevvooe/continuity/sysx"
+)
+
+var (
+	kernel, major int
+)
+
+func init() {
+	uts := &syscall.Utsname{}
+
+	err := syscall.Uname(uts)
+	if err != nil {
+		panic(err)
+	}
+
+	p := [2][]byte{{}, {}}
+
+	release := uts.Release
+	i := 0
+	for pi := 0; pi < len(p); pi++ {
+		for release[i] != 0 {
+			c := byte(release[i])
+			i++
+			if c == '.' || c == '-' {
+				break
+			}
+			p[pi] = append(p[pi], c)
+		}
+	}
+	kernel, err = strconv.Atoi(string(p[0]))
+	if err != nil {
+		panic(err)
+	}
+	major, err = strconv.Atoi(string(p[1]))
+	if err != nil {
+		panic(err)
+	}
+}
+
+func copyFileInfo(fi os.FileInfo, name string) error {
+	st := fi.Sys().(*syscall.Stat_t)
+	if err := os.Lchown(name, int(st.Uid), int(st.Gid)); err != nil {
+		return errors.Wrapf(err, "failed to chown %s", name)
+	}
+
+	if (fi.Mode() & os.ModeSymlink) != os.ModeSymlink {
+		if err := os.Chmod(name, fi.Mode()); err != nil {
+			return errors.Wrapf(err, "failed to chmod %s", name)
+		}
+	}
+
+	if err := syscall.UtimesNano(name, []syscall.Timespec{st.Atim, st.Mtim}); err != nil {
+		return errors.Wrapf(err, "failed to utime %s", name)
+	}
+
+	return nil
+}
+
+func copyFileContent(dst, src *os.File) error {
+	if checkKernel(4, 5) {
+		// Use copy_file_range to do in kernel copying
+		// See https://lwn.net/Articles/659523/
+		// 326 on x86_64
+		st, err := src.Stat()
+		if err != nil {
+			return errors.Wrap(err, "unable to stat source")
+		}
+		n, _, e1 := syscall.Syscall6(326, src.Fd(), 0, dst.Fd(), 0, uintptr(st.Size()), 0)
+		if e1 != 0 {
+			return errors.Wrap(err, "copy_file_range failed")
+		}
+		if int64(n) != st.Size() {
+			return errors.Wrapf(err, "short copy: %d of %d", int64(n), st.Size())
+		}
+		return nil
+	}
+	_, err := io.Copy(dst, src)
+	return err
+}
+
+func checkKernel(k, m int) bool {
+	return (kernel == k && major >= m) || kernel > k
+}
+
+func copyXAttrs(dst, src string) error {
+	xattrKeys, err := sysx.LListxattr(src)
+	if err != nil {
+		return errors.Wrapf(err, "failed to list xattrs on %s", src)
+	}
+	for _, xattr := range xattrKeys {
+		data, err := sysx.LGetxattr(src, xattr)
+		if err != nil {
+			return errors.Wrapf(err, "failed to get xattr %q on %s", xattr, src)
+		}
+		if err := sysx.LSetxattr(dst, xattr, data, 0); err != nil {
+			return errors.Wrapf(err, "failed to set xattr %q on %s", xattr, dst)
+		}
+	}
+
+	return nil
+}