containerd/fs/diff.go

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package fs
import (
"context"
"os"
"path/filepath"
"strings"
"golang.org/x/sync/errgroup"
"github.com/Sirupsen/logrus"
)
// ChangeKind is the type of modification that
// a change is making.
type ChangeKind int
const (
// ChangeKindAdd represents an addition of
// a file
ChangeKindAdd = iota
// ChangeKindModify represents a change to
// an existing file
ChangeKindModify
// ChangeKindDelete represents a delete of
// a file
ChangeKindDelete
)
func (k ChangeKind) String() string {
switch k {
case ChangeKindAdd:
return "add"
case ChangeKindModify:
return "modify"
case ChangeKindDelete:
return "delete"
default:
return ""
}
}
// Change represents single change between a diff and its parent.
type Change struct {
Kind ChangeKind
Path string
}
// ChangeFunc is the type of function called for each change
// computed during a directory changes calculation.
type ChangeFunc func(ChangeKind, string, os.FileInfo, error) error
// Changes computes changes between two directories calling the
// given change function for each computed change. The first
// directory is intended to the base directory and second
// directory the changed directory.
//
// The change callback is called by the order of path names and
// should be appliable in that order.
// Due to this apply ordering, the following is true
// - Removed directory trees only create a single change for the root
// directory removed. Remaining changes are implied.
// - A directory which is modified to become a file will not have
// delete entries for sub-path items, their removal is implied
// by the removal of the parent directory.
//
// Opaque directories will not be treated specially and each file
// removed from the base directory will show up as a removal.
//
// File content comparisons will be done on files which have timestamps
// which may have been truncated. If either of the files being compared
// has a zero value nanosecond value, each byte will be compared for
// differences. If 2 files have the same seconds value but different
// nanosecond values where one of those values is zero, the files will
// be considered unchanged if the content is the same. This behavior
// is to account for timestamp truncation during archiving.
func Changes(ctx context.Context, a, b string, changeFn ChangeFunc) error {
if a == "" {
logrus.Debugf("Using single walk diff for %s", b)
return addDirChanges(ctx, changeFn, b)
} else if diffOptions := detectDirDiff(b, a); diffOptions != nil {
logrus.Debugf("Using single walk diff for %s from %s", diffOptions.diffDir, a)
return diffDirChanges(ctx, changeFn, a, diffOptions)
}
logrus.Debugf("Using double walk diff for %s from %s", b, a)
return doubleWalkDiff(ctx, changeFn, a, b)
}
func addDirChanges(ctx context.Context, changeFn ChangeFunc, root string) error {
return filepath.Walk(root, func(path string, f os.FileInfo, err error) error {
if err != nil {
return err
}
// Rebase path
path, err = filepath.Rel(root, path)
if err != nil {
return err
}
path = filepath.Join(string(os.PathSeparator), path)
// Skip root
if path == string(os.PathSeparator) {
return nil
}
return changeFn(ChangeKindAdd, path, f, nil)
})
}
// diffDirOptions is used when the diff can be directly calculated from
// a diff directory to its base, without walking both trees.
type diffDirOptions struct {
diffDir string
skipChange func(string) (bool, error)
deleteChange func(string, string, os.FileInfo) (string, error)
}
// diffDirChanges walks the diff directory and compares changes against the base.
func diffDirChanges(ctx context.Context, changeFn ChangeFunc, base string, o *diffDirOptions) error {
changedDirs := make(map[string]struct{})
return filepath.Walk(o.diffDir, func(path string, f os.FileInfo, err error) error {
if err != nil {
return err
}
// Rebase path
path, err = filepath.Rel(o.diffDir, path)
if err != nil {
return err
}
path = filepath.Join(string(os.PathSeparator), path)
// Skip root
if path == string(os.PathSeparator) {
return nil
}
// TODO: handle opaqueness, start new double walker at this
// location to get deletes, and skip tree in single walker
if o.skipChange != nil {
if skip, err := o.skipChange(path); skip {
return err
}
}
var kind ChangeKind
deletedFile, err := o.deleteChange(o.diffDir, path, f)
if err != nil {
return err
}
// Find out what kind of modification happened
if deletedFile != "" {
path = deletedFile
kind = ChangeKindDelete
f = nil
} else {
// Otherwise, the file was added
kind = ChangeKindAdd
// ...Unless it already existed in a base, in which case, it's a modification
stat, err := os.Stat(filepath.Join(base, path))
if err != nil && !os.IsNotExist(err) {
return err
}
if err == nil {
// The file existed in the base, so that's a modification
// However, if it's a directory, maybe it wasn't actually modified.
// If you modify /foo/bar/baz, then /foo will be part of the changed files only because it's the parent of bar
if stat.IsDir() && f.IsDir() {
if f.Size() == stat.Size() && f.Mode() == stat.Mode() && sameFsTime(f.ModTime(), stat.ModTime()) {
// Both directories are the same, don't record the change
return nil
}
}
kind = ChangeKindModify
}
}
// If /foo/bar/file.txt is modified, then /foo/bar must be part of the changed files.
// This block is here to ensure the change is recorded even if the
// modify time, mode and size of the parent directory in the rw and ro layers are all equal.
// Check https://github.com/docker/docker/pull/13590 for details.
if f.IsDir() {
changedDirs[path] = struct{}{}
}
if kind == ChangeKindAdd || kind == ChangeKindDelete {
parent := filepath.Dir(path)
if _, ok := changedDirs[parent]; !ok && parent != "/" {
pi, err := os.Stat(filepath.Join(o.diffDir, parent))
if err := changeFn(ChangeKindModify, parent, pi, err); err != nil {
return err
}
changedDirs[parent] = struct{}{}
}
}
return changeFn(kind, path, f, nil)
})
}
// doubleWalkDiff walks both directories to create a diff
func doubleWalkDiff(ctx context.Context, changeFn ChangeFunc, a, b string) (err error) {
g, ctx := errgroup.WithContext(ctx)
var (
c1 = make(chan *currentPath)
c2 = make(chan *currentPath)
f1, f2 *currentPath
rmdir string
)
g.Go(func() error {
defer close(c1)
return pathWalk(ctx, a, c1)
})
g.Go(func() error {
defer close(c2)
return pathWalk(ctx, b, c2)
})
g.Go(func() error {
for c1 != nil || c2 != nil {
if f1 == nil && c1 != nil {
f1, err = nextPath(ctx, c1)
if err != nil {
return err
}
if f1 == nil {
c1 = nil
}
}
if f2 == nil && c2 != nil {
f2, err = nextPath(ctx, c2)
if err != nil {
return err
}
if f2 == nil {
c2 = nil
}
}
if f1 == nil && f2 == nil {
continue
}
var f os.FileInfo
k, p := pathChange(f1, f2)
switch k {
case ChangeKindAdd:
if rmdir != "" {
rmdir = ""
}
f = f2.f
f2 = nil
case ChangeKindDelete:
// Check if this file is already removed by being
// under of a removed directory
if rmdir != "" && strings.HasPrefix(f1.path, rmdir) {
f1 = nil
continue
} else if rmdir == "" && f1.f.IsDir() {
rmdir = f1.path + string(os.PathSeparator)
} else if rmdir != "" {
rmdir = ""
}
f1 = nil
case ChangeKindModify:
same, err := sameFile(f1, f2)
if err != nil {
return err
}
if f1.f.IsDir() && !f2.f.IsDir() {
rmdir = f1.path + string(os.PathSeparator)
} else if rmdir != "" {
rmdir = ""
}
f = f2.f
f1 = nil
f2 = nil
if same {
continue
}
}
if err := changeFn(k, p, f, nil); err != nil {
return err
}
}
return nil
})
return g.Wait()
}