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Fix change detection when applying tar layers

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The default gnu tar format has no sub-second precision mtime support,
and the golang tar writer currently doesn't support that either.
This means if we export the changes from a container we will not
get zeron in the sub-second precision field when the change is applied.

This means we can't compare that to the original without getting a
spurious change. So, we detect this case by treating a case where the
seconds match and either of the two nanoseconds are zero as equal.
This commit is contained in:
Alexander Larsson 2013-12-13 15:46:41 +01:00
parent 818c249bae
commit 10cd902f90
1 changed files with 18 additions and 2 deletions
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20
archive/changes.go
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@ -6,6 +6,7 @@ import (
"path/filepath" "path/filepath"
"strings" "strings"
"syscall" "syscall"
"time"
) )
type ChangeType int type ChangeType int
@ -34,6 +35,21 @@ func (change *Change) String() string {
return fmt.Sprintf("%s %s", kind, change.Path) return fmt.Sprintf("%s %s", kind, change.Path)
} }
// Gnu tar and the go tar writer don't have sub-second mtime
// precision, which is problematic when we apply changes via tar
// files, we handle this by comparing for exact times, *or* same
// second count and either a or b having exactly 0 nanoseconds
func sameFsTime(a, b time.Time) bool {
return a == b ||
(a.Unix() == b.Unix() &&
(a.Nanosecond() == 0 || b.Nanosecond() == 0))
}
func sameFsTimeSpec(a, b syscall.Timespec) bool {
return a.Sec == b.Sec &&
(a.Nsec == b.Nsec || a.Nsec == 0 || b.Nsec == 0)
}
func Changes(layers []string, rw string) ([]Change, error) { func Changes(layers []string, rw string) ([]Change, error) {
var changes []Change var changes []Change
err := filepath.Walk(rw, func(path string, f os.FileInfo, err error) error { err := filepath.Walk(rw, func(path string, f os.FileInfo, err error) error {
@ -85,7 +101,7 @@ func Changes(layers []string, rw string) ([]Change, error) {
// However, if it's a directory, maybe it wasn't actually modified. // 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 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 stat.IsDir() && f.IsDir() {
if f.Size() == stat.Size() && f.Mode() == stat.Mode() && f.ModTime() == stat.ModTime() { if f.Size() == stat.Size() && f.Mode() == stat.Mode() && sameFsTime(f.ModTime(), stat.ModTime()) {
// Both directories are the same, don't record the change // Both directories are the same, don't record the change
return nil return nil
} }
@ -181,7 +197,7 @@ func (info *FileInfo) addChanges(oldInfo *FileInfo, changes *[]Change) {
oldStat.Rdev != newStat.Rdev || oldStat.Rdev != newStat.Rdev ||
// Don't look at size for dirs, its not a good measure of change // Don't look at size for dirs, its not a good measure of change
(oldStat.Size != newStat.Size && oldStat.Mode&syscall.S_IFDIR != syscall.S_IFDIR) || (oldStat.Size != newStat.Size && oldStat.Mode&syscall.S_IFDIR != syscall.S_IFDIR) ||
getLastModification(oldStat) != getLastModification(newStat) { !sameFsTimeSpec(getLastModification(oldStat), getLastModification(newStat)) {
change := Change{ change := Change{
Path: newChild.path(), Path: newChild.path(),
Kind: ChangeModify, Kind: ChangeModify,