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Image.applyLayer: Be better at creating identical files

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There are some changes here that make the file metadata better match
the layer files:

* Set the mode of the file after the chown, as otherwise the per-group/uid
  specific flags and e.g. sticky bit is lost
* Use lchown instead of chown
* Delay mtime updates to after all other changes so that later file
  creation doesn't change the mtime for the parent directory
* Use Futimes in combination with O_PATH|O_NOFOLLOW to set mtime on symlinks
This commit is contained in:
Alexander Larsson 2013-09-13 15:45:58 +02:00 • committed by Tianon Gravi
parent 727e7fccca
commit 5d2ace3424
1 changed files with 43 additions and 12 deletions
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55
image.go
View file

@ -175,7 +175,13 @@ func (image *Image) TarLayer(compression Compression) (Archive, error) {
return Tar(layerPath, compression)
}
type TimeUpdate struct {
path string
time []syscall.Timeval
}
func (image *Image) applyLayer(layer, target string) error {
var updateTimes []TimeUpdate
oldmask := syscall.Umask(0)
defer syscall.Umask(oldmask)
err := filepath.Walk(layer, func(srcPath string, f os.FileInfo, err error) error {
@ -249,11 +255,6 @@ func (image *Image) applyLayer(layer, target string) error {
if err != nil {
return err
}
} else if srcStat.Mode&07777 != targetStat.Mode&07777 {
err = syscall.Chmod(targetPath, srcStat.Mode&07777)
if err != nil {
return err
}
}
} else if srcStat.Mode&syscall.S_IFLNK == syscall.S_IFLNK {
// Source is symlink
@ -293,22 +294,52 @@ func (image *Image) applyLayer(layer, target string) error {
return fmt.Errorf("Unknown type for file %s", srcPath)
}
err = syscall.Lchown(targetPath, int(srcStat.Uid), int(srcStat.Gid))
if err != nil {
return err
}
if srcStat.Mode&syscall.S_IFLNK != syscall.S_IFLNK {
err = syscall.Chown(targetPath, int(srcStat.Uid), int(srcStat.Gid))
err = syscall.Chmod(targetPath, srcStat.Mode&07777)
if err != nil {
return err
}
ts := []syscall.Timeval{
syscall.NsecToTimeval(srcStat.Atim.Nano()),
syscall.NsecToTimeval(srcStat.Mtim.Nano()),
}
syscall.Utimes(targetPath, ts)
}
ts := []syscall.Timeval{
syscall.NsecToTimeval(srcStat.Atim.Nano()),
syscall.NsecToTimeval(srcStat.Mtim.Nano()),
}
u := TimeUpdate {
path: targetPath,
time: ts,
}
// Delay time updates until all other changes done, or it is
// overwritten for directories (by child changes)
updateTimes = append(updateTimes, u)
}
return nil
})
return err
if err != nil {
return err
}
// We do this in reverse order so that children are updated before parents
for i := len(updateTimes) - 1; i >= 0; i-- {
update := updateTimes[i]
O_PATH := 010000000 // Not in syscall yet
fd, err := syscall.Open(update.path, syscall.O_RDWR | O_PATH | syscall.O_NOFOLLOW, 0600)
if err != nil {
return err
}
syscall.Futimes(fd, update.time)
_ = syscall.Close(fd)
}
return nil
}
func (image *Image) ensureImageDevice(devices DeviceSet) error {