From b83bd45dfbc258d5cf06939faba61775e075b08d Mon Sep 17 00:00:00 2001 From: Giuseppe Scrivano Date: Wed, 13 Sep 2023 15:36:27 +0200 Subject: [PATCH] overlay, composefs: use data-only lower layers use the new overlay data-only feature to mount the composefs data directory so there is no need for upper layers to create whiteouts to hide payload files. The feature was added to Linux 6.5. Signed-off-by: Giuseppe Scrivano --- drivers/overlay/check.go | 33 ++++++++++++++++++++++++++++ drivers/overlay/mount.go | 17 +++++++++++++-- drivers/overlay/overlay.go | 44 ++++++++++++++++++++++++++++++++------ 3 files changed, 85 insertions(+), 9 deletions(-) diff --git a/drivers/overlay/check.go b/drivers/overlay/check.go index 60980994b2..d8139f6566 100644 --- a/drivers/overlay/check.go +++ b/drivers/overlay/check.go @@ -275,3 +275,36 @@ func supportsIdmappedLowerLayers(home string) (bool, error) { }() return true, nil } + +// supportsDataOnlyLayers checks if the kernel supports mounting a overlay file system +// that uses data-only layers. +func supportsDataOnlyLayers(home string) (bool, error) { + layerDir, err := os.MkdirTemp(home, "compat") + if err != nil { + return false, err + } + defer func() { + _ = os.RemoveAll(layerDir) + }() + + mergedDir := filepath.Join(layerDir, "merged") + lowerDir := filepath.Join(layerDir, "lower") + lowerDirDataOnly := filepath.Join(layerDir, "lower-data") + upperDir := filepath.Join(layerDir, "upper") + workDir := filepath.Join(layerDir, "work") + + _ = idtools.MkdirAs(mergedDir, 0o700, 0, 0) + _ = idtools.MkdirAs(lowerDir, 0o700, 0, 0) + _ = idtools.MkdirAs(lowerDirDataOnly, 0o700, 0, 0) + _ = idtools.MkdirAs(upperDir, 0o700, 0, 0) + _ = idtools.MkdirAs(workDir, 0o700, 0, 0) + + opts := fmt.Sprintf("lowerdir=%s::%s,upperdir=%s,workdir=%s,metacopy=on", lowerDir, lowerDirDataOnly, upperDir, workDir) + flags := uintptr(0) + if err := unix.Mount("overlay", mergedDir, "overlay", flags, opts); err != nil { + return false, err + } + _ = unix.Unmount(mergedDir, unix.MNT_DETACH) + + return true, nil +} diff --git a/drivers/overlay/mount.go b/drivers/overlay/mount.go index 33e60b1189..bc052f33b4 100644 --- a/drivers/overlay/mount.go +++ b/drivers/overlay/mount.go @@ -141,14 +141,27 @@ func mountOverlayFromMain() { // the new value for the list of lowers, because it's shorter. if lowerv != "" { lowers := strings.Split(lowerv, ":") + var newLowers []string + dataOnly := false for i := range lowers { + if lowers[i] == "" { + dataOnly = true + continue + } lowerFd, err := unix.Open(lowers[i], unix.O_RDONLY, 0) if err != nil { fatal(err) } - lowers[i] = fmt.Sprintf("%d", lowerFd) + var lower string + if dataOnly { + lower = fmt.Sprintf(":%d", lowerFd) + dataOnly = false + } else { + lower = fmt.Sprintf("%d", lowerFd) + } + newLowers = append(newLowers, lower) } - lowerv = strings.Join(lowers, ":") + lowerv = strings.Join(newLowers, ":") } // Reconstruct the Label field. diff --git a/drivers/overlay/overlay.go b/drivers/overlay/overlay.go index 91ca273de0..0663e325f3 100644 --- a/drivers/overlay/overlay.go +++ b/drivers/overlay/overlay.go @@ -1657,8 +1657,6 @@ func (d *Driver) get(id string, disableShifting bool, options graphdriver.MountO optsList = append(optsList, "metacopy=on", "redirect_dir=on") } - absLowers = append(absLowers, composeFsLayers...) - if len(absLowers) == 0 { absLowers = append(absLowers, path.Join(dir, "empty")) } @@ -1752,11 +1750,20 @@ func (d *Driver) get(id string, disableShifting bool, options graphdriver.MountO absLowers = newAbsDir } + lowerDirs := strings.Join(absLowers, ":") + if len(composeFsLayers) > 0 { + composeFsLayersLowerDirs := strings.Join(composeFsLayers, "::") + lowerDirs = lowerDirs + "::" + composeFsLayersLowerDirs + } + // absLowers is not valid anymore now as we have added composeFsLayers to it, so prevent + // its usage. + absLowers = nil + var opts string if readWrite { - opts = fmt.Sprintf("lowerdir=%s,upperdir=%s,workdir=%s", strings.Join(absLowers, ":"), diffDir, workdir) + opts = fmt.Sprintf("lowerdir=%s,upperdir=%s,workdir=%s", lowerDirs, diffDir, workdir) } else { - opts = fmt.Sprintf("lowerdir=%s:%s", diffDir, strings.Join(absLowers, ":")) + opts = fmt.Sprintf("lowerdir=%s:%s", diffDir, lowerDirs) } if len(optsList) > 0 { opts = fmt.Sprintf("%s,%s", opts, strings.Join(optsList, ",")) @@ -1800,9 +1807,9 @@ func (d *Driver) get(id string, disableShifting bool, options graphdriver.MountO if readWrite { diffDir := path.Join(id, "diff") workDir := path.Join(id, "work") - opts = fmt.Sprintf("lowerdir=%s,upperdir=%s,workdir=%s", strings.Join(absLowers, ":"), diffDir, workDir) + opts = fmt.Sprintf("lowerdir=%s,upperdir=%s,workdir=%s", lowerDirs, diffDir, workDir) } else { - opts = fmt.Sprintf("lowerdir=%s:%s", diffDir, strings.Join(absLowers, ":")) + opts = fmt.Sprintf("lowerdir=%s:%s", diffDir, lowerDirs) } if len(optsList) > 0 { opts = strings.Join(append([]string{opts}, optsList...), ",") @@ -2009,11 +2016,34 @@ func (d *Driver) CleanupStagingDirectory(stagingDirectory string) error { return os.RemoveAll(stagingDirectory) } +func (d *Driver) supportsDataOnlyLayers() (bool, error) { + feature := "dataonly-layers" + overlayCacheResult, overlayCacheText, err := cachedFeatureCheck(d.runhome, feature) + if err == nil { + if overlayCacheResult { + logrus.Debugf("Cached value indicated that data-only layers for overlay are supported") + return true, nil + } + logrus.Debugf("Cached value indicated that data-only layers for overlay are not supported") + return false, errors.New(overlayCacheText) + } + supportsDataOnly, err := supportsDataOnlyLayers(d.home) + if err2 := cachedFeatureRecord(d.runhome, feature, supportsDataOnly, ""); err2 != nil { + return false, fmt.Errorf("recording overlay data-only layers support status: %w", err2) + } + return supportsDataOnly, err +} + func (d *Driver) useComposeFs() bool { if !composeFsSupported() || unshare.IsRootless() { return false } - return true + supportsDataOnlyLayers, err := d.supportsDataOnlyLayers() + if err != nil { + logrus.Debugf("Check for data-only layers failed with: %v", err) + return true + } + return supportsDataOnlyLayers } // ApplyDiff applies the changes in the new layer using the specified function