Support >= 128 layers in overlayfs snapshots
Auto-detect longest common dir in lowerdir option and compact it if the option size is hitting one page size. If does, Use chdir + CLONE to do mount thing to avoid hitting one page argument buffer in linux kernel mount. Signed-off-by: Wei Fu <fhfuwei@163.com>
This commit is contained in:
Wei Fu
@@ -17,16 +17,41 @@
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package mount
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import (
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"fmt"
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"os"
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"path"
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"strings"
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"time"
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"github.com/containerd/containerd/sys"
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"github.com/pkg/errors"
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"golang.org/x/sys/unix"
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)
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var pagesize = 4096
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func init() {
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pagesize = os.Getpagesize()
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}
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// Mount to the provided target path
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func (m *Mount) Mount(target string) error {
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flags, data := parseMountOptions(m.Options)
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var (
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chdir string
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options = m.Options
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)
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// avoid hitting one page limit of mount argument buffer
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//
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// NOTE: 512 is a buffer during pagesize check.
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if m.Type == "overlay" && optionsSize(options) >= pagesize-512 {
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chdir, options = compactLowerdirOption(options)
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}
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flags, data := parseMountOptions(options)
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if len(data) > pagesize {
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return errors.Errorf("mount options is too long")
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}
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// propagation types.
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const ptypes = unix.MS_SHARED | unix.MS_PRIVATE | unix.MS_SLAVE | unix.MS_UNBINDABLE
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@@ -38,7 +63,7 @@ func (m *Mount) Mount(target string) error {
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if flags&unix.MS_REMOUNT == 0 || data != "" {
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// Initial call applying all non-propagation flags for mount
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// or remount with changed data
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if err := unix.Mount(m.Source, target, m.Type, uintptr(oflags), data); err != nil {
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if err := mountAt(chdir, m.Source, target, m.Type, uintptr(oflags), data); err != nil {
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return err
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}
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}
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@@ -155,3 +180,129 @@ func parseMountOptions(options []string) (int, string) {
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}
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return flag, strings.Join(data, ",")
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}
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// compactLowerdirOption updates overlay lowdir option and returns the common
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// dir among all the lowdirs.
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func compactLowerdirOption(opts []string) (string, []string) {
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idx, dirs := findOverlayLowerdirs(opts)
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if idx == -1 || len(dirs) == 1 {
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// no need to compact if there is only one lowerdir
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return "", opts
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}
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// find out common dir
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commondir := longestCommonPrefix(dirs)
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if commondir == "" {
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return "", opts
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}
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// NOTE: the snapshot id is based on digits.
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// in order to avoid to get snapshots/x, should be back to parent dir.
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// however, there is assumption that the common dir is ${root}/io.containerd.v1.overlayfs/snapshots.
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commondir = path.Dir(commondir)
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if commondir == "/" {
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return "", opts
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}
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commondir = commondir + "/"
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newdirs := make([]string, 0, len(dirs))
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for _, dir := range dirs {
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newdirs = append(newdirs, dir[len(commondir):])
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}
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newopts := copyOptions(opts)
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newopts = append(newopts[:idx], newopts[idx+1:]...)
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newopts = append(newopts, fmt.Sprintf("lowerdir=%s", strings.Join(newdirs, ":")))
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return commondir, newopts
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}
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// findOverlayLowerdirs returns the index of lowerdir in mount's options and
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// all the lowerdir target.
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func findOverlayLowerdirs(opts []string) (int, []string) {
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var (
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idx = -1
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prefix = "lowerdir="
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)
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for i, opt := range opts {
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if strings.HasPrefix(opt, prefix) {
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idx = i
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break
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}
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}
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if idx == -1 {
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return -1, nil
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}
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return idx, strings.Split(opts[idx][len(prefix):], ":")
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}
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// longestCommonPrefix finds the longest common prefix in the string slice.
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func longestCommonPrefix(strs []string) string {
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if len(strs) == 0 {
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return ""
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} else if len(strs) == 1 {
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return strs[0]
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}
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// find out the min/max value by alphabetical order
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min, max := strs[0], strs[0]
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for _, str := range strs[1:] {
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if min > str {
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min = str
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}
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if max < str {
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max = str
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}
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}
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// find out the common part between min and max
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for i := 0; i < len(min) && i < len(max); i++ {
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if min[i] != max[i] {
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return min[:i]
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}
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}
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return min
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}
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// copyOptions copies the options.
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func copyOptions(opts []string) []string {
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if len(opts) == 0 {
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return nil
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}
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acopy := make([]string, len(opts))
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copy(acopy, opts)
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return acopy
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}
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// optionsSize returns the byte size of options of mount.
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func optionsSize(opts []string) int {
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size := 0
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for _, opt := range opts {
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size += len(opt)
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}
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return size
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}
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func mountAt(chdir string, source, target, fstype string, flags uintptr, data string) error {
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if chdir == "" {
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return unix.Mount(source, target, fstype, flags, data)
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}
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f, err := os.Open(chdir)
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if err != nil {
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return errors.Wrap(err, "failed to mountat")
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}
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defer f.Close()
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fs, err := f.Stat()
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if err != nil {
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return errors.Wrap(err, "failed to mountat")
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}
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if !fs.IsDir() {
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return errors.Wrap(errors.Errorf("%s is not dir", chdir), "failed to mountat")
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}
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return errors.Wrap(sys.FMountat(f.Fd(), source, target, fstype, flags, data), "failed to mountat")
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}
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94
mount/mount_linux_test.go
Normal file
94
mount/mount_linux_test.go
Normal file
@@ -0,0 +1,94 @@
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// +build linux
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/*
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Copyright The containerd Authors.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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package mount
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import (
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"reflect"
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"testing"
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)
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func TestLongestCommonPrefix(t *testing.T) {
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tcases := []struct {
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in []string
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expected string
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}{
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{[]string{}, ""},
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{[]string{"foo"}, "foo"},
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{[]string{"foo", "bar"}, ""},
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{[]string{"foo", "foo"}, "foo"},
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{[]string{"foo", "foobar"}, "foo"},
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{[]string{"foo", "", "foobar"}, ""},
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}
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for i, tc := range tcases {
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if got := longestCommonPrefix(tc.in); got != tc.expected {
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t.Fatalf("[%d case] expected (%s), but got (%s)", i+1, tc.expected, got)
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}
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}
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}
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func TestCompactLowerdirOption(t *testing.T) {
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tcases := []struct {
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opts []string
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commondir string
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newopts []string
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}{
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// no lowerdir or only one
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{
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[]string{"workdir=a"},
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"",
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[]string{"workdir=a"},
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},
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{
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[]string{"workdir=a", "lowerdir=b"},
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"",
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[]string{"workdir=a", "lowerdir=b"},
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},
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// >= 2 lowerdir
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{
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[]string{"lowerdir=/snapshots/1/fs:/snapshots/10/fs"},
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"/snapshots/",
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[]string{"lowerdir=1/fs:10/fs"},
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},
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{
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[]string{"lowerdir=/snapshots/1/fs:/snapshots/10/fs:/snapshots/2/fs"},
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"/snapshots/",
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[]string{"lowerdir=1/fs:10/fs:2/fs"},
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},
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// if common dir is /
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{
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[]string{"lowerdir=/snapshots/1/fs:/other_snapshots/1/fs"},
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"",
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[]string{"lowerdir=/snapshots/1/fs:/other_snapshots/1/fs"},
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},
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}
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for i, tc := range tcases {
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dir, opts := compactLowerdirOption(tc.opts)
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if dir != tc.commondir {
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t.Fatalf("[%d case] expected common dir (%s), but got (%s)", i+1, tc.commondir, dir)
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}
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if !reflect.DeepEqual(opts, tc.newopts) {
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t.Fatalf("[%d case] expected options (%v), but got (%v)", i+1, tc.newopts, opts)
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}
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}
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}
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