daa3a7665e
This is necessary so we can mount snapshots more than once with overlayfs, otherwise mounts enter an unknown state. related: https://github.com/moby/buildkit/pull/1100 Signed-off-by: Laura Brehm <laurabrehm@hey.com> Co-authored-by: Zou Nengren <zouyee1989@gmail.com>
122 lines
3.5 KiB
Go
122 lines
3.5 KiB
Go
/*
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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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"fmt"
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"strings"
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"github.com/containerd/continuity/fs"
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)
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// Mount is the lingua franca of containerd. A mount represents a
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// serialized mount syscall. Components either emit or consume mounts.
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type Mount struct {
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// Type specifies the host-specific of the mount.
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Type string
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// Source specifies where to mount from. Depending on the host system, this
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// can be a source path or device.
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Source string
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// Target specifies an optional subdirectory as a mountpoint. It assumes that
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// the subdirectory exists in a parent mount.
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Target string
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// Options contains zero or more fstab-style mount options. Typically,
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// these are platform specific.
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Options []string
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}
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// All mounts all the provided mounts to the provided target. If submounts are
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// present, it assumes that parent mounts come before child mounts.
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func All(mounts []Mount, target string) error {
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for _, m := range mounts {
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if err := m.Mount(target); err != nil {
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return err
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}
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}
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return nil
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}
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// UnmountMounts unmounts all the mounts under a target in the reverse order of
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// the mounts array provided.
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func UnmountMounts(mounts []Mount, target string, flags int) error {
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for i := len(mounts) - 1; i >= 0; i-- {
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mountpoint, err := fs.RootPath(target, mounts[i].Target)
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if err != nil {
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return err
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}
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if err := UnmountAll(mountpoint, flags); err != nil {
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if i == len(mounts)-1 { // last mount
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return err
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}
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}
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}
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return nil
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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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target, err := fs.RootPath(target, m.Target)
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if err != nil {
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return fmt.Errorf("failed to join path %q with root %q: %w", m.Target, target, err)
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}
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return m.mount(target)
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}
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// readonlyMounts modifies the received mount options
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// to make them readonly
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func readonlyMounts(mounts []Mount) []Mount {
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for i, m := range mounts {
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if m.Type == "overlay" {
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mounts[i].Options = readonlyOverlay(m.Options)
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continue
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}
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opts := make([]string, 0, len(m.Options))
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for _, opt := range m.Options {
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if opt != "rw" && opt != "ro" { // skip `ro` too so we don't append it twice
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opts = append(opts, opt)
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}
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}
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opts = append(opts, "ro")
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mounts[i].Options = opts
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}
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return mounts
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}
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// readonlyOverlay takes mount options for overlay mounts and makes them readonly by
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// removing workdir and upperdir (and appending the upperdir layer to lowerdir) - see:
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// https://www.kernel.org/doc/html/latest/filesystems/overlayfs.html#multiple-lower-layers
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func readonlyOverlay(opt []string) []string {
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out := make([]string, 0, len(opt))
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upper := ""
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for _, o := range opt {
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if strings.HasPrefix(o, "upperdir=") {
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upper = strings.TrimPrefix(o, "upperdir=")
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} else if !strings.HasPrefix(o, "workdir=") {
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out = append(out, o)
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}
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}
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if upper != "" {
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for i, o := range out {
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if strings.HasPrefix(o, "lowerdir=") {
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out[i] = "lowerdir=" + upper + ":" + strings.TrimPrefix(o, "lowerdir=")
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}
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}
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}
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return out
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}
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