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Fix overlay2 busy error on mount

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When mounting overlays which have children, enforce that
the mount is always performed as read only. Newer versions
of the kernel return a device busy error when a lower directory
is in use as an upper directory in another overlay mount.

Adds committed file to indicate when an overlay is being used
as a parent, ensuring it will no longer be mounted with an
upper directory.

Signed-off-by: Derek McGowan <derek@mcgstyle.net>
This commit is contained in:
Derek McGowan 2019-08-21 15:03:52 -07:00
parent 0537236e5a
commit 477bf1e413
No known key found for this signature in database
GPG key ID: F58C5D0A4405ACDB
1 changed files with 29 additions and 6 deletions
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35
daemon/graphdriver/overlay2/overlay.go
View file

@ -446,6 +446,10 @@ func (d *Driver) create(id, parent string, opts *graphdriver.CreateOpts) (retErr
return err
}
if err := ioutil.WriteFile(path.Join(d.dir(parent), "committed"), []byte{}, 0600); err != nil {
return err
}
lower, err := d.getLower(parent)
if err != nil {
return err
@ -592,7 +596,20 @@ func (d *Driver) Get(id, mountLabel string) (_ containerfs.ContainerFS, retErr e
for i, s := range splitLowers {
absLowers[i] = path.Join(d.home, s)
}
opts := indexOff + "lowerdir=" + strings.Join(absLowers, ":") + ",upperdir=" + diffDir + ",workdir=" + workDir
var readonly bool
if _, err := os.Stat(path.Join(dir, "committed")); err == nil {
readonly = true
} else if !os.IsNotExist(err) {
return nil, err
}
var opts string
if readonly {
opts = indexOff + "lowerdir=" + diffDir + ":" + strings.Join(absLowers, ":")
} else {
opts = indexOff + "lowerdir=" + strings.Join(absLowers, ":") + ",upperdir=" + diffDir + ",workdir=" + workDir
}
mountData := label.FormatMountLabel(opts, mountLabel)
mount := unix.Mount
mountTarget := mergedDir
@ -612,7 +629,11 @@ func (d *Driver) Get(id, mountLabel string) (_ containerfs.ContainerFS, retErr e
// fit within a page and relative links make the mount data much
// smaller at the expense of requiring a fork exec to chroot.
if len(mountData) > pageSize {
opts = indexOff + "lowerdir=" + string(lowers) + ",upperdir=" + path.Join(id, diffDirName) + ",workdir=" + path.Join(id, workDirName)
if readonly {
opts = indexOff + "lowerdir=" + path.Join(id, diffDirName) + ":" + string(lowers)
} else {
opts = indexOff + "lowerdir=" + string(lowers) + ",upperdir=" + path.Join(id, diffDirName) + ",workdir=" + path.Join(id, workDirName)
}
mountData = label.FormatMountLabel(opts, mountLabel)
if len(mountData) > pageSize {
return nil, fmt.Errorf("cannot mount layer, mount label too large %d", len(mountData))
@ -628,10 +649,12 @@ func (d *Driver) Get(id, mountLabel string) (_ containerfs.ContainerFS, retErr e
return nil, fmt.Errorf("error creating overlay mount to %s: %v", mergedDir, err)
}
// chown "workdir/work" to the remapped root UID/GID. Overlay fs inside a
// user namespace requires this to move a directory from lower to upper.
if err := os.Chown(path.Join(workDir, workDirName), rootUID, rootGID); err != nil {
return nil, err
if !readonly {
// chown "workdir/work" to the remapped root UID/GID. Overlay fs inside a
// user namespace requires this to move a directory from lower to upper.
if err := os.Chown(path.Join(workDir, workDirName), rootUID, rootGID); err != nil {
return nil, err
}
}
return containerfs.NewLocalContainerFS(mergedDir), nil