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package container
import (
"encoding/gob"
"fmt"
"os"
"path/filepath"
"slices"
"strings"
. "syscall"
)
const (
// intermediate root file name pattern for [MountOverlayOp.Upper];
// remains after apply returns
intermediatePatternOverlayUpper = "overlay.upper.*"
// intermediate root file name pattern for [MountOverlayOp.Work];
// remains after apply returns
intermediatePatternOverlayWork = "overlay.work.*"
)
func init() { gob.Register(new(MountOverlayOp)) }
// Overlay appends an [Op] that mounts the overlay pseudo filesystem on [MountOverlayOp.Target].
func (f *Ops) Overlay(target, state, work *Absolute, layers ...*Absolute) *Ops {
*f = append(*f, &MountOverlayOp{
Target: target,
Lower: layers,
Upper: state,
Work: work,
})
return f
}
// OverlayEphemeral appends an [Op] that mounts the overlay pseudo filesystem on [MountOverlayOp.Target]
// with an ephemeral upperdir and workdir.
func (f *Ops) OverlayEphemeral(target *Absolute, layers ...*Absolute) *Ops {
return f.Overlay(target, AbsFHSRoot, nil, layers...)
}
// OverlayReadonly appends an [Op] that mounts the overlay pseudo filesystem readonly on [MountOverlayOp.Target]
func (f *Ops) OverlayReadonly(target *Absolute, layers ...*Absolute) *Ops {
return f.Overlay(target, nil, nil, layers...)
}
// MountOverlayOp mounts [FstypeOverlay] on container path Target.
type MountOverlayOp struct {
Target *Absolute
// Any filesystem, does not need to be on a writable filesystem.
Lower []*Absolute
// formatted for [OptionOverlayLowerdir], resolved, prefixed and escaped during early
lower []string
// The upperdir is normally on a writable filesystem.
//
// If Work is nil and Upper holds the special value [FHSRoot],
// an ephemeral upperdir and workdir will be set up.
//
// If both Work and Upper are empty strings, upperdir and workdir is omitted and the overlay is mounted readonly.
Upper *Absolute
// formatted for [OptionOverlayUpperdir], resolved, prefixed and escaped during early
upper string
// The workdir needs to be an empty directory on the same filesystem as upperdir.
Work *Absolute
// formatted for [OptionOverlayWorkdir], resolved, prefixed and escaped during early
work string
ephemeral bool
}
func (o *MountOverlayOp) early(*setupState) error {
if o.Work == nil && o.Upper != nil {
switch o.Upper.String() {
case FHSRoot: // ephemeral
o.ephemeral = true // intermediate root not yet available
default:
return msg.WrapErr(EINVAL, fmt.Sprintf("upperdir has unexpected value %q", o.Upper))
}
}
// readonly handled in apply
if !o.ephemeral {
if o.Upper != o.Work && (o.Upper == nil || o.Work == nil) {
// unreachable
return msg.WrapErr(ENOTRECOVERABLE, "impossible overlay state reached")
}
if o.Upper != nil {
if v, err := filepath.EvalSymlinks(o.Upper.String()); err != nil {
return wrapErrSelf(err)
} else {
o.upper = EscapeOverlayDataSegment(toHost(v))
}
}
if o.Work != nil {
if v, err := filepath.EvalSymlinks(o.Work.String()); err != nil {
return wrapErrSelf(err)
} else {
o.work = EscapeOverlayDataSegment(toHost(v))
}
}
}
o.lower = make([]string, len(o.Lower))
for i, a := range o.Lower {
if a == nil {
return EBADE
}
if v, err := filepath.EvalSymlinks(a.String()); err != nil {
return wrapErrSelf(err)
} else {
o.lower[i] = EscapeOverlayDataSegment(toHost(v))
}
}
return nil
}
func (o *MountOverlayOp) apply(state *setupState) error {
if o.Target == nil {
return EBADE
}
target := toSysroot(o.Target.String())
if err := os.MkdirAll(target, state.ParentPerm); err != nil {
return wrapErrSelf(err)
}
if o.ephemeral {
var err error
// these directories are created internally, therefore early (absolute, symlink, prefix, escape) is bypassed
if o.upper, err = os.MkdirTemp(FHSRoot, intermediatePatternOverlayUpper); err != nil {
return wrapErrSelf(err)
}
if o.work, err = os.MkdirTemp(FHSRoot, intermediatePatternOverlayWork); err != nil {
return wrapErrSelf(err)
}
}
options := make([]string, 0, 4)
if o.upper == zeroString && o.work == zeroString { // readonly
if len(o.Lower) < 2 {
return msg.WrapErr(EINVAL, "readonly overlay requires at least two lowerdir")
}
// "upperdir=" and "workdir=" may be omitted. In that case the overlay will be read-only
} else {
if len(o.Lower) == 0 {
return msg.WrapErr(EINVAL, "overlay requires at least one lowerdir")
}
options = append(options,
OptionOverlayUpperdir+"="+o.upper,
OptionOverlayWorkdir+"="+o.work)
}
options = append(options,
OptionOverlayLowerdir+"="+strings.Join(o.lower, SpecialOverlayPath),
OptionOverlayUserxattr)
return wrapErrSuffix(Mount(SourceOverlay, target, FstypeOverlay, 0, strings.Join(options, SpecialOverlayOption)),
fmt.Sprintf("cannot mount overlay on %q:", o.Target))
}
func (o *MountOverlayOp) Is(op Op) bool {
vo, ok := op.(*MountOverlayOp)
return ok && ((o == nil && vo == nil) || (o != nil && vo != nil &&
o.Target != nil && vo.Target != nil && o.Target.Is(vo.Target) &&
slices.EqualFunc(o.Lower, vo.Lower, func(a *Absolute, v *Absolute) bool { return a.Is(v) }) &&
o.Upper.Is(vo.Upper) && o.Work.Is(vo.Work)))
}
func (*MountOverlayOp) prefix() string { return "mounting" }
func (o *MountOverlayOp) String() string {
return fmt.Sprintf("overlay on %q with %d layers", o.Target, len(o.Lower))
}
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