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overlay: avoid creating unnecessary whiteouts in UnlinkAt and RmdirAt #12092

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overlay: avoid creating unnecessary whiteouts in UnlinkAt and RmdirAt #12092

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54 changes: 37 additions & 17 deletions pkg/sentry/fsimpl/overlay/filesystem.go
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Original file line number Diff line number Diff line change
Expand Up @@ -1405,7 +1405,8 @@ func (fs *filesystem) RmdirAt(ctx context.Context, rp *vfs.ResolvingPath) error
Start: parent.upperVD,
Path: fspath.Parse(name),
}
if child.upperVD.Ok() {
switch {
case child.upperVD.Ok():
cleanupRecreateWhiteouts := func() {
if !child.upperVD.Ok() {
return
Expand Down Expand Up @@ -1444,16 +1445,25 @@ func (fs *filesystem) RmdirAt(ctx context.Context, rp *vfs.ResolvingPath) error
cleanupRecreateWhiteouts()
return err
}
}
if err := CreateWhiteout(ctx, vfsObj, fs.creds, &pop); err != nil {
vfsObj.AbortDeleteDentry(&child.vfsd)
if child.upperVD.Ok() {
// Don't attempt to recover from this: the original directory is
// already gone, so any dentries representing it are invalid, and
// creating a new directory won't undo that.
panic(fmt.Sprintf("unrecoverable overlayfs inconsistency: failed to create whiteout after removing upper layer directory during RmdirAt: %v", err))
// Determine if the directory exists on any lower layers; if not, we
// can skip creating the whiteout.
newChildLayer, err := fs.lookupLayerLocked(ctx, parent, name)
if err == nil && newChildLayer == lookupLayerNone {
break
}
fallthrough

default:
if err := CreateWhiteout(ctx, vfsObj, fs.creds, &pop); err != nil {
vfsObj.AbortDeleteDentry(&child.vfsd)
if child.upperVD.Ok() {
// Don't attempt to recover from this: the original directory is
// already gone, so any dentries representing it are invalid, and
// creating a new directory won't undo that.
panic(fmt.Sprintf("unrecoverable overlayfs inconsistency: failed to create whiteout after removing upper layer directory during RmdirAt: %v", err))
}
return err
}
return err
}

toDecRef = vfsObj.CommitDeleteDentry(ctx, &child.vfsd)
Expand Down Expand Up @@ -1655,19 +1665,29 @@ func (fs *filesystem) UnlinkAt(ctx context.Context, rp *vfs.ResolvingPath) error
Start: parent.upperVD,
Path: fspath.Parse(name),
}
if childLayer == lookupLayerUpper {
switch {
case childLayer == lookupLayerUpper:
// Remove the existing file on the upper layer.
if err := vfsObj.UnlinkAt(ctx, fs.creds, &pop); err != nil {
vfsObj.AbortDeleteDentry(&child.vfsd)
return err
}
}
if err := CreateWhiteout(ctx, vfsObj, fs.creds, &pop); err != nil {
vfsObj.AbortDeleteDentry(&child.vfsd)
if childLayer == lookupLayerUpper {
panic(fmt.Sprintf("unrecoverable overlayfs inconsistency: failed to create whiteout after unlinking upper layer file during UnlinkAt: %v", err))
// Determine if the file exists on any lower layers; if not, we can
// skip creating the whiteout.
newChildLayer, err := fs.lookupLayerLocked(ctx, parent, name)
if err == nil && newChildLayer == lookupLayerNone {
break
}
fallthrough

default:
if err := CreateWhiteout(ctx, vfsObj, fs.creds, &pop); err != nil {
vfsObj.AbortDeleteDentry(&child.vfsd)
if childLayer == lookupLayerUpper {
panic(fmt.Sprintf("unrecoverable overlayfs inconsistency: failed to create whiteout after unlinking upper layer file during UnlinkAt: %v", err))
}
return err
}
return err
}

toDecRef = vfsObj.CommitDeleteDentry(ctx, &child.vfsd)
Expand Down