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// Copyright 2020 The gVisor Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// Package genericfstree provides tools for implementing vfs.FilesystemImpls
// where a single statically-determined lock or set of locks is sufficient to
// ensure that a Dentry's name and parent are contextually immutable.
//
// Clients using this package must use the go_template_instance rule in
// tools/go_generics/defs.bzl to create an instantiation of this template
// package, providing types to use in place of Dentry.
package genericfstree
import (
"gvisor.dev/gvisor/pkg/fspath"
"gvisor.dev/gvisor/pkg/sentry/vfs"
)
// Dentry is a required type parameter that is a struct with the given fields.
//
// +stateify savable
type Dentry struct {
// vfsd is the embedded vfs.Dentry corresponding to this vfs.DentryImpl.
vfsd vfs.Dentry
// parent is the parent of this Dentry in the filesystem's tree. If this
// Dentry is a filesystem root, parent is nil.
parent *Dentry
// name is the name of this Dentry in its parent. If this Dentry is a
// filesystem root, name is unspecified.
name string
}
// IsAncestorDentry returns true if d is an ancestor of d2; that is, d is
// either d2's parent or an ancestor of d2's parent.
func IsAncestorDentry(d, d2 *Dentry) bool {
for d2 != nil { // Stop at root, where d2.parent == nil.
if d2.parent == d {
return true
}
if d2.parent == d2 {
return false
}
d2 = d2.parent
}
return false
}
// ParentOrSelf returns d.parent. If d.parent is nil, ParentOrSelf returns d.
func ParentOrSelf(d *Dentry) *Dentry {
if d.parent != nil {
return d.parent
}
return d
}
// PrependPath is a generic implementation of FilesystemImpl.PrependPath().
func PrependPath(vfsroot vfs.VirtualDentry, mnt *vfs.Mount, d *Dentry, b *fspath.Builder) error {
for {
if mnt == vfsroot.Mount() && &d.vfsd == vfsroot.Dentry() {
return vfs.PrependPathAtVFSRootError{}
}
if mnt != nil && &d.vfsd == mnt.Root() {
return nil
}
if d.parent == nil {
return vfs.PrependPathAtNonMountRootError{}
}
b.PrependComponent(d.name)
d = d.parent
}
}
// DebugPathname returns a pathname to d relative to its filesystem root.
// DebugPathname does not correspond to any Linux function; it's used to
// generate dentry pathnames for debugging.
func DebugPathname(d *Dentry) string {
var b fspath.Builder
_ = PrependPath(vfs.VirtualDentry{}, nil, d, &b)
return b.String()
}
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