2019-12-11 21:40:57 +00:00
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// Copyright 2019 The gVisor Authors.
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//
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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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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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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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package vfs
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import (
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"gvisor.dev/gvisor/pkg/fspath"
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"gvisor.dev/gvisor/pkg/sentry/context"
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2020-01-10 06:00:42 +00:00
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"gvisor.dev/gvisor/pkg/sync"
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2019-12-11 21:40:57 +00:00
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"gvisor.dev/gvisor/pkg/syserror"
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)
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var fspathBuilderPool = sync.Pool{
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New: func() interface{} {
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return &fspath.Builder{}
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},
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}
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func getFSPathBuilder() *fspath.Builder {
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return fspathBuilderPool.Get().(*fspath.Builder)
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}
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func putFSPathBuilder(b *fspath.Builder) {
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// No methods can be called on b after b.String(), so reset it to its zero
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// value (as returned by fspathBuilderPool.New) instead.
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*b = fspath.Builder{}
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fspathBuilderPool.Put(b)
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}
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// PathnameWithDeleted returns an absolute pathname to vd, consistent with
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// Linux's d_path(). In particular, if vd.Dentry() has been disowned,
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// PathnameWithDeleted appends " (deleted)" to the returned pathname.
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func (vfs *VirtualFilesystem) PathnameWithDeleted(ctx context.Context, vfsroot, vd VirtualDentry) (string, error) {
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b := getFSPathBuilder()
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defer putFSPathBuilder(b)
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haveRef := false
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defer func() {
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if haveRef {
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vd.DecRef()
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}
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}()
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origD := vd.dentry
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loop:
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for {
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err := vd.mount.fs.impl.PrependPath(ctx, vfsroot, vd, b)
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switch err.(type) {
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case nil:
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if vd.mount == vfsroot.mount && vd.mount.root == vfsroot.dentry {
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// GenericPrependPath() will have returned
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// PrependPathAtVFSRootError in this case since it checks
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// against vfsroot before mnt.root, but other implementations
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// of FilesystemImpl.PrependPath() may return nil instead.
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break loop
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}
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nextVD := vfs.getMountpointAt(vd.mount, vfsroot)
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if !nextVD.Ok() {
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break loop
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}
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if haveRef {
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vd.DecRef()
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}
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vd = nextVD
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haveRef = true
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// continue loop
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case PrependPathSyntheticError:
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// Skip prepending "/" and appending " (deleted)".
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return b.String(), nil
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case PrependPathAtVFSRootError, PrependPathAtNonMountRootError:
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break loop
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default:
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return "", err
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}
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}
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b.PrependByte('/')
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if origD.IsDisowned() {
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b.AppendString(" (deleted)")
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}
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return b.String(), nil
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}
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// PathnameForGetcwd returns an absolute pathname to vd, consistent with
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// Linux's sys_getcwd().
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func (vfs *VirtualFilesystem) PathnameForGetcwd(ctx context.Context, vfsroot, vd VirtualDentry) (string, error) {
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if vd.dentry.IsDisowned() {
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return "", syserror.ENOENT
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}
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b := getFSPathBuilder()
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defer putFSPathBuilder(b)
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haveRef := false
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defer func() {
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if haveRef {
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vd.DecRef()
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}
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}()
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unreachable := false
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loop:
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for {
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err := vd.mount.fs.impl.PrependPath(ctx, vfsroot, vd, b)
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switch err.(type) {
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case nil:
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if vd.mount == vfsroot.mount && vd.mount.root == vfsroot.dentry {
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break loop
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}
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nextVD := vfs.getMountpointAt(vd.mount, vfsroot)
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if !nextVD.Ok() {
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unreachable = true
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break loop
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}
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if haveRef {
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vd.DecRef()
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}
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vd = nextVD
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haveRef = true
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case PrependPathAtVFSRootError:
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break loop
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case PrependPathAtNonMountRootError, PrependPathSyntheticError:
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unreachable = true
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break loop
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default:
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return "", err
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}
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}
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b.PrependByte('/')
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if unreachable {
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b.PrependString("(unreachable)")
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}
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return b.String(), nil
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}
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// As of this writing, we do not have equivalents to:
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//
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// - d_absolute_path(), which returns EINVAL if (effectively) any call to
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// FilesystemImpl.PrependPath() would return PrependPathAtNonMountRootError.
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//
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// - dentry_path(), which does not walk up mounts (and only returns the path
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// relative to Filesystem root), but also appends "//deleted" for disowned
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// Dentries.
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//
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// These should be added as necessary.
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