1 files changed, 153 insertions, 0 deletions
diff --git a/pkg/sentry/vfs/pathname.go b/pkg/sentry/vfs/pathname.go
new file mode 100644
index 000000000..8e155654f
--- /dev/null
+++ b/pkg/sentry/vfs/pathname.go
@@ -0,0 +1,153 @@
+// Copyright 2019 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 vfs
+
+import (
+	"sync"
+
+	"gvisor.dev/gvisor/pkg/fspath"
+	"gvisor.dev/gvisor/pkg/sentry/context"
+	"gvisor.dev/gvisor/pkg/syserror"
+)
+
+var fspathBuilderPool = sync.Pool{
+	New: func() interface{} {
+		return &fspath.Builder{}
+	},
+}
+
+func getFSPathBuilder() *fspath.Builder {
+	return fspathBuilderPool.Get().(*fspath.Builder)
+}
+
+func putFSPathBuilder(b *fspath.Builder) {
+	// No methods can be called on b after b.String(), so reset it to its zero
+	// value (as returned by fspathBuilderPool.New) instead.
+	*b = fspath.Builder{}
+	fspathBuilderPool.Put(b)
+}
+
+// PathnameWithDeleted returns an absolute pathname to vd, consistent with
+// Linux's d_path(). In particular, if vd.Dentry() has been disowned,
+// PathnameWithDeleted appends " (deleted)" to the returned pathname.
+func (vfs *VirtualFilesystem) PathnameWithDeleted(ctx context.Context, vfsroot, vd VirtualDentry) (string, error) {
+	b := getFSPathBuilder()
+	defer putFSPathBuilder(b)
+	haveRef := false
+	defer func() {
+		if haveRef {
+			vd.DecRef()
+		}
+	}()
+
+	origD := vd.dentry
+loop:
+	for {
+		err := vd.mount.fs.impl.PrependPath(ctx, vfsroot, vd, b)
+		switch err.(type) {
+		case nil:
+			if vd.mount == vfsroot.mount && vd.mount.root == vfsroot.dentry {
+				// GenericPrependPath() will have returned
+				// PrependPathAtVFSRootError in this case since it checks
+				// against vfsroot before mnt.root, but other implementations
+				// of FilesystemImpl.PrependPath() may return nil instead.
+				break loop
+			}
+			nextVD := vfs.getMountpointAt(vd.mount, vfsroot)
+			if !nextVD.Ok() {
+				break loop
+			}
+			if haveRef {
+				vd.DecRef()
+			}
+			vd = nextVD
+			haveRef = true
+			// continue loop
+		case PrependPathSyntheticError:
+			// Skip prepending "/" and appending " (deleted)".
+			return b.String(), nil
+		case PrependPathAtVFSRootError, PrependPathAtNonMountRootError:
+			break loop
+		default:
+			return "", err
+		}
+	}
+	b.PrependByte('/')
+	if origD.IsDisowned() {
+		b.AppendString(" (deleted)")
+	}
+	return b.String(), nil
+}
+
+// PathnameForGetcwd returns an absolute pathname to vd, consistent with
+// Linux's sys_getcwd().
+func (vfs *VirtualFilesystem) PathnameForGetcwd(ctx context.Context, vfsroot, vd VirtualDentry) (string, error) {
+	if vd.dentry.IsDisowned() {
+		return "", syserror.ENOENT
+	}
+
+	b := getFSPathBuilder()
+	defer putFSPathBuilder(b)
+	haveRef := false
+	defer func() {
+		if haveRef {
+			vd.DecRef()
+		}
+	}()
+	unreachable := false
+loop:
+	for {
+		err := vd.mount.fs.impl.PrependPath(ctx, vfsroot, vd, b)
+		switch err.(type) {
+		case nil:
+			if vd.mount == vfsroot.mount && vd.mount.root == vfsroot.dentry {
+				break loop
+			}
+			nextVD := vfs.getMountpointAt(vd.mount, vfsroot)
+			if !nextVD.Ok() {
+				unreachable = true
+				break loop
+			}
+			if haveRef {
+				vd.DecRef()
+			}
+			vd = nextVD
+			haveRef = true
+		case PrependPathAtVFSRootError:
+			break loop
+		case PrependPathAtNonMountRootError, PrependPathSyntheticError:
+			unreachable = true
+			break loop
+		default:
+			return "", err
+		}
+	}
+	b.PrependByte('/')
+	if unreachable {
+		b.PrependString("(unreachable)")
+	}
+	return b.String(), nil
+}
+
+// As of this writing, we do not have equivalents to:
+//
+// - d_absolute_path(), which returns EINVAL if (effectively) any call to
+// FilesystemImpl.PrependPath() would return PrependPathAtNonMountRootError.
+//
+// - dentry_path(), which does not walk up mounts (and only returns the path
+// relative to Filesystem root), but also appends "//deleted" for disowned
+// Dentries.
+//
+// These should be added as necessary.