Add vfs.Pathname{WithDeleted,ForGetcwd}.

The former is needed for vfs.FileDescription to implement
memmap.MappingIdentity, and the latter is needed to implement getcwd(2).

PiperOrigin-RevId: 285051855

1 files changed, 26 insertions, 0 deletions

diff --git a/pkg/sentry/vfs/filesystem_impl_util.go b/pkg/sentry/vfs/filesystem_impl_util.go
index 465e610e0..7315a588e 100644
--- a/pkg/sentry/vfs/filesystem_impl_util.go
+++ b/pkg/sentry/vfs/filesystem_impl_util.go
@@ -16,6 +16,8 @@ package vfs
 
 import (
 	"strings"
+
+	"gvisor.dev/gvisor/pkg/fspath"
 )
 
 // GenericParseMountOptions parses a comma-separated list of options of the
@@ -41,3 +43,27 @@ func GenericParseMountOptions(str string) map[string]string {
 	}
 	return m
 }
+
+// GenericPrependPath may be used by implementations of
+// FilesystemImpl.PrependPath() for which a single statically-determined lock
+// or set of locks is sufficient to ensure its preconditions (as opposed to
+// e.g. per-Dentry locks).
+//
+// Preconditions: Dentry.Name() and Dentry.Parent() must be held constant for
+// vd.Dentry() and all of its ancestors.
+func GenericPrependPath(vfsroot, vd VirtualDentry, b *fspath.Builder) error {
+	mnt, d := vd.mount, vd.dentry
+	for {
+		if mnt == vfsroot.mount && d == vfsroot.dentry {
+			return PrependPathAtVFSRootError{}
+		}
+		if d == mnt.root {
+			return nil
+		}
+		if d.parent == nil {
+			return PrependPathAtNonMountRootError{}
+		}
+		b.PrependComponent(d.name)
+		d = d.parent
+	}
+}