Port most syscalls to VFS2.

pipe and pipe2 aren't ported, pending a slight rework of pipe FDs for VFS2.
mount and umount2 aren't ported out of temporary laziness. access and faccessat
need additional FSImpl methods to implement properly, but are stubbed to
prevent googletest from CHECK-failing. Other syscalls require additional
plumbing.

Updates #1623

PiperOrigin-RevId: 297188448

4 files changed, 13 insertions, 29 deletions

diff --git a/pkg/fspath/BUILD b/pkg/fspath/BUILD
index ee84471b2..67dd1e225 100644
--- a/pkg/fspath/BUILD
+++ b/pkg/fspath/BUILD
@@ -8,9 +8,11 @@ go_library(
     name = "fspath",
     srcs = [
         "builder.go",
-        "builder_unsafe.go",
         "fspath.go",
     ],
+    deps = [
+        "//pkg/gohacks",
+    ],
 )
 
 go_test(
diff --git a/pkg/fspath/builder.go b/pkg/fspath/builder.go
index 7ddb36826..6318d3874 100644
--- a/pkg/fspath/builder.go
+++ b/pkg/fspath/builder.go
@@ -16,6 +16,8 @@ package fspath
 
 import (
 	"fmt"
+
+	"gvisor.dev/gvisor/pkg/gohacks"
 )
 
 // Builder is similar to strings.Builder, but is used to produce pathnames
@@ -102,3 +104,9 @@ func (b *Builder) AppendString(str string) {
 	copy(b.buf[b.start:], b.buf[oldStart:])
 	copy(b.buf[len(b.buf)-len(str):], str)
 }
+
+// String returns the accumulated string. No other methods should be called
+// after String.
+func (b *Builder) String() string {
+	return gohacks.StringFromImmutableBytes(b.buf[b.start:])
+}
diff --git a/pkg/fspath/builder_unsafe.go b/pkg/fspath/builder_unsafe.go
deleted file mode 100644
index 75606808d..000000000
--- a/pkg/fspath/builder_unsafe.go
+++ /dev/null
@@ -1,27 +0,0 @@
-// 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 fspath
-
-import (
-	"unsafe"
-)
-
-// String returns the accumulated string. No other methods should be called
-// after String.
-func (b *Builder) String() string {
-	bs := b.buf[b.start:]
-	// Compare strings.Builder.String().
-	return *(*string)(unsafe.Pointer(&bs))
-}
diff --git a/pkg/fspath/fspath.go b/pkg/fspath/fspath.go
index 9fb3fee24..4c983d5fd 100644
--- a/pkg/fspath/fspath.go
+++ b/pkg/fspath/fspath.go
@@ -67,7 +67,8 @@ func Parse(pathname string) Path {
 
 // Path contains the information contained in a pathname string.
 //
-// Path is copyable by value.
+// Path is copyable by value. The zero value for Path is equivalent to
+// fspath.Parse(""), i.e. the empty path.
 type Path struct {
 	// Begin is an iterator to the first path component in the relative part of
 	// the path.