Remove View.First() and View.RemoveFirst()

These methods let users eaily break the VectorisedView abstraction, and
allowed netstack to slip into pseudo-enforcement of the "all headers are
in the first View" invariant. Removing them and replacing with PullUp(n)
breaks this reliance and will make it easier to add iptables support and
rework network buffer management.

The new View.PullUp(n) method is low cost in the common case, when when
all the headers fit in the first View.

PiperOrigin-RevId: 308163542

3 files changed, 59 insertions, 2 deletions

diff --git a/pkg/tcpip/link/rawfile/BUILD b/pkg/tcpip/link/rawfile/BUILD
index 14b527bc2..9cc08d0e2 100644
--- a/pkg/tcpip/link/rawfile/BUILD
+++ b/pkg/tcpip/link/rawfile/BUILD
@@ -1,4 +1,4 @@
-load("//tools:defs.bzl", "go_library")
+load("//tools:defs.bzl", "go_library", "go_test")
 
 package(licenses = ["notice"])
 
@@ -18,3 +18,10 @@ go_library(
         "@org_golang_x_sys//unix:go_default_library",
     ],
 )
+
+go_test(
+    name = "rawfile_test",
+    size = "small",
+    srcs = ["rawfile_test.go"],
+    library = ":rawfile",
+)
diff --git a/pkg/tcpip/link/rawfile/rawfile_test.go b/pkg/tcpip/link/rawfile/rawfile_test.go
new file mode 100644
index 000000000..8f14ba761
--- /dev/null
+++ b/pkg/tcpip/link/rawfile/rawfile_test.go
@@ -0,0 +1,46 @@
+// 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.
+
+// +build linux
+
+package rawfile
+
+import (
+	"syscall"
+	"testing"
+)
+
+func TestNonBlockingWrite3ZeroLength(t *testing.T) {
+	fd, err := syscall.Open("/dev/null", syscall.O_WRONLY, 0)
+	if err != nil {
+		t.Fatalf("failed to open /dev/null: %v", err)
+	}
+	defer syscall.Close(fd)
+
+	if err := NonBlockingWrite3(fd, []byte{}, []byte{0}, nil); err != nil {
+		t.Fatalf("failed to write: %v", err)
+	}
+}
+
+func TestNonBlockingWrite3Nil(t *testing.T) {
+	fd, err := syscall.Open("/dev/null", syscall.O_WRONLY, 0)
+	if err != nil {
+		t.Fatalf("failed to open /dev/null: %v", err)
+	}
+	defer syscall.Close(fd)
+
+	if err := NonBlockingWrite3(fd, nil, []byte{0}, nil); err != nil {
+		t.Fatalf("failed to write: %v", err)
+	}
+}
diff --git a/pkg/tcpip/link/rawfile/rawfile_unsafe.go b/pkg/tcpip/link/rawfile/rawfile_unsafe.go
index 44e25d475..92efd0bf8 100644
--- a/pkg/tcpip/link/rawfile/rawfile_unsafe.go
+++ b/pkg/tcpip/link/rawfile/rawfile_unsafe.go
@@ -76,9 +76,13 @@ func NonBlockingWrite3(fd int, b1, b2, b3 []byte) *tcpip.Error {
 
 	// We have two buffers. Build the iovec that represents them and issue
 	// a writev syscall.
+	var base *byte
+	if len(b1) > 0 {
+		base = &b1[0]
+	}
 	iovec := [3]syscall.Iovec{
 		{
-			Base: &b1[0],
+			Base: base,
 			Len:  uint64(len(b1)),
 		},
 		{