Stub out readahead implementation.

Closes #261

PiperOrigin-RevId: 270973347

pkg/sentry/syscalls/linux/linux64.go

@@ -232,7 +232,7 @@ var AMD64 = &kernel.SyscallTable{
 		184: syscalls.Error("tuxcall", syserror.ENOSYS, "Not implemented in Linux.", nil),
 		185: syscalls.Error("security", syserror.ENOSYS, "Not implemented in Linux.", nil),
 		186: syscalls.Supported("gettid", Gettid),
-		187: syscalls.ErrorWithEvent("readahead", syserror.ENOSYS, "", []string{"gvisor.dev/issue/261"}), // TODO(b/29351341)
+		187: syscalls.Supported("readahead", Readahead),
 		188: syscalls.Error("setxattr", syserror.ENOTSUP, "Requires filesystem support.", nil),
 		189: syscalls.Error("lsetxattr", syserror.ENOTSUP, "Requires filesystem support.", nil),
 		190: syscalls.Error("fsetxattr", syserror.ENOTSUP, "Requires filesystem support.", nil),

pkg/sentry/syscalls/linux/sys_read.go

@@ -72,6 +72,39 @@ func Read(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallC
 	return uintptr(n), nil, handleIOError(t, n != 0, err, kernel.ERESTARTSYS, "read", file)
 }
 
+// Readahead implements readahead(2).
+func Readahead(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
+	fd := args[0].Int()
+	offset := args[1].Int64()
+	size := args[2].SizeT()
+
+	file := t.GetFile(fd)
+	if file == nil {
+		return 0, nil, syserror.EBADF
+	}
+	defer file.DecRef()
+
+	// Check that the file is readable.
+	if !file.Flags().Read {
+		return 0, nil, syserror.EBADF
+	}
+
+	// Check that the size is valid.
+	if int(size) < 0 {
+		return 0, nil, syserror.EINVAL
+	}
+
+	// Check that the offset is legitimate.
+	if offset < 0 {
+		return 0, nil, syserror.EINVAL
+	}
+
+	// Return EINVAL; if the underlying file type does not support readahead,
+	// then Linux will return EINVAL to indicate as much. In the future, we
+	// may extend this function to actually support readahead hints.
+	return 0, nil, syserror.EINVAL
+}
+
 // Pread64 implements linux syscall pread64(2).
 func Pread64(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
 	fd := args[0].Int()

test/syscalls/BUILD

@@ -345,6 +345,11 @@ syscall_test(
     test = "//test/syscalls/linux:read_test",
 )
 
+syscall_test(
+    add_overlay = True,
+    test = "//test/syscalls/linux:readahead_test",
+)
+
 syscall_test(
     size = "medium",
     shard_count = 5,

test/syscalls/linux/BUILD

@@ -1735,6 +1735,20 @@ cc_binary(
     ],
 )
 
+cc_binary(
+    name = "readahead_test",
+    testonly = 1,
+    srcs = ["readahead.cc"],
+    linkstatic = 1,
+    deps = [
+        "//test/util:file_descriptor",
+        "//test/util:temp_path",
+        "//test/util:test_main",
+        "//test/util:test_util",
+        "@com_google_googletest//:gtest",
+    ],
+)
+
 cc_binary(
     name = "readv_test",
     testonly = 1,

test/syscalls/linux/readahead.cc

@@ -0,0 +1,91 @@
+// 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.
+
+#include <errno.h>
+#include <fcntl.h>
+
+#include "gtest/gtest.h"
+#include "test/util/file_descriptor.h"
+#include "test/util/temp_path.h"
+#include "test/util/test_util.h"
+
+namespace gvisor {
+namespace testing {
+
+namespace {
+
+TEST(ReadaheadTest, InvalidFD) {
+  EXPECT_THAT(readahead(-1, 1, 1), SyscallFailsWithErrno(EBADF));
+}
+
+TEST(ReadaheadTest, InvalidOffset) {
+  const TempPath in_file = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateFile());
+  const FileDescriptor fd =
+      ASSERT_NO_ERRNO_AND_VALUE(Open(in_file.path(), O_RDWR));
+  EXPECT_THAT(readahead(fd.get(), -1, 1), SyscallFailsWithErrno(EINVAL));
+}
+
+TEST(ReadaheadTest, ValidOffset) {
+  constexpr char kData[] = "123";
+  const TempPath in_file = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateFileWith(
+      GetAbsoluteTestTmpdir(), kData, TempPath::kDefaultFileMode));
+  const FileDescriptor fd =
+      ASSERT_NO_ERRNO_AND_VALUE(Open(in_file.path(), O_RDWR));
+
+  // N.B. The implementation of readahead is filesystem-specific, and a file
+  // backed by ram may return EINVAL because there is nothing to be read.
+  EXPECT_THAT(readahead(fd.get(), 1, 1), AnyOf(SyscallSucceedsWithValue(0),
+                                               SyscallFailsWithErrno(EINVAL)));
+}
+
+TEST(ReadaheadTest, PastEnd) {
+  constexpr char kData[] = "123";
+  const TempPath in_file = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateFileWith(
+      GetAbsoluteTestTmpdir(), kData, TempPath::kDefaultFileMode));
+  const FileDescriptor fd =
+      ASSERT_NO_ERRNO_AND_VALUE(Open(in_file.path(), O_RDWR));
+  // See above.
+  EXPECT_THAT(readahead(fd.get(), 2, 2), AnyOf(SyscallSucceedsWithValue(0),
+                                               SyscallFailsWithErrno(EINVAL)));
+}
+
+TEST(ReadaheadTest, CrossesEnd) {
+  constexpr char kData[] = "123";
+  const TempPath in_file = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateFileWith(
+      GetAbsoluteTestTmpdir(), kData, TempPath::kDefaultFileMode));
+  const FileDescriptor fd =
+      ASSERT_NO_ERRNO_AND_VALUE(Open(in_file.path(), O_RDWR));
+  // See above.
+  EXPECT_THAT(readahead(fd.get(), 4, 2), AnyOf(SyscallSucceedsWithValue(0),
+                                               SyscallFailsWithErrno(EINVAL)));
+}
+
+TEST(ReadaheadTest, WriteOnly) {
+  const TempPath in_file = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateFile());
+  const FileDescriptor fd =
+      ASSERT_NO_ERRNO_AND_VALUE(Open(in_file.path(), O_WRONLY));
+  EXPECT_THAT(readahead(fd.get(), 0, 1), SyscallFailsWithErrno(EBADF));
+}
+
+TEST(ReadaheadTest, InvalidSize) {
+  const TempPath in_file = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateFile());
+  const FileDescriptor fd =
+      ASSERT_NO_ERRNO_AND_VALUE(Open(in_file.path(), O_RDWR));
+  EXPECT_THAT(readahead(fd.get(), 0, -1), SyscallFailsWithErrno(EINVAL));
+}
+
+}  // namespace
+
+}  // namespace testing
+}  // namespace gvisor