Implement setattr+clunk in 9P

This is to cover the common pattern: open->read/write->close,
where SetAttr needs to be called to update atime/mtime before
the file is closed.

Benchmark results:

BM_OpenReadClose/10240 CPU
setattr+clunk: 63783 ns
VFS2:          68109 ns
VFS1:          72507 ns

Updates #1198

PiperOrigin-RevId: 329628461

2 files changed, 77 insertions, 0 deletions

diff --git a/test/perf/linux/BUILD b/test/perf/linux/BUILD
index b4e907826..dd1d2438c 100644
--- a/test/perf/linux/BUILD
+++ b/test/perf/linux/BUILD
@@ -354,3 +354,19 @@ cc_binary(
         "//test/util:test_util",
     ],
 )
+
+cc_binary(
+    name = "open_read_close_benchmark",
+    testonly = 1,
+    srcs = [
+        "open_read_close_benchmark.cc",
+    ],
+    deps = [
+        gbenchmark,
+        gtest,
+        "//test/util:fs_util",
+        "//test/util:logging",
+        "//test/util:temp_path",
+        "//test/util:test_main",
+    ],
+)
diff --git a/test/perf/linux/open_read_close_benchmark.cc b/test/perf/linux/open_read_close_benchmark.cc
new file mode 100644
index 000000000..8b023a3d8
--- /dev/null
+++ b/test/perf/linux/open_read_close_benchmark.cc
@@ -0,0 +1,61 @@
+// 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.
+
+#include <fcntl.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+#include <memory>
+#include <string>
+#include <vector>
+
+#include "gtest/gtest.h"
+#include "benchmark/benchmark.h"
+#include "test/util/fs_util.h"
+#include "test/util/logging.h"
+#include "test/util/temp_path.h"
+
+namespace gvisor {
+namespace testing {
+
+namespace {
+
+void BM_OpenReadClose(benchmark::State& state) {
+  const int size = state.range(0);
+  std::vector<TempPath> cache;
+  for (int i = 0; i < size; i++) {
+    auto path = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateFileWith(
+        GetAbsoluteTestTmpdir(), "some content", 0644));
+    cache.emplace_back(std::move(path));
+  }
+
+  char buf[1];
+  unsigned int seed = 1;
+  for (auto _ : state) {
+    const int chosen = rand_r(&seed) % size;
+    int fd = open(cache[chosen].path().c_str(), O_RDONLY);
+    TEST_CHECK(fd != -1);
+    TEST_CHECK(read(fd, buf, 1) == 1);
+    close(fd);
+  }
+}
+
+// Gofer dentry cache is 1000 by default. Go over it to force files to be closed
+// for real.
+BENCHMARK(BM_OpenReadClose)->Range(1000, 16384)->UseRealTime();
+
+}  // namespace
+
+}  // namespace testing
+}  // namespace gvisor