wasi: fixes fd_readdir bench (#1554)

Signed-off-by: Adrian Cole <adrian@tetrate.io>

imports/wasi_snapshot_preview1/wasi_bench_test.go

@@ -133,39 +133,35 @@ func Benchmark_fdReaddir(b *testing.B) {
 		fs   fs.FS
 		// dirMount ensures direct use of syscall.FS
 		dirMount string
-		// continued is true to test performance on a follow-up call. The
-		// preceding will call fd_read with 24 bytes, which is enough to read
-		// the initial entry's size, but not enough to read its name. This
-		// ensures the next fd_read is allowed to pass a cookie, because it
-		// read fd_next, while ensuring it will write all the entries.
-		continued bool
+		// twoCalls tests performance of reading a directory in two calls.
+		twoCalls bool
 	}{
 		{
 			name: "embed.FS",
 			fs:   embedFS,
 		},
 		{
-			name:      "embed.FS - continued",
-			fs:        embedFS,
-			continued: true,
+			name:     "embed.FS - two calls",
+			fs:       embedFS,
+			twoCalls: true,
 		},
 		{
 			name: "os.DirFS",
 			fs:   os.DirFS("testdata"),
 		},
 		{
-			name:      "os.DirFS - continued",
-			fs:        os.DirFS("testdata"),
-			continued: true,
+			name:     "os.DirFS - two calls",
+			fs:       os.DirFS("testdata"),
+			twoCalls: true,
 		},
 		{
 			name:     "sysfs.DirFS",
 			dirMount: "testdata",
 		},
 		{
-			name:      "sysfs.DirFS - continued",
-			dirMount:  "testdata",
-			continued: true,
+			name:     "sysfs.DirFS - two calls",
+			dirMount: "testdata",
+			twoCalls: true,
 		},
 	}
 
@@ -190,18 +186,6 @@ func Benchmark_fdReaddir(b *testing.B) {
 
 			fn := mod.ExportedFunction(wasip1.FdReaddirName)
 
-			// Open the root directory as a file-descriptor.
-			fsc := mod.(*wasm.ModuleInstance).Sys.FS()
-			fd, errno := fsc.OpenFile(fsc.RootFS(), ".", os.O_RDONLY, 0)
-			if errno != 0 {
-				b.Fatal(errno)
-			}
-			f, ok := fsc.LookupFile(fd)
-			if !ok {
-				b.Fatal("couldn't open fd ", fd)
-			}
-			defer fsc.CloseFile(fd) //nolint
-
 			b.ResetTimer()
 			b.ReportAllocs()
 			for i := 0; i < b.N; i++ {
@@ -212,26 +196,29 @@ func Benchmark_fdReaddir(b *testing.B) {
 				buf := 8           // where to start the dirents
 				bufLen := 8096     // allow up to 8KB buffer usage
 
-				// Recreate the file under the file-descriptor
-				if errno = f.File.Close(); errno != 0 {
+				// Open the root directory as a file-descriptor.
+				fsc := mod.(*wasm.ModuleInstance).Sys.FS()
+				fd, errno := fsc.OpenFile(fsc.RootFS(), ".", os.O_RDONLY, 0)
+				if errno != 0 {
 					b.Fatal(errno)
 				}
-				if f.File, errno = fsc.RootFS().OpenFile(".", os.O_RDONLY, 0); errno != 0 {
-					b.Fatal(errno)
-				}
-
-				// Make an initial call to build the state of an unread directory
-				if bc.continued {
-					results, err := fn.Call(testCtx, uint64(fd), uint64(buf), uint64(24), uint64(cookie), uint64(resultBufused))
-					if err != nil {
-						b.Fatal(err)
-					}
-					requireESuccess(b, results)
-					cookie = 1 // WASI doesn't document this, but we write the first d_next as 1
-				}
 
 				// Time the call to write the dirents
 				b.StartTimer()
+
+				if bc.twoCalls {
+					// Read the dot entries
+					bufLen := wasip1.DirentSize + 1 // size of "."
+					bufLen += wasip1.DirentSize + 2 // size of ".."
+
+					results, err := fn.Call(testCtx, uint64(fd), uint64(buf), uint64(bufLen), uint64(cookie), uint64(resultBufused))
+					if err != nil {
+						b.Fatal(err)
+					}
+					requireESuccess(b, results)
+					cookie = 2 // d_next of "..", the real file we couldn't read.
+				}
+
 				results, err := fn.Call(testCtx, uint64(fd), uint64(buf), uint64(bufLen), uint64(cookie), uint64(resultBufused))
 				if err != nil {
 					b.Fatal(err)
@@ -239,6 +226,9 @@ func Benchmark_fdReaddir(b *testing.B) {
 				b.StopTimer()
 
 				requireESuccess(b, results)
+				if errno = fsc.CloseFile(fd); errno != 0 {
+					b.Fatal(errno)
+				}
 			}
 		})
 	}
@@ -355,6 +345,7 @@ func Benchmark_pathFilestat(b *testing.B) {
 }
 
 func requireESuccess(b *testing.B, results []uint64) {
+	b.Helper()
 	if errno := wasip1.Errno(results[0]); errno != 0 {
 		b.Fatal(wasip1.ErrnoName(errno))
 	}