X turn example/hello to return real non-small content

I need this to compare speed wrt github.com/jacobsa/fuse which does not
have ready loopback demo.

Out of the box github.com/jacobsa/fuse turned out to be ~ 1.6x slower
than github.com/hanwen/go-fuse.

with github.com/hanwen/go-fuse:

        .../github.com/hanwen/go-fuse/example/benchmark-read-throughput$ md5sum ~/mnt/tmp/file.txt
        f4cbd65f70761c9c5306d9301422af02  /home/kirr/mnt/tmp/file.txt

        .../github.com/hanwen/go-fuse/example/benchmark-read-throughput$ go run readbench.go -bs 128 -limit 30000 ~/mnt/tmp/file.txt
        block size 128 kb: 30000.4 MB in 9.704823906s: 3091.29 MBs/s

with github.com/jacobsa/fuse

        .../github.com/hanwen/go-fuse/example/benchmark-read-throughput$ md5sum ~/mnt/tmp/hello
        f4cbd65f70761c9c5306d9301422af02  /home/kirr/mnt/tmp/hello

        .../github.com/hanwen/go-fuse/example/benchmark-read-throughput$ go run readbench.go -bs 128 -limit 30000 ~/mnt/tmp/hello
        block size 128 kb: 30000.4 MB in 15.701199318s: 1910.71 MBs/s

See also https://github.com/hanwen/go-fuse/issues/192#issuecomment-338198877

example/hello/main.go

@@ -9,6 +9,7 @@ package main
 import (
 	"flag"
 	"log"
+	"io/ioutil"
 
 	"github.com/hanwen/go-fuse/fuse"
 	"github.com/hanwen/go-fuse/fuse/nodefs"
@@ -41,6 +42,17 @@ func (me *HelloFs) OpenDir(name string, context *fuse.Context) (c []fuse.DirEntr
 	return nil, fuse.ENOENT
 }
 
+
+var data []byte
+func init() {
+	var err error
+        data, err = ioutil.ReadFile("/boot/initrd.img-4.16.0-2-amd64")
+        if err != nil {
+                panic(err)
+        }
+}
+
+
 func (me *HelloFs) Open(name string, flags uint32, context *fuse.Context) (file nodefs.File, code fuse.Status) {
 	if name != "file.txt" {
 		return nil, fuse.ENOENT
@@ -48,7 +60,9 @@ func (me *HelloFs) Open(name string, flags uint32, context *fuse.Context) (file
 	if flags&fuse.O_ANYWRITE != 0 {
 		return nil, fuse.EPERM
 	}
-	return nodefs.NewDataFile([]byte(name)), fuse.OK
+
+	return nodefs.NewDataFile(data), fuse.OK
+	//return nodefs.NewDataFile([]byte(name)), fuse.OK
 }
 
 func main() {

[Kirill Smelkov]

As of 20200311 go-fuse v2 (v2.0.2-55-gfe141f3) provides even better speed:

hellofs using fuse/nodefs API (i.e. old v1/nodefs style):

.../github.com/hanwen/go-fuse/example/benchmark-read-throughput$ go run readbench.go -bs 128 -limit 30000 ~/mnt/tmp/file.txt
block size 128 kb: 30006.7 MB in 10.605658901s: 2829.31 MBs/s

hellofs using fs API (i.e. v2 style (*)):

(neo) (z-dev) (g.env) kirr@deco:~/src/neo/src/github.com/hanwen/go-fuse/example/benchmark-read-throughput$ go run readbench.go -bs 128 -limit 30000 ~/mnt/tmp/file.txt
block size 128 kb: 30006.7 MB in 5.199423433s: 5771.15 MBs/s

jacobsa/fuse stays at approx old ~1.8GB/s for both its master (2f654264), and if patched to call handleOp directly instead of in goroutine: jacobsa-fuse@59a13571, jacobsa-fuse@e891cd16.

(*) patch to benchmark for recent hellofs:

--- a/example/hello/main.go
+++ b/example/hello/main.go
@@ -11,6 +11,7 @@ import (
        "flag"
        "log"
        "syscall"
+       "io/ioutil"
 
        "github.com/hanwen/go-fuse/v2/fs"
        "github.com/hanwen/go-fuse/v2/fuse"
@@ -23,7 +24,8 @@ type HelloRoot struct {
 func (r *HelloRoot) OnAdd(ctx context.Context) {
        ch := r.NewPersistentInode(
                ctx, &fs.MemRegularFile{
-                       Data: []byte("file.txt"),
+                       //Data: []byte("file.txt"),
+                       Data: data,
                        Attr: fuse.Attr{
                                Mode: 0644,
                        },
@@ -39,6 +41,16 @@ func (r *HelloRoot) Getattr(ctx context.Context, fh fs.FileHandle, out *fuse.Att
 var _ = (fs.NodeGetattrer)((*HelloRoot)(nil))
 var _ = (fs.NodeOnAdder)((*HelloRoot)(nil))
 
+var data []byte
+func init() {
+       var err error
+        data, err = ioutil.ReadFile("/boot/initrd.img-4.19.0-8-amd64")
+        if err != nil {
+                panic(err)
+        }
+}
+
+
 func main() {
        debug := flag.Bool("debug", false, "print debug data")
        flag.Parse()

[Kirill Smelkov]

hellofs using fs API (i.e. v2 style (*)):

(neo) (z-dev) (g.env) kirr@deco:~/src/neo/src/github.com/hanwen/go-fuse/example/benchmark-read-throughput$ > go run readbench.go -bs 128 -limit 30000 ~/mnt/tmp/file.txt
block size 128 kb: 30006.7 MB in 5.199423433s: 5771.15 MBs/s

This turned to be false alarm because v2 mem-based fs is using FOPEN_KEEP_CACHE: https://github.com/jacobsa/fuse/issues/78#issuecomment-598194070.