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