convert virtiofs driver to support the new virtqueue implementation

[stlankes]

This PR converts the old virtio-fs driver and tested it with virtiofsd. The old version are written for the old virtio implementation. To test the interface, a local directory is mapped within the guest to /root. The demo application is able to create a file foo.txt and is also able to read the file (see create_file in examples/demo/src/tests/mod.rs ).

Build demo:

$ cargo build -Zbuild-std=std,panic_abort --target x86_64-unknown-hermit -p rusty_demo --release

Run following demo as root:

$ mkdir testdir
$ virtiofsd --socket-path=./vhostqemu --shared-dir ./testdir --announce-submounts --sandbox none --seccomp none --inode-file-handles=never
$ qemu-system-x86_64 -display none -smp 1 -m 1G -serial stdio \
            -cpu qemu64,apic,fsgsbase,rdtscp,xsave,xsaveopt,fxsr \
            -device isa-debug-exit,iobase=0xf4,iosize=0x04 \
            -kernel rusty-loader-x86_64 \
            -chardev socket,id=char0,path=./vhostqemu \
            -device vhost-user-fs-pci,queue-size=1024,chardev=char0,tag=root \
            -object memory-backend-file,id=mem,size=1G,mem-path=/dev/shm,share=on -numa node,memdev=mem \
            -initrd target/x86_64-unknown-hermit/release/rusty_demo

[mkroening]

Looks good to me!

bors r+

[bors]

Build succeeded:

• Build
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• ci/gitlab/git.rwth-aachen.de
• Clippy
• Format
• Run RustyHermit (aarch64)
• Run RustyHermit (x86_64)
• Test