Network File System

Network File System (NFS) is a protocol originally developed by Sun Microsystems (Sun) in 1984, allowing a user on a client computer to access files over a computer network much like local storage is accessed. NFS, like many other protocols, builds on the Open Network Computing Remote Procedure Call (ONC RPC) system. NFS is an open IETF standard defined in a Request for Comments (RFC), allowing anyone to implement the protocol. Versions and variations Sun used version 1 only for in-house experimental purposes. When the development team added substantial changes to NFS version 1 and released it outside of Sun, they decided to release the new version as v2, so that version interoperation and RPC version fallback could be tested. NFSv2 Version 2 of the protocol (defined in RFC 1094, March 1989) originally operated only over User Datagram Protocol (UDP). Its designers meant to keep the server side stateless, with locking (for

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On Verified Scala for STIX File System Embedded Code using Stainless

Jad Hamza, Viktor Kuncak

We present an approach for using formal methods in embedded systems and its evaluation on a case study. In our approach, the developers describe the system in a restricted subset of the high-level programming language Scala. We then use 1) a verification system to formally prove properties of such Scala program, and 2) a source-to-source translator to map Scala to C code. We have adapted the Stainless verification system to support constructs for describing embedded software (more machine integer types and early returns) and to support verification patterns needed for embedded systems code (array swap operation, pre-allocated and initialized memory, constant-length arrays). The implemented C code translator generates code that can be compiled with compilers such as GCC and integrated into larger C applications. We evaluate our approach on a case study of a file system of an instrument on the Solar Orbiter satellite. We have ported around a thousand lines of C code to Scala. We wrote specification and proof hints to make the code verify. Stainless verified the absence of run-time errors, as well as function preconditions, postconditions, and data structure invariants. The generated C code was integrated into the existing code base and exhibits very similar code size, memory use, and performance. In this process we identified multiple bugs in the well-tested code base, which were fixed in-orbit.

2022

The Distributed V Kernel and its Performance for Diskless Workstations

Willy Zwaenepoel

The distributed V kernel is a message-oriented kernel that provides uniform local and network interprocess communication. It is primarily being used in an environment of diskless workstations connected by a high-speed local network to a set of file servers. We describe a performance evaluation of the kernel, with particular emphasis on the cost of network file access. Our results show that over a local network: 1. Diskless workstations can access remote files with minimal performance penalty. 2. The V message facility can be used to access remote files at comparable cost to any well-tuned specialized file access protocol. We conclude that it is feasible to build a distributed system with all network communication using the V message facility even when most of the network nodes have no secondary storage.

1983

Media Flow Rate Allocation in Multipath Networks

Pascal Frossard, Dan Jurca

We address the problem of joint path selection and video source rate allocation in multipath streaming in order to optimize a media specific quality of service. An optimization problem is proposed, which aims at minimizing a video distortion metric based on sequence-dependent parameters, and transmission channel characteristics, for a given network infrastructure.An in-depth analysis of the media distortion evolution allows us to define a low complexity algorithm for an optimal rate allocation in multipath network scenarios. In particular, we show that a greedy allocation of rate along paths with increasing error probability leads to an optimal solution. We argue that a network path shall not be chosen for transmission, unless all other available paths with lower error probability have been chosen. Moreover, the chosen paths should be used at their maximum available end-to-end bandwidth. Simulation results show that the optimal rate allocation carefully trades off total encoding/transmission rate, with the end-to-end transmission error probability and the number of chosen paths. In many cases, the optimal rate allocation provides more than 20

2007

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