Network File System

Network File System (ou NFS), littéralement système de fichiers en réseau, est à l'origine un protocole développé par Sun Microsystems en 1984 qui permet à un ordinateur d'accéder via un réseau à des fichiers distants. Il fait partie de la couche application du modèle OSI et utilise le protocole RPC. Ce système de fichiers en réseau permet de partager des données principalement entre systèmes UNIX. Des versions existent pour Macintosh ou Microsoft Windows. NFS est compatible avec IPv6 sur la plupart des systèmes. NFS versions 1, 2 et 3 Les versions 1 et 2 sont non sécurisées, prévues pour fonctionner sur UDP. La version 3 est étendue pour prendre en charge TCP. Dans ces versions, la gestion de la sécurité reste élémentaire et souffre d'importantes lacunes. Le système est sans état (stateless) et ne permet pas la reprise sur incident. NFSv4 Inspirée d' (AFS), la version 4 du protocole marque une rupture totale avec les versions précédentes. L'ensemble du pr

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Système de fichiers

Le terme système de fichiers (abrégé « FS » pour File System, parfois filesystem en anglais) désigne de façon ambigüe :

soit l'organisation hiérarchique des fichiers au sein d'un système d'exploit

Système d'exploitation

En informatique, un système d'exploitation (souvent appelé OS — de l'anglais operating system — ou parfois SE — en français) est un ensemble de programmes qui dirige l'utilisation des ressources d'u

Clustered file system

A clustered file system is a which is shared by being simultaneously mounted on multiple servers. There are several approaches to clustering, most of which do not employ a clustered file system (o

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

Chargement

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

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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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Introduction to basic concepts of operating systems.

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