VFS Layer

• Virtual Filesystem layer provides a common interface for filesystem operations
• Abstracts details with common methods
• Many different implementations of VFS layers in OS’

Filesystem in Userspace (FUSE)

• Allows filesys operations to call back into userspace for implementations
• A common methods for implementing filesystems

Network Filesystem (NFS) Client

• Sends VOP (Virtual Operations) requests to the server
• Request are services across the network
• Client interacts with NFS server to perform file operations

Client/Server Communication:

• Commands are fulfilled remotely through remote procedure called (RPCs)
• RPC frameworks like Java RMI, gRPC, JSON-RPC, CORBA, and SOAP are used for communication
• Communication involves sending requests from the client to the server for processing

SunRPC

• Protocol for data marshalling, unmarshalling defined in RFC 1831
• Stub functions on the local side convert arguments to network RPC…
• …while server functions on the remote side converts RPC to actual operations
• Both functions generated via rpcgen(1) from Interface Definition Language (IDL)

NFS RPC Flow

• Connect to SunRPC portmapper (port 111)
• Ask for mountd protocol port
• Connect to mountd service
• Request access to a named filesystem via NFS RPC

NFS and Security

• NVSv3: Lacks authentication and crypto after mounting
  • granting further access by holding file handles
• NFSv4: Designed with universal encryption
  • System security concerns: superuser can claim any user ID, requiring additional measures like IPSec