BPF meets UVM Michael Stolarchuk LISA 2001 Dec 6, 2001 BPF meets UVM

Executive Summary BPF can be improved UVM can help BPF meets UVM

Current BPF Model BPF BPF buffers User Process MBUF Device Drivers BPF meets UVM

BPF Copies copies BPF BPF buffers User Process MBUF Device Drivers BPF meets UVM

BPF Copies Mbufs into BPF buffer User process copies by issuing read BPF meets UVM

1 Copy Model Mbuf to BPF buffer copy BPF buffer mapped into user address space Mapped region READ-ONLY Allow REASONABLE sized buffers BPF meets UVM

1 Copy Breaks Semantics Packet Data Region Can’t be written Checksum generation Encryption Read no longer returns packets Returns state of active buffers BPF meets UVM

Multiple Buffers New BPF allows multiple buffers Of process configured sizes BPF meets UVM

State Changes Each buffer has an associated state Null, Empty, Data, Data-Time-Out, Hold Read returns when state transitions occur Not all transitions awaken read Ioctl’s control some of the read-wakeups Ioctl’s manage user process release of buffers BPF meets UVM

Example Bpf filling hold data mt hold 1 2 3 4 User process owns BPF meets UVM

More work to set up Describes number of buffers, size of buffers Requests memory mapping Allows bpf to be backwards compatable Requests features supported Sets features desired BPF meets UVM

But WAIT… Improve semantics time-out FIONREAD packet loss Select/Poll/Kqueue BPF meets UVM

Time Out Starts when data appears in a Buffer Provides Non-blocking to co-exist with timeout Simple threading implementations work BPF meets UVM

FIONREAD Returns when data is available to read Allows user process to check for data Old version returns chars in buffer, but NOT whether a read would block BPF meets UVM

Packet Loss Inline description of packet loss No longer need to `poll’ to see if data is lost Locates missing data in the data stream Allows damaged sessions to be marked BPF meets UVM

Poll/Select/Kqueue Implements Timeout BPF meets UVM

Bpf “Messages” Compatable format improvement Allows abstract information to be encoded Device checksums Packet loss Capture counts Filter counts BPF meets UVM

Next Improvements Process `owned’ buffers 0-Copy BPF BPF meets UVM