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

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

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

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

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

6. 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

7. 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

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

9. 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

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

11. 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

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

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

14. 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

15. 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

16. Poll/Select/Kqueue
Implements Timeout
BPF meets UVM

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

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