NETMAP USERSPACE UDP STACK 64 BIT
NETMAP USERSPACE UDP STACK 32 BIT
NETMAP USERSPACE UDP STACK FULL
NETMAP USERSPACE UDP STACK VERIFICATION

Events can be generated from kprobes/uprobes, tracepoints, dtrace probes, sockets and more. There is very little use in running on-demand eBPF programs from userspace as all on-demand user calls are already handled via the normal non-VM kernel API calls ('syscalls') where VM bytecode brings little value. How does it work?ĮBPF programs are run by the kernel when events occur, so they can be viewed as a form of function hooking or event driven programming.

Legalese aside, this userspace implementation can probably be useful for tracing performance-critical applications which need to avoid the cost of kernel-userspace context switches. Starting with kernel v3.18 (2014), the VM was also exposed to userspace via the bpf() syscall and uapi/linux/bpf.h which resulted in a freeze of its instruction set present at the time which became a public ABI, though new instructions can still be (and have been) added later.īecause the in-kernel eBPF implementation is licensed under GPLv2, it cannot be easily redistributed by non-GPL users so there is also an alternative Apache-licensed userspace eBPF VM implementation called 'uBPF'. Historically the eBPF VM was only available from within the kernel and was used to filter network packets without userspace interference, hence the now-nonsense name of 'Berkley Packet Filter'.

NETMAP USERSPACE UDP STACK VERIFICATION

These kinds of restrictions enable simple and fast correctness verification when an eBPF program is loaded in the kernel and its instructions get parsed into a directed-acyclic-graph by a verifier module. Some quick examples can be found in this excellent eBPF reference.īy design the eBPF VM and its programs are intentionally not Turing complete: no loops are allowed (there is work-in-progress to support bounded loops) so each eBPF program is guaranteed to finish and not hang, all memory access is bounded and type-checked (including registers, a MOV instruction can change the type of a register), there are no null dereferences, a program must have at most BPF_MAXINSNS instructions (default 4096), the 'main' function takes a single argument (the context) and so on.

NETMAP USERSPACE UDP STACK FULL

Reasons for running a full VM inside the kernel revolve around convenience and safety: While all operations done by eBPF programs can be handled via normal kernel modules, direct kernel programming is a really dangerous endeavour - it can cause lock-ups, memory corruption, crash processes, cause security vulnerabilities and other unwanted effects especially on production devices (eBPF is very often used to inspect systems in production), so running native-fast JiT-compiled kernel code via a safe VM becomes valuable for security monitoring and sandboxing, network filtering, program tracing, profiling, debugging and so on. Readers familiar with DTrace might find this Dtrace/BPFtrace comparison useful. It is also part of the mainline kernel, so it doesn't require any 3rd party modules like other frameworks (*cough* LTTng or SystemTap *cough*), and comes enabled by default in almost all Linux distributions. It is a full VM implementation, not to be confused with the Kernel-based VM (KVM) which is a module enabling Linux to act as hypervisor for other VMs.

NETMAP USERSPACE UDP STACK 64 BIT

Part 5 is about tracing userspace: Up until now our efforts were focused on tracing the kernel, so it's about time we also examine other user processes.ĮBPF is a register-based Virtual Machine using a custom 64 bit RISC instruction set capable of running Just-in-Time native-compiled 'BPF programs' inside the Linux kernel with access to a subset of kernel functions and memory.

Readers interested only in this part can probably skip the rest.

NETMAP USERSPACE UDP STACK 32 BIT

We'll cross-compile and run eBPF programs on 32 bit ARM with smaller embedded-focused tools.

Part 4 focuses on running eBPF programs on embedded systems which are resource constrained, where a full toolchain stack (BCC/LLVM/python/etc) is undesirable.

Part 3 is an overview of the userspace tooling meant to increase productivity, built on top of the low level VM mechanisms presented in parts 1 and 2.

Part 1 and Part 2 give a condensed in-depth introduction to eBPF for newcommers or those looking to further their knowledge by taking a deep dive into the lower part of the eBPF stack.

BPF and eBPF are used interchangeably in the series. The name/acronym deasn't mean much anymore because the project evolved way beyond its initial scope. Note: These blog posts will be focusing on eBPF so for our purpuses BPF and eBPF are the same thing and can be used interchangeably. Interested in learning more about low-level specifics of the eBPF stack? Read on as we take a deep dive, from its VM mechanisms and tools, to running traces on remote, resource-constrained embedded devices.

Netmap userspace udp stack