For example, if the key is a string (or not from an integer series), then a hash map can be used for faster lookup however, if the key is like an index, then an array map will provide the fastest lookup method.Ī key cannot be bigger than key_size, it cannot store a value bigger than value_size, and max_entries is the maximum number of key-value pairs that can be stored within a map. There are different types of maps (e.g., hash, array, program array, etc.), that are chosen based on the use or need.
Maximum number of elements (max_entries).We will need some type of memory/data structure within the kernel to create such stats. Maps are a generic data structure that store different types of data in the form of key-value pairs. They allow sharing of data between eBPF kernel programs, and between kernel and user-space applications. attr can be a user-defined structure that can be used by its respective command.ĮBPF tracing calculates the stats in the kernel domain itself.cmd can be any defined enum bpf_cmd, which tell the kernel about management of the map area (e.g., creating, updating, deleting, finding an element, attaching or detaching a program, etc.).BPF system callĪ user can interact with the eBPF kernel using a bpf() system call whose prototype is: int bpf (int cmd, union bpf_attr *attr, unsigned int size ) įollowing is a summary of those arguments see man page BPF for more details. eBPF tracing: User space to kernel space flowīPF system call and BPF maps are two useful entities that can interact with the eBPF kernel. Perf has also a BPF interface that can be used to load eBPF objects into kernel. Take a look at these files and directories for more on the upstream kernel for eBPF use:īCC is another out-of-kernel tree tool that has efficient kernel tracing programs for specific usage (such as funccount, which counts functions matching a pattern). Userspace tools have been developed for both the in-kernel tree and the out-of-kernel tree. They have been supported with Arch x86-64, AArch64, S390x, PowerPC 64, and SPARC64.įor more information, look at these Linux kernel files: So far, support of kprobes, tracepoints, and perf_events filtering using eBPF have been implemented in the upstream kernel. Traditional built-in tracers in Linux are used in a post-process manner, where they dump fixed-event details, then userspace tools like perf or trace-cmd can post processes to get required information (e.g., perf stat) however, eBPF can prepare user information in kernel context and transfer only needed information to user space.
eBPF and tracing review Upstream kernel development
#Istat menus daemon berkeley packet filter code#
eBPF has been designed to be JIT'ed with one-to-one mapping, so it can generate very optimized code that performs as fast as natively compiled code. Further, an eBPF program can be written in C-like functions, which can be compiled using a GNU Compiler Collection (GCC)/LLVM compiler. Therefore eBPF can also be used for aggregating statistics of events. It also includes a global data store called maps, and this maps state persists between events. Whereas BPF has forward jumps, eBPF has both backwards and forwards jumps, so there can be a loop, which, of course, the kernel ensures terminates properly. eBPF machineĮxtended BPF (eBPF) is an enhancement over BPF (which is now called cBPF, which stands for classical BPF) with more resources, such as 10 registers and 1-8 byte load/store instructions. Such a compiler exists for x86-64, SPARC, PowerPC, ARM, ARM64, MIPS, and System 390 and can be enabled through CONFIG_BPF_JIT.
This compiler translates BPF bytecode into a host system's assembly code. BPF just-in-time compilerĪ just-in-time (JIT) compiler was introduced into the kernel in 2011 to speed up BPF bytecode execution. If it is not an IP packet, 0 will be returned, and the packet will be rejected. The ldh instruction loads a half-word (16-bit) value in the accumulator from offset 12 in the Ethernet packet, which is an Ethernet-type field.
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