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Merge pull request #42 from olsajiri/tracing
Add tracing examples from @olsajiri
2 parents 50b9bc5 + d822333 commit 5310cfd

22 files changed

Lines changed: 2665 additions & 4 deletions

‎common/common.mk‎

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@@ -38,11 +38,13 @@ EXTRA_DEPS +=
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# BPF-prog kern and userspace shares struct via header file:
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KERN_USER_H ?= $(wildcard common_kern_user.h)
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CFLAGS ?= -I$(LIBBPF_DIR)/root/usr/include/ -I/usr/include/x86_64-linux-gnu
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CFLAGS ?= -I$(LIBBPF_DIR)/root/usr/include/ -g
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# Extra include for Ubuntu issue #44
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CFLAGS += -I/usr/include/x86_64-linux-gnu
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CFLAGS += -I../headers/
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LDFLAGS ?= -L$(LIBBPF_DIR)
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LIBS = -l:libbpf.a -lelf
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LIBS = -l:libbpf.a -lelf $(USER_LIBS)
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all: llvm-check $(USER_TARGETS) $(XDP_OBJ) $(COPY_LOADER) $(COPY_STATS)
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‎common/common_defines.h‎

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#ifndef __COMMON_DEFINES_H
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#define __COMMON_DEFINES_H
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#include <net/if.h>
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#include <linux/types.h>
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#include <stdbool.h>
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struct config {
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__u32 xdp_flags;
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int ifindex;

‎common/common_user_bpf_xdp.c‎

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@@ -179,8 +179,9 @@ struct bpf_object *load_bpf_and_xdp_attach(struct config *cfg)
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return bpf_obj;
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}
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#define XDP_UNKNOWN XDP_REDIRECT + 1
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#ifndef XDP_ACTION_MAX
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#define XDP_ACTION_MAX (XDP_REDIRECT + 1)
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#define XDP_ACTION_MAX (XDP_UNKNOWN + 1)
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#endif
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static const char *xdp_action_names[XDP_ACTION_MAX] = {
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[XDP_PASS] = "XDP_PASS",
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[XDP_TX] = "XDP_TX",
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[XDP_REDIRECT] = "XDP_REDIRECT",
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[XDP_UNKNOWN] = "XDP_UNKNOWN",
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};
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const char *action2str(__u32 action)

‎headers/linux/err.h‎

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/* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
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#ifndef __LINUX_ERR_H
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#define __LINUX_ERR_H
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#include <linux/types.h>
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#include <asm/errno.h>
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#define MAX_ERRNO 4095
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#define IS_ERR_VALUE(x) ((x) >= (unsigned long)-MAX_ERRNO)
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static inline void * ERR_PTR(long error_)
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{
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return (void *) error_;
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}
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static inline long PTR_ERR(const void *ptr)
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{
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return (long) ptr;
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}
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static inline bool IS_ERR(const void *ptr)
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{
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return IS_ERR_VALUE((unsigned long)ptr);
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}
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static inline bool IS_ERR_OR_NULL(const void *ptr)
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{
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return (!ptr) || IS_ERR_VALUE((unsigned long)ptr);
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}
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#endif

‎libbpf‎

‎tracing01-xdp-simple/Makefile‎

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# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
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# Departing from the implicit _user.c scheme
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XDP_TARGETS := trace_prog_kern xdp_prog_kern
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USER_TARGETS := trace_load_and_stats
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LIBBPF_DIR = ../libbpf/src/
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COMMON_DIR = ../common/
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include $(COMMON_DIR)/common.mk
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‎tracing01-xdp-simple/README.org‎

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# -*- fill-column: 76; -*-
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#+TITLE: Tutorial: Tracing01 - monitor xdp tracepoint
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#+OPTIONS: ^:nil
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In this lesson we will show how to create and load eBPF program that
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hooks on xdp:exception tracepoint and get its values to user space
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stats application.
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* Table of Contents :TOC:
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- [[#using-libbpf][XDP tracepoints]]
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- [[#xdp-tracepoints][XDP tracepoints]]
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- [[#tracepoint-program-section][Tracepoint program section]]
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- [[#tracepoint-arguments][Tracepoint arguments]]
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- [[#tracepoint-attaching][Tracepoint attaching]]
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- [[#hash-map][HASH map]]
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- [[#assignments][Assignments]]
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- [[#assignment-1][Assignment 1: Setting up your test lab]]
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- [[#assignment-2][Assignment 2: Load tracepoint monitor program]]
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* XDP tracepoints
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The eBPF programs can be attached also to tracepoints. There are
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several tracepoints related to xdp:
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#+begin_example sh
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ls /sys/kernel/debug/tracing/events/xdp/
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xdp_cpumap_enqueue
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xdp_cpumap_kthread
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xdp_devmap_xmit
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xdp_exception
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xdp_redirect
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xdp_redirect_err
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xdp_redirect_map
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xdp_redirect_map_err
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#+end_example
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** Tracepoint program section
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The bpf library expects the tracepoint eBPF program to be stored
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in a section with following name:
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#+begin_example sh
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tracepoint/sys/tracepoint
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#+end_example
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where 'sys' is the tracepoint subsystem and 'tracepoint' is
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the tracepoint name.
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which can be done with following construct:
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#+begin_example sh
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SEC("tracepoint/xdp/xdp_exception")
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int trace_xdp_exception(struct xdp_exception_ctx *ctx)
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#+end_example
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** Tracepoint arguments
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There's single program pointer argument which points
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to the structure, that defines the tracepoint fields.
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Like for xdp:xdp_exception tracepoint:
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#+begin_example sh
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struct xdp_exception_ctx {
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__u64 __pad; // First 8 bytes are not accessible by bpf code
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__s32 prog_id; // offset:8; size:4; signed:1;
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__u32 act; // offset:12; size:4; signed:0;
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__s32 ifindex; // offset:16; size:4; signed:1;
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};
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int trace_xdp_exception(struct xdp_exception_ctx *ctx)
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#+end_example
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This struct is exported in tracepoint format file:
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#+begin_example sh
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# cat /sys/kernel/debug/tracing/events/xdp/xdp_exception/format
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...
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field:unsigned short common_type; offset:0; size:2; signed:0;
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field:unsigned char common_flags; offset:2; size:1; signed:0;
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field:unsigned char common_preempt_count; offset:3; size:1; signed:0;
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field:int common_pid; offset:4; size:4; signed:1;
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field:int prog_id; offset:8; size:4; signed:1;
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field:u32 act; offset:12; size:4; signed:0;
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field:int ifindex; offset:16; size:4; signed:1;
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...
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#+end_example
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** Tracepoint attaching
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To load a tracepoint program for this example we use following bpf
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library helper function:
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#+begin_example sh
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bpf_prog_load(cfg->filename, BPF_PROG_TYPE_TRACEPOINT, &obj, &bpf_fd))
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#+end_example
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It loads all the programs from the object together with maps and
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returns file descriptor of the first one.
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To attach the program to the tracepoint we need to create a tracepoint
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perf event and attach the eBPF program to it, using its file descriptor
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via PERF_EVENT_IOC_SET_BPF ioctl call:
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#+begin_example sh
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err = ioctl(fd, PERF_EVENT_IOC_SET_BPF, bpf_fd);
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#+end_example
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Please check trace_load_and_stats.c load_bpf_and_trace_attach function
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for all the details.
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* HASH map
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This example is using PERCPU HASH map, that stores number of aborted
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packets for interface
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#+begin_example sh
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struct bpf_map_def SEC("maps") xdp_stats_map = {
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.type = BPF_MAP_TYPE_PERCPU_HASH,
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.key_size = sizeof(__s32),
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.value_size = sizeof(__u64),
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.max_entries = 10,
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};
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#+end_example
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The interface is similar to the ARRAY map except that we need to specifically
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create new element in the hash if it does not exist:
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#+begin_example sh
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/* Lookup in kernel BPF-side returns pointer to actual data. */
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valp = bpf_map_lookup_elem(&xdp_stats_map, &key);
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/* If there's no record for interface, we need to create one,
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* with number of packets == 1
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*/
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if (!valp) {
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__u64 one = 1;
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return bpf_map_update_elem(&xdp_stats_map, &key, &one, 0) ? 1 : 0;
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}
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(*valp)++;
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#+end_example
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Please check trace_prog_kern.c for the full code.
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* Assignments
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** Assignment 1: Setting up your test lab
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In this lesson we will use the setup of the previous lesson:
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Basic02 - loading a program by name [[https://github.com/xdp-project/xdp-tutorial/tree/master/basic02-prog-by-name#assignment-2-add-xdp_abort-program]]
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and load XDP program from xdp_prog_kern.o that will abort every
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incoming packet:
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#+begin_example sh
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SEC("xdp_abort")
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int xdp_drop_func(struct xdp_md *ctx)
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{
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return XDP_ABORTED;
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}
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#+end_example
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with xdp_loader from previous lessson:
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Assignment 2: Add xdp_abort program [[https://github.com/xdp-project/xdp-tutorial/tree/master/basic02-prog-by-name#assignment-2-add-xdp_abort-program]]
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Setup the environment:
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#+begin_example sh
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$ sudo ../testenv/testenv.sh setup --name veth-basic02
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#+end_example
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Load the XDP program, tak produces aborted packets:
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#+begin_example sh
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$ sudo ../basic02-prog-by-name/xdp_loader --dev veth-basic02 --force --progsec xdp_abort
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#+end_example
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and make some packets:
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#+begin_example sh
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$ sudo ../testenv/testenv.sh enter --name veth-basic02
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# ping fc00:dead:cafe:1::1
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PING fc00:dead:cafe:1::1(fc00:dead:cafe:1::1) 56 data bytes
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#+end_example
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** Assignment 2: Load tracepoint monitor program
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Now when you run the trace_load_and_stats application it will
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load and attach the tracepoint eBPF program and display number
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of aborted packets per interface:
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#+begin_example
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# ./trace_load_and_stats
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Success: Loaded BPF-object(trace_prog_kern.o)
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Collecting stats from BPF map
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- BPF map (bpf_map_type:1) id:46 name:xdp_stats_map key_size:4 value_size:4 max_entries:10
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veth-basic02 (2)
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veth-basic02 (4)
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veth-basic02 (6)
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...
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#+end_example

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