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selftests/bpf: Tests using sleepable tracepoints to monitor cgroup events
Tests the functionalities of sleepable tracing prog, sleepable tracepoints (i.e. cgroup_mkdir_s and cgroup_rmdir_s) and cgroup iter prog all together. The added selftest resembles a real-world application, where bpf is used to export cgroup-level performance stats. There are two sets of progs in the test: cgroup_monitor and cgroup_sched_lat - Cgroup_monitor monitors cgroup creation and deletion using sleepable tracing; for each cgroup created, creates a directory in bpffs; creates a cgroup iter link and pins it in that directory. - Cgroup_sched_lat is the program that collects cgroup's scheduling latencies and store them in hash map. Cgroup_sched_lat implements a cgroup iter prog, which reads the stats from the map and seq_prints them. This cgroup iter prog is the prog pinned by cgroup_monitor in each bpffs directory. The cgroup_sched_lat in this test can be adapted for exporting similar cgroup-level performance stats. Signed-off-by: Hao Luo <haoluo@google.com>
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‎tools/testing/selftests/bpf/prog_tests/test_cgroup_stats.c‎

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// SPDX-License-Identifier: GPL-2.0
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/* Copyright (c) 2022 Google */
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#define _GNU_SOURCE
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#include <sys/stat.h> /* mkdir */
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#include <fcntl.h> /* name_to_handle_at */
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#include <stdlib.h>
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#include <test_progs.h>
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#include "cgroup_monitor.skel.h"
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#include "cgroup_sched_lat.skel.h"
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static char mkdir_prog_path[64];
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static char rmdir_prog_path[64];
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static char dump_prog_path[64];
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/* Get cgroup id from a full path to cgroup */
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static int get_cgroup_id(const char *cgroup)
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{
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int mount_id = 0;
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struct {
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struct file_handle fh;
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__u64 cgid;
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} fh = {};
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fh.fh.handle_bytes = sizeof(fh.cgid);
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if (name_to_handle_at(AT_FDCWD, cgroup, &fh.fh, &mount_id, 0))
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return -1;
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return fh.cgid;
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}
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static void spin_on_cpu(int seconds)
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{
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time_t start, now;
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start = time(NULL);
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do {
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now = time(NULL);
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} while (now - start < seconds);
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}
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static void do_work(const char *cgroup)
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{
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int i, cpu = 0, pid;
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char cmd[128];
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/* make cgroup threaded */
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snprintf(cmd, 128, "echo threaded > %s/cgroup.type", cgroup);
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system(cmd);
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/* try to enable cpu controller. this may fail if cpu controller is not
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* available in cgroup.controllers or there is a cgroup v1 already
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* mounted in the system.
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*/
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snprintf(cmd, 128, "echo \"+cpu\" > %s/cgroup.subtree_control", cgroup);
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system(cmd);
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/* launch two children, both running in child cgroup */
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for (i = 0; i < 2; ++i) {
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pid = fork();
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if (pid == 0) {
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/* attach to cgroup */
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snprintf(cmd, 128, "echo %d > %s/cgroup.procs", getpid(), cgroup);
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system(cmd);
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/* pin process to target cpu */
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snprintf(cmd, 128, "taskset -pc %d %d", cpu, getpid());
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system(cmd);
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spin_on_cpu(3); /* spin on cpu for 3 seconds */
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exit(0);
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}
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}
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/* pin parent process to target cpu */
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snprintf(cmd, 128, "taskset -pc %d %d", cpu, getpid());
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system(cmd);
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spin_on_cpu(3); /* spin on cpu for 3 seconds */
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wait(NULL);
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}
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/* Check reading cgroup stats from auto pinned objects
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* @root: root directory in bpffs set up for this test
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* @cgroup: cgroup path
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*/
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static void check_cgroup_stats(const char *root, const char *cgroup)
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{
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unsigned long queue_self, queue_other;
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char buf[64], path[64];
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int id, cgroup_id;
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FILE *file;
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id = get_cgroup_id(cgroup);
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if (!ASSERT_GE(id, 0, "get_cgroup_id"))
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return;
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snprintf(path, sizeof(path), "%s/%d/stats", root, id);
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file = fopen(path, "r");
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if (!ASSERT_OK_PTR(file, "open"))
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return;
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ASSERT_OK_PTR(fgets(buf, sizeof(buf), file), "cat");
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ASSERT_EQ(sscanf(buf, "cgroup_id: %8d", &cgroup_id), 1, "output");
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ASSERT_EQ(id, cgroup_id, "cgroup_id");
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ASSERT_OK_PTR(fgets(buf, sizeof(buf), file), "cat");
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ASSERT_EQ(sscanf(buf, "queue_self: %8lu", &queue_self), 1, "output");
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ASSERT_OK_PTR(fgets(buf, sizeof(buf), file), "cat");
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ASSERT_EQ(sscanf(buf, "queue_other: %8lu", &queue_other), 1, "output");
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fclose(file);
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}
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/* Set up bpf progs for monitoring cgroup activities. */
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static void setup_cgroup_monitor(const char *root)
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{
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struct cgroup_monitor *skel = NULL;
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skel = cgroup_monitor__open_and_load();
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if (!ASSERT_OK_PTR(skel, "cgroup_monitor_skel_load"))
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return;
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cgroup_monitor__attach(skel);
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snprintf(skel->bss->root, sizeof(skel->bss->root), "%s", root);
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snprintf(mkdir_prog_path, 64, "%s/mkdir_prog", root);
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bpf_obj_pin(bpf_link__fd(skel->links.mkdir_prog), mkdir_prog_path);
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snprintf(rmdir_prog_path, 64, "%s/rmdir_prog", root);
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bpf_obj_pin(bpf_link__fd(skel->links.rmdir_prog), rmdir_prog_path);
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cgroup_monitor__destroy(skel);
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}
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void test_cgroup_stats(void)
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{
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char bpf_tmpl[] = "/sys/fs/bpf/XXXXXX";
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char cgrp_tmpl[] = "/sys/fs/cgroup/XXXXXX";
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struct cgroup_sched_lat *skel = NULL;
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char *root, *cgroup;
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/* prepare test directories */
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system("mount -t cgroup2 none /sys/fs/cgroup");
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system("mount -t bpf bpffs /sys/fs/bpf");
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root = mkdtemp(bpf_tmpl);
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chmod(root, 0777);
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/* set up progs for monitoring cgroup events */
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setup_cgroup_monitor(root);
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/* set up progs for profiling cgroup stats */
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skel = cgroup_sched_lat__open_and_load();
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if (!ASSERT_OK_PTR(skel, "cgroup_sched_lat_skel_load"))
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goto cleanup_root;
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snprintf(dump_prog_path, 64, "%s/prog", root);
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bpf_obj_pin(bpf_program__fd(skel->progs.dump_cgroup), dump_prog_path);
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chmod(dump_prog_path, 0644);
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cgroup_sched_lat__attach(skel);
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/* thanks to cgroup monitoring progs, a directory corresponding to the
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* cgroup is created in bpffs.
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*/
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cgroup = mkdtemp(cgrp_tmpl);
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/* collect some cgroup-level stats and check reading them from bpffs */
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do_work(cgroup);
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check_cgroup_stats(root, cgroup);
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/* thanks to cgroup monitoring progs, removing cgroups also removes
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* the created directory in bpffs.
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*/
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rmdir(cgroup);
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/* clean up cgroup monitoring progs */
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cgroup_sched_lat__detach(skel);
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cgroup_sched_lat__destroy(skel);
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unlink(dump_prog_path);
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cleanup_root:
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/* remove test directories in bpffs */
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unlink(mkdir_prog_path);
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unlink(rmdir_prog_path);
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rmdir(root);
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return;
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}

‎tools/testing/selftests/bpf/progs/bpf_iter.h‎

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@@ -16,6 +16,7 @@
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#define bpf_iter__bpf_map_elem bpf_iter__bpf_map_elem___not_used
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#define bpf_iter__bpf_sk_storage_map bpf_iter__bpf_sk_storage_map___not_used
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#define bpf_iter__sockmap bpf_iter__sockmap___not_used
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#define bpf_iter__cgroup bpf_iter__cgroup__not_used
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#define btf_ptr btf_ptr___not_used
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#define BTF_F_COMPACT BTF_F_COMPACT___not_used
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#define BTF_F_NONAME BTF_F_NONAME___not_used
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#undef bpf_iter__bpf_map_elem
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#undef bpf_iter__bpf_sk_storage_map
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#undef bpf_iter__sockmap
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#undef bpf_iter__cgroup
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#undef btf_ptr
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#undef BTF_F_COMPACT
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#undef BTF_F_NONAME
@@ -132,6 +134,11 @@ struct bpf_iter__sockmap {
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struct sock *sk;
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};
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struct bpf_iter__cgroup {
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struct bpf_iter_meta *meta;
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struct cgroup *cgroup;
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} __attribute__((preserve_access_index));
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struct btf_ptr {
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void *ptr;
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__u32 type_id;

‎tools/testing/selftests/bpf/progs/cgroup_monitor.c‎

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// SPDX-License-Identifier: GPL-2.0
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/* Copyright (c) 2022 Google */
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#include "vmlinux.h"
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#include <bpf/bpf_helpers.h>
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#include <bpf/bpf_tracing.h>
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char _license[] SEC("license") = "GPL";
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/* root is the directory path. */
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char root[64];
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SEC("tp_btf.s/cgroup_mkdir_s")
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int BPF_PROG(mkdir_prog, struct cgroup *cgrp)
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{
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static char dirname[64];
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static char prog_path[64];
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static char iter_path[64];
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static union bpf_iter_link_info info;
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static union bpf_attr get_attr;
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static union bpf_attr link_attr;
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static union bpf_attr pin_attr;
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int link_fd, prog_fd, ret;
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__u64 id;
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/* create directory in bpffs named by cgroup's id. */
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id = cgrp->kn->id;
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BPF_SNPRINTF(dirname, sizeof(dirname), "%s/%lu", root, id);
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ret = bpf_mkdir(dirname, sizeof(dirname), 0755);
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if (ret)
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return ret;
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/* get cgroup iter prog pinned by test progs. */
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BPF_SNPRINTF(prog_path, sizeof(prog_path), "%s/prog", root);
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get_attr.bpf_fd = 0;
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get_attr.pathname = (__u64)prog_path;
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get_attr.file_flags = BPF_F_RDONLY;
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prog_fd = bpf_sys_bpf(BPF_OBJ_GET, &get_attr, sizeof(get_attr));
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if (prog_fd < 0)
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return prog_fd;
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/* create a link, parameterized by cgroup id. */
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info.cgroup.cgroup_id = id;
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link_attr.link_create.prog_fd = prog_fd;
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link_attr.link_create.attach_type = BPF_TRACE_ITER;
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link_attr.link_create.target_fd = 0;
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link_attr.link_create.flags = 0;
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link_attr.link_create.iter_info = (__u64)&info;
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link_attr.link_create.iter_info_len = sizeof(info);
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ret = bpf_sys_bpf(BPF_LINK_CREATE, &link_attr, sizeof(link_attr));
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if (ret < 0) {
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bpf_sys_close(prog_fd);
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return ret;
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}
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link_fd = ret;
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/* pin the link in the created directory */
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BPF_SNPRINTF(iter_path, sizeof(iter_path), "%s/stats", dirname);
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pin_attr.pathname = (__u64)iter_path;
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pin_attr.bpf_fd = link_fd;
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pin_attr.file_flags = 0;
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ret = bpf_sys_bpf(BPF_OBJ_PIN, &pin_attr, sizeof(pin_attr));
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bpf_sys_close(prog_fd);
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bpf_sys_close(link_fd);
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return ret;
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}
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SEC("tp_btf.s/cgroup_rmdir_s")
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int BPF_PROG(rmdir_prog, struct cgroup *cgrp)
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{
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static char dirname[64];
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static char path[64];
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BPF_SNPRINTF(dirname, sizeof(dirname), "%s/%lu", root, cgrp->kn->id);
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BPF_SNPRINTF(path, sizeof(path), "%s/stats", dirname);
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bpf_unlink(path, sizeof(path));
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return bpf_rmdir(dirname, sizeof(dirname));
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}

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