From 60433a9d038db006ca2f49e3c5f050dc46aaad3a Mon Sep 17 00:00:00 2001 From: Dmitry Rokosov Date: Thu, 23 Nov 2023 10:19:43 +0300 Subject: samples: introduce new samples subdir for cgroup Patch series "samples: introduce cgroup events listeners", v3. To begin with, this patch series relocates the cgroup example code to the samples/cgroup directory, which is the appropriate location for such code snippets. Furthermore, a new memcg events listener is introduced. This listener is a simple yet effective tool for monitoring memory events and managing counter changes during runtime. Additionally, as per Andrew Morton's suggestion, a helpful reminder comment is included in the memcontrol implementation. This comment serves to ensure that the samples code is updated whenever new events are added. This patch (of 3): Move the cgroup_event_listener for cgroup v1 to the samples directory. This suggestion was proposed by Andrew Morton during the discussion [1]. Link: https://lore.kernel.org/all/20231106140934.3f5d4960141562fe8da53906@linux-foundation.org/ [1] Link: https://lkml.kernel.org/r/20231123071945.25811-1-ddrokosov@salutedevices.com Link: https://lkml.kernel.org/r/20231123071945.25811-2-ddrokosov@salutedevices.com Signed-off-by: Dmitry Rokosov Cc: Johannes Weiner Cc: Michal Hocko Cc: Muchun Song Cc: Roman Gushchin Cc: Shakeel Butt Signed-off-by: Andrew Morton --- samples/Kconfig | 6 +++ samples/Makefile | 1 + samples/cgroup/Makefile | 5 ++ samples/cgroup/cgroup_event_listener.c | 83 ++++++++++++++++++++++++++++++++++ 4 files changed, 95 insertions(+) create mode 100644 samples/cgroup/Makefile create mode 100644 samples/cgroup/cgroup_event_listener.c (limited to 'samples') diff --git a/samples/Kconfig b/samples/Kconfig index b0ddf5f36738..b288d9991d27 100644 --- a/samples/Kconfig +++ b/samples/Kconfig @@ -285,6 +285,12 @@ config SAMPLE_KMEMLEAK Build a sample program which have explicitly leaks memory to test kmemleak +config SAMPLE_CGROUP + bool "Build cgroup sample code" + depends on CGROUPS && CC_CAN_LINK && HEADERS_INSTALL + help + Build samples that demonstrate the usage of the cgroup API. + source "samples/rust/Kconfig" endif # SAMPLES diff --git a/samples/Makefile b/samples/Makefile index 0a551c2b33f4..b85fa64390c5 100644 --- a/samples/Makefile +++ b/samples/Makefile @@ -3,6 +3,7 @@ subdir-$(CONFIG_SAMPLE_AUXDISPLAY) += auxdisplay subdir-$(CONFIG_SAMPLE_ANDROID_BINDERFS) += binderfs +subdir-$(CONFIG_SAMPLE_CGROUP) += cgroup obj-$(CONFIG_SAMPLE_CONFIGFS) += configfs/ obj-$(CONFIG_SAMPLE_CONNECTOR) += connector/ obj-$(CONFIG_SAMPLE_FANOTIFY_ERROR) += fanotify/ diff --git a/samples/cgroup/Makefile b/samples/cgroup/Makefile new file mode 100644 index 000000000000..deef4530f5e7 --- /dev/null +++ b/samples/cgroup/Makefile @@ -0,0 +1,5 @@ +# SPDX-License-Identifier: GPL-2.0 + +userprogs-always-y += cgroup_event_listener + +userccflags += -I usr/include diff --git a/samples/cgroup/cgroup_event_listener.c b/samples/cgroup/cgroup_event_listener.c new file mode 100644 index 000000000000..3d70dc831a76 --- /dev/null +++ b/samples/cgroup/cgroup_event_listener.c @@ -0,0 +1,83 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * cgroup_event_listener.c - Simple listener of cgroup events + * + * Copyright (C) Kirill A. Shutemov + */ + +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#include + +#define USAGE_STR "Usage: cgroup_event_listener " + +int main(int argc, char **argv) +{ + int efd = -1; + int cfd = -1; + int event_control = -1; + char event_control_path[PATH_MAX]; + char line[LINE_MAX]; + int ret; + + if (argc != 3) + errx(1, "%s", USAGE_STR); + + cfd = open(argv[1], O_RDONLY); + if (cfd == -1) + err(1, "Cannot open %s", argv[1]); + + ret = snprintf(event_control_path, PATH_MAX, "%s/cgroup.event_control", + dirname(argv[1])); + if (ret >= PATH_MAX) + errx(1, "Path to cgroup.event_control is too long"); + + event_control = open(event_control_path, O_WRONLY); + if (event_control == -1) + err(1, "Cannot open %s", event_control_path); + + efd = eventfd(0, 0); + if (efd == -1) + err(1, "eventfd() failed"); + + ret = snprintf(line, LINE_MAX, "%d %d %s", efd, cfd, argv[2]); + if (ret >= LINE_MAX) + errx(1, "Arguments string is too long"); + + ret = write(event_control, line, strlen(line) + 1); + if (ret == -1) + err(1, "Cannot write to cgroup.event_control"); + + while (1) { + uint64_t result; + + ret = read(efd, &result, sizeof(result)); + if (ret == -1) { + if (errno == EINTR) + continue; + err(1, "Cannot read from eventfd"); + } + assert(ret == sizeof(result)); + + ret = access(event_control_path, W_OK); + if ((ret == -1) && (errno == ENOENT)) { + puts("The cgroup seems to have removed."); + break; + } + + if (ret == -1) + err(1, "cgroup.event_control is not accessible any more"); + + printf("%s %s: crossed\n", argv[1], argv[2]); + } + + return 0; +} -- cgit v1.2.3-59-g8ed1b