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authorDmitry Rokosov <ddrokosov@salutedevices.com>2023-11-23 10:19:43 +0300
committerAndrew Morton <akpm@linux-foundation.org>2023-12-10 16:51:54 -0800
commit60433a9d038db006ca2f49e3c5f050dc46aaad3a (patch)
treef190f13df50a5679591cf43b10907e41af869918 /samples
parentebc20dcac4ce98f227f63cf8be0c9c1152d25cc9 (diff)
downloadlwn-60433a9d038db006ca2f49e3c5f050dc46aaad3a.tar.gz
lwn-60433a9d038db006ca2f49e3c5f050dc46aaad3a.zip
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 <ddrokosov@salutedevices.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Muchun Song <muchun.song@linux.dev> Cc: Roman Gushchin <roman.gushchin@linux.dev> Cc: Shakeel Butt <shakeelb@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'samples')
-rw-r--r--samples/Kconfig6
-rw-r--r--samples/Makefile1
-rw-r--r--samples/cgroup/Makefile5
-rw-r--r--samples/cgroup/cgroup_event_listener.c83
4 files changed, 95 insertions, 0 deletions
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 <kirill@shutemov.name>
+ */
+
+#include <assert.h>
+#include <err.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <libgen.h>
+#include <limits.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+#include <sys/eventfd.h>
+
+#define USAGE_STR "Usage: cgroup_event_listener <path-to-control-file> <args>"
+
+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;
+}