// SPDX-License-Identifier: GPL-2.0
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/*
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* cgroup_event_listener.c - Simple listener of cgroup events
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*
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* Copyright (C) Kirill A. Shutemov <kirill@shutemov.name>
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*/
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#include <assert.h>
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#include <err.h>
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#include <errno.h>
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#include <fcntl.h>
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#include <libgen.h>
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#include <limits.h>
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#include <stdio.h>
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#include <string.h>
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#include <unistd.h>
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#include <sys/eventfd.h>
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#define USAGE_STR "Usage: cgroup_event_listener <path-to-control-file> <args>"
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int main(int argc, char **argv)
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{
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int efd = -1;
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int cfd = -1;
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int event_control = -1;
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char event_control_path[PATH_MAX];
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char line[LINE_MAX];
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int ret;
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if (argc != 3)
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errx(1, "%s", USAGE_STR);
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cfd = open(argv[1], O_RDONLY);
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if (cfd == -1)
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err(1, "Cannot open %s", argv[1]);
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ret = snprintf(event_control_path, PATH_MAX, "%s/cgroup.event_control",
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dirname(argv[1]));
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if (ret >= PATH_MAX)
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errx(1, "Path to cgroup.event_control is too long");
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event_control = open(event_control_path, O_WRONLY);
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if (event_control == -1)
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err(1, "Cannot open %s", event_control_path);
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efd = eventfd(0, 0);
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if (efd == -1)
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err(1, "eventfd() failed");
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ret = snprintf(line, LINE_MAX, "%d %d %s", efd, cfd, argv[2]);
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if (ret >= LINE_MAX)
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errx(1, "Arguments string is too long");
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ret = write(event_control, line, strlen(line) + 1);
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if (ret == -1)
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err(1, "Cannot write to cgroup.event_control");
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while (1) {
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uint64_t result;
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ret = read(efd, &result, sizeof(result));
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if (ret == -1) {
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if (errno == EINTR)
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continue;
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err(1, "Cannot read from eventfd");
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}
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assert(ret == sizeof(result));
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ret = access(event_control_path, W_OK);
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if ((ret == -1) && (errno == ENOENT)) {
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puts("The cgroup seems to have removed.");
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break;
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}
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if (ret == -1)
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err(1, "cgroup.event_control is not accessible any more");
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printf("%s %s: crossed\n", argv[1], argv[2]);
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}
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return 0;
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}
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