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/*
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 * udev-kvm-check.c
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 *
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 * Copyright 2018 Red Hat, Inc.
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 *
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 * This is free software; you can redistribute it and/or modify it
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 * under the terms of the GNU General Public License as published by
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 * the Free Software Foundation; either version 2 of the License, or
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 * (at your option) any later version.
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 *
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 * This program is distributed in the hope that it will be useful, but
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 * WITHOUT ANY WARRANTY; without even the implied warranty of
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 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
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 * General Public License for more details.
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 *
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 * You should have received a copy of the GNU General Public License
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 * along with this program; if not, write to the Free Software Foundation,
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 * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
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 *
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 */
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#include <ctype.h>
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#include <syslog.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#define DEFAULT 0
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#define FACILITY "kvm"
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#define SYSCONFIG_KVM "/etc/sysconfig/kvm"
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#define COUNT_MSG \
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    "%d %s now active"
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#define SUBSCRIPTION_MSG \
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    "%d %s now active; your Red Hat Enterprise Linux subscription" \
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    " limit is %d guests. Please review your Red Hat Enterprise Linux" \
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    " subscription agreement or contact your Red Hat" \
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    " support representative for more information. You" \
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    " may review the Red Hat Enterprise subscription" \
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    " limits at http://www.redhat.com/rhel-virt-limits"
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int get_threshold_from_file(FILE *fp)
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{
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    static const char key[] = "THRESHOLD=";
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    int pos = 0;
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    int thres;
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    int ch;
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start:
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    /* State START - at beginning of line, search for beginning of "THRESHOLD="
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     * string.
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     */
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    ch = getc(fp);
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    if (ch == EOF) {
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        return DEFAULT;
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    }
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    if (isspace(ch)) {
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        goto start;
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    }
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    if (ch == 'T') {
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        pos = 1;
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        goto key;
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    }
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    goto eol;
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eol:
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    /* State EOL - loop until end of line */
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    ch = getc(fp);
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    if (ch == EOF) {
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        return DEFAULT;
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    }
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    if (ch == '\n') {
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        goto start;
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    }
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    goto eol;
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key:
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    /* State KEY - match "THRESHOLD=" string, go to THRESHOLD if found */
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    ch = getc(fp);
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    if (ch == EOF) {
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        return DEFAULT;
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    }
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    if (ch == key[pos]) {
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        pos++;
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        if (key[pos] == 0) {
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            goto threshold;
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        } else {
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            goto key;
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        }
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    }
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    goto eol;
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threshold:
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    /* State THRESHOLD - parse number using fscanf, expect comment or space
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     * or EOL.
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     */
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    ch = getc(fp);
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    if (ch == EOF) {
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        return DEFAULT;
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    }
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    if (!isdigit(ch)) {
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        goto eol;
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    }
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    ungetc(ch, fp);
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    if (fscanf(fp, "%d", &thres) != 1) {
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        return DEFAULT;
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    }
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    ch = getc(fp);
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    if (ch == '#' || ch == EOF || ch == '\n' || isspace(ch)) {
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        return thres;
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    }
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    goto eol;
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}
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int get_threshold()
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{
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    FILE *fp = fopen(SYSCONFIG_KVM, "r");
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    int val;
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    if (!fp) {
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        return DEFAULT;
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    }
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    val = get_threshold_from_file(fp);
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    fclose (fp);
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    return val;
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}
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const char *guest(int count)
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{
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    return (count == 1 ? "guest" : "guests");
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}
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void emit_count_message(int count)
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{
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    openlog(FACILITY, LOG_CONS, LOG_USER);
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    syslog(LOG_INFO, COUNT_MSG, count, guest(count));
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    closelog();
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}
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void emit_subscription_message(int count, int threshold)
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{
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    openlog(FACILITY, LOG_CONS, LOG_USER);
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    syslog(LOG_WARNING, SUBSCRIPTION_MSG, count, guest(count), threshold);
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    closelog();
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}
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int main(int argc, char **argv)
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{
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    int count, threshold;
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    if (argc < 3)
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        exit(1);
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    count = atoi(argv[1]);
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    threshold = get_threshold();
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    if (!strcmp(argv[2], "create")) {
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        if (threshold == 0) {
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            emit_count_message(count);
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        } else if (count > threshold) {
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            emit_subscription_message(count, threshold);
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        }
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    } else {
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        if (count >= threshold) {
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            emit_count_message(count);
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        }
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    }
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    return 0;
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}