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![David Howells](/assets/img/avatar_default.png)
Add handling for loss of notifications by having read() insert a loss-notification message after it has read the pipe buffer that was last in the ring when the loss occurred. Lossage can come about either by running out of notification descriptors or by running out of space in the pipe ring. Signed-off-by: David Howells <dhowells@redhat.com>
186 lines
3.9 KiB
C
186 lines
3.9 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/* Use /dev/watch_queue to watch for notifications.
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*
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* Copyright (C) 2020 Red Hat, Inc. All Rights Reserved.
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* Written by David Howells (dhowells@redhat.com)
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*/
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#define _GNU_SOURCE
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#include <stdbool.h>
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#include <stdarg.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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#include <signal.h>
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#include <unistd.h>
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#include <errno.h>
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#include <sys/ioctl.h>
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#include <limits.h>
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#include <linux/watch_queue.h>
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#include <linux/unistd.h>
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#include <linux/keyctl.h>
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#ifndef KEYCTL_WATCH_KEY
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#define KEYCTL_WATCH_KEY -1
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#endif
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#ifndef __NR_keyctl
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#define __NR_keyctl -1
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#endif
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#define BUF_SIZE 256
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static long keyctl_watch_key(int key, int watch_fd, int watch_id)
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{
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return syscall(__NR_keyctl, KEYCTL_WATCH_KEY, key, watch_fd, watch_id);
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}
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static const char *key_subtypes[256] = {
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[NOTIFY_KEY_INSTANTIATED] = "instantiated",
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[NOTIFY_KEY_UPDATED] = "updated",
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[NOTIFY_KEY_LINKED] = "linked",
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[NOTIFY_KEY_UNLINKED] = "unlinked",
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[NOTIFY_KEY_CLEARED] = "cleared",
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[NOTIFY_KEY_REVOKED] = "revoked",
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[NOTIFY_KEY_INVALIDATED] = "invalidated",
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[NOTIFY_KEY_SETATTR] = "setattr",
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};
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static void saw_key_change(struct watch_notification *n, size_t len)
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{
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struct key_notification *k = (struct key_notification *)n;
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if (len != sizeof(struct key_notification)) {
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fprintf(stderr, "Incorrect key message length\n");
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return;
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}
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printf("KEY %08x change=%u[%s] aux=%u\n",
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k->key_id, n->subtype, key_subtypes[n->subtype], k->aux);
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}
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/*
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* Consume and display events.
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*/
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static void consumer(int fd)
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{
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unsigned char buffer[433], *p, *end;
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union {
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struct watch_notification n;
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unsigned char buf1[128];
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} n;
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ssize_t buf_len;
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for (;;) {
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buf_len = read(fd, buffer, sizeof(buffer));
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if (buf_len == -1) {
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perror("read");
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exit(1);
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}
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if (buf_len == 0) {
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printf("-- END --\n");
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return;
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}
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if (buf_len > sizeof(buffer)) {
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fprintf(stderr, "Read buffer overrun: %zd\n", buf_len);
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return;
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}
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printf("read() = %zd\n", buf_len);
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p = buffer;
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end = buffer + buf_len;
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while (p < end) {
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size_t largest, len;
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largest = end - p;
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if (largest > 128)
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largest = 128;
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if (largest < sizeof(struct watch_notification)) {
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fprintf(stderr, "Short message header: %zu\n", largest);
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return;
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}
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memcpy(&n, p, largest);
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printf("NOTIFY[%03zx]: ty=%06x sy=%02x i=%08x\n",
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p - buffer, n.n.type, n.n.subtype, n.n.info);
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len = n.n.info & WATCH_INFO_LENGTH;
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if (len < sizeof(n.n) || len > largest) {
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fprintf(stderr, "Bad message length: %zu/%zu\n", len, largest);
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exit(1);
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}
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switch (n.n.type) {
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case WATCH_TYPE_META:
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switch (n.n.subtype) {
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case WATCH_META_REMOVAL_NOTIFICATION:
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printf("REMOVAL of watchpoint %08x\n",
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(n.n.info & WATCH_INFO_ID) >>
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WATCH_INFO_ID__SHIFT);
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break;
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case WATCH_META_LOSS_NOTIFICATION:
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printf("-- LOSS --\n");
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break;
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default:
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printf("other meta record\n");
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break;
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}
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break;
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case WATCH_TYPE_KEY_NOTIFY:
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saw_key_change(&n.n, len);
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break;
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default:
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printf("other type\n");
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break;
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}
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p += len;
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}
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}
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}
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static struct watch_notification_filter filter = {
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.nr_filters = 1,
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.filters = {
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[0] = {
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.type = WATCH_TYPE_KEY_NOTIFY,
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.subtype_filter[0] = UINT_MAX,
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},
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},
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};
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int main(int argc, char **argv)
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{
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int pipefd[2], fd;
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if (pipe2(pipefd, O_NOTIFICATION_PIPE) == -1) {
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perror("pipe2");
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exit(1);
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}
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fd = pipefd[0];
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if (ioctl(fd, IOC_WATCH_QUEUE_SET_SIZE, BUF_SIZE) == -1) {
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perror("watch_queue(size)");
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exit(1);
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}
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if (ioctl(fd, IOC_WATCH_QUEUE_SET_FILTER, &filter) == -1) {
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perror("watch_queue(filter)");
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exit(1);
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}
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if (keyctl_watch_key(KEY_SPEC_SESSION_KEYRING, fd, 0x01) == -1) {
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perror("keyctl");
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exit(1);
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}
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if (keyctl_watch_key(KEY_SPEC_USER_KEYRING, fd, 0x02) == -1) {
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perror("keyctl");
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exit(1);
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}
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consumer(fd);
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exit(0);
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}
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