summaryrefslogtreecommitdiffstats
path: root/src/udev/udev-watch.c
blob: 58c82794f0f8384ab1c984fd5e6803f4d9819965 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
/* SPDX-License-Identifier: GPL-2.0-or-later */
/*
 * Copyright © 2009 Canonical Ltd.
 * Copyright © 2009 Scott James Remnant <scott@netsplit.com>
 */

#include <sys/inotify.h>

#include "alloc-util.h"
#include "device-private.h"
#include "device-util.h"
#include "dirent-util.h"
#include "fd-util.h"
#include "fs-util.h"
#include "mkdir.h"
#include "parse-util.h"
#include "rm-rf.h"
#include "stdio-util.h"
#include "string-util.h"
#include "udev-util.h"
#include "udev-watch.h"

int device_new_from_watch_handle_at(sd_device **ret, int dirfd, int wd) {
        char path_wd[STRLEN("/run/udev/watch/") + DECIMAL_STR_MAX(int)];
        _cleanup_free_ char *id = NULL;
        int r;

        assert(ret);

        if (wd < 0)
                return -EBADF;

        if (dirfd >= 0) {
                xsprintf(path_wd, "%d", wd);
                r = readlinkat_malloc(dirfd, path_wd, &id);
        } else {
                xsprintf(path_wd, "/run/udev/watch/%d", wd);
                r = readlink_malloc(path_wd, &id);
        }
        if (r < 0)
                return r;

        return sd_device_new_from_device_id(ret, id);
}

int udev_watch_restore(int inotify_fd) {
        _cleanup_closedir_ DIR *dir = NULL;
        int r;

        /* Move any old watches directory out of the way, and then restore the watches. */

        assert(inotify_fd >= 0);

        (void) rm_rf("/run/udev/watch.old", REMOVE_ROOT);

        if (rename("/run/udev/watch", "/run/udev/watch.old") < 0) {
                if (errno == ENOENT)
                        return 0;

                r = log_warning_errno(errno,
                                      "Failed to move watches directory '/run/udev/watch/'. "
                                      "Old watches will not be restored: %m");
                goto finalize;
        }

        dir = opendir("/run/udev/watch.old");
        if (!dir) {
                r = log_warning_errno(errno,
                                      "Failed to open old watches directory '/run/udev/watch.old/'. "
                                      "Old watches will not be restored: %m");
                goto finalize;
        }

        FOREACH_DIRENT_ALL(de, dir, break) {
                _cleanup_(sd_device_unrefp) sd_device *dev = NULL;
                int wd;

                /* For backward compatibility, read symlink from watch handle to device ID. This is necessary
                 * when udevd is restarted after upgrading from v248 or older. The new format (ID -> wd) was
                 * introduced by e7f781e473f5119bf9246208a6de9f6b76a39c5d (v249). */

                if (dot_or_dot_dot(de->d_name))
                        continue;

                if (safe_atoi(de->d_name, &wd) < 0)
                        continue;

                r = device_new_from_watch_handle_at(&dev, dirfd(dir), wd);
                if (r < 0) {
                        log_full_errno(r == -ENODEV ? LOG_DEBUG : LOG_WARNING, r,
                                       "Failed to create sd_device object from saved watch handle '%i', ignoring: %m",
                                       wd);
                        continue;
                }

                (void) udev_watch_begin(inotify_fd, dev);
        }

        r = 0;

finalize:
        (void) rm_rf("/run/udev/watch.old", REMOVE_ROOT);
        return r;
}

static int udev_watch_clear(sd_device *dev, int dirfd, int *ret_wd) {
        _cleanup_free_ char *wd_str = NULL, *buf = NULL;
        const char *id;
        int wd = -1, r;

        assert(dev);
        assert(dirfd >= 0);

        r = device_get_device_id(dev, &id);
        if (r < 0)
                return log_device_debug_errno(dev, r, "Failed to get device ID: %m");

        /* 1. read symlink ID -> wd */
        r = readlinkat_malloc(dirfd, id, &wd_str);
        if (r == -ENOENT) {
                if (ret_wd)
                        *ret_wd = -1;
                return 0;
        }
        if (r < 0) {
                log_device_debug_errno(dev, r, "Failed to read symlink '/run/udev/watch/%s': %m", id);
                goto finalize;
        }

        r = safe_atoi(wd_str, &wd);
        if (r < 0) {
                log_device_debug_errno(dev, r, "Failed to parse watch handle from symlink '/run/udev/watch/%s': %m", id);
                goto finalize;
        }

        if (wd < 0) {
                r = log_device_debug_errno(dev, SYNTHETIC_ERRNO(EBADF), "Invalid watch handle %i.", wd);
                goto finalize;
        }

        /* 2. read symlink wd -> ID */
        r = readlinkat_malloc(dirfd, wd_str, &buf);
        if (r < 0) {
                log_device_debug_errno(dev, r, "Failed to read symlink '/run/udev/watch/%s': %m", wd_str);
                goto finalize;
        }

        /* 3. check if the symlink wd -> ID is owned by the device. */
        if (!streq(buf, id)) {
                r = log_device_debug_errno(dev, SYNTHETIC_ERRNO(ENOENT),
                                           "Symlink '/run/udev/watch/%s' is owned by another device '%s'.", wd_str, buf);
                goto finalize;
        }

        /* 4. remove symlink wd -> ID.
         * In the above, we already confirmed that the symlink is owned by us. Hence, no other workers remove
         * the symlink and cannot create a new symlink with the same filename but to a different ID. Hence,
         * the removal below is safe even the steps in this function are not atomic. */
        if (unlinkat(dirfd, wd_str, 0) < 0 && errno != ENOENT)
                log_device_debug_errno(dev, errno, "Failed to remove '/run/udev/watch/%s', ignoring: %m", wd_str);

        if (ret_wd)
                *ret_wd = wd;
        r = 0;

finalize:
        /* 5. remove symlink ID -> wd.
         * The file is always owned by the device. Hence, it is safe to remove it unconditionally. */
        if (unlinkat(dirfd, id, 0) < 0 && errno != ENOENT)
                log_device_debug_errno(dev, errno, "Failed to remove '/run/udev/watch/%s': %m", id);

        return r;
}

int udev_watch_begin(int inotify_fd, sd_device *dev) {
        char wd_str[DECIMAL_STR_MAX(int)];
        _cleanup_close_ int dirfd = -EBADF;
        const char *devnode, *id;
        int wd, r;

        assert(inotify_fd >= 0);
        assert(dev);

        if (device_for_action(dev, SD_DEVICE_REMOVE))
                return 0;

        r = sd_device_get_devname(dev, &devnode);
        if (r < 0)
                return log_device_debug_errno(dev, r, "Failed to get device node: %m");

        r = device_get_device_id(dev, &id);
        if (r < 0)
                return log_device_debug_errno(dev, r, "Failed to get device ID: %m");

        r = dirfd = open_mkdir_at(AT_FDCWD, "/run/udev/watch", O_CLOEXEC | O_RDONLY, 0755);
        if (r < 0)
                return log_device_debug_errno(dev, r, "Failed to create and open '/run/udev/watch/': %m");

        /* 1. Clear old symlinks */
        (void) udev_watch_clear(dev, dirfd, NULL);

        /* 2. Add inotify watch */
        log_device_debug(dev, "Adding watch on '%s'", devnode);
        wd = inotify_add_watch(inotify_fd, devnode, IN_CLOSE_WRITE);
        if (wd < 0)
                return log_device_debug_errno(dev, errno, "Failed to watch device node '%s': %m", devnode);

        xsprintf(wd_str, "%d", wd);

        /* 3. Create new symlinks */
        if (symlinkat(wd_str, dirfd, id) < 0) {
                r = log_device_debug_errno(dev, errno, "Failed to create symlink '/run/udev/watch/%s' to '%s': %m", id, wd_str);
                goto on_failure;
        }

        if (symlinkat(id, dirfd, wd_str) < 0) {
                /* Possibly, the watch handle is previously assigned to another device, and udev_watch_end()
                 * is not called for the device yet. */
                r = log_device_debug_errno(dev, errno, "Failed to create symlink '/run/udev/watch/%s' to '%s': %m", wd_str, id);
                goto on_failure;
        }

        return 0;

on_failure:
        (void) unlinkat(dirfd, id, 0);
        (void) inotify_rm_watch(inotify_fd, wd);
        return r;
}

int udev_watch_end(int inotify_fd, sd_device *dev) {
        _cleanup_close_ int dirfd = -EBADF;
        int wd, r;

        assert(dev);

        /* This may be called by 'udevadm test'. In that case, inotify_fd is not initialized. */
        if (inotify_fd < 0)
                return 0;

        if (sd_device_get_devname(dev, NULL) < 0)
                return 0;

        dirfd = RET_NERRNO(open("/run/udev/watch", O_CLOEXEC | O_DIRECTORY | O_NOFOLLOW | O_RDONLY));
        if (dirfd == -ENOENT)
                return 0;
        if (dirfd < 0)
                return log_device_debug_errno(dev, dirfd, "Failed to open '/run/udev/watch/': %m");

        /* First, clear symlinks. */
        r = udev_watch_clear(dev, dirfd, &wd);
        if (r < 0)
                return r;

        /* Then, remove inotify watch. */
        log_device_debug(dev, "Removing watch handle %i.", wd);
        (void) inotify_rm_watch(inotify_fd, wd);

        return 0;
}