src/libudev/libudev-queue-private.c

   1 /*
   2  * libudev - interface to udev device information
   3  *
   4  * Copyright (C) 2008 Kay Sievers <kay.sievers@vrfy.org>
   5  * Copyright (C) 2009 Alan Jenkins <alan-jenkins@tuffmail.co.uk>
   6  *
   7  * This library is free software; you can redistribute it and/or
   8  * modify it under the terms of the GNU Lesser General Public
   9  * License as published by the Free Software Foundation; either
  10  * version 2.1 of the License, or (at your option) any later version.
  11  */
  12
  13 /*
  14  * DISCLAIMER - The file format mentioned here is private to udev/libudev,
  15  *              and may be changed without notice.
  16  *
  17  * The udev event queue is exported as a binary log file.
  18  * Each log record consists of a sequence number followed by the device path.
  19  *
  20  * When a new event is queued, its details are appended to the log.
  21  * When the event finishes, a second record is appended to the log
  22  * with the same sequence number but a devpath len of 0.
  23  *
  24  * Example:
  25  *        { 0x0000000000000001 }
  26  *        { 0x0000000000000001, 0x0019, "/devices/virtual/mem/null" },
  27  *        { 0x0000000000000002, 0x001b, "/devices/virtual/mem/random" },
  28  *        { 0x0000000000000001, 0x0000 },
  29  *        { 0x0000000000000003, 0x0019, "/devices/virtual/mem/zero" },
  30  *
  31  * Events 2 and 3 are still queued, but event 1 has finished.
  32  *
  33  * The queue does not grow indefinitely. It is periodically re-created
  34  * to remove finished events. Atomic rename() makes this transparent to readers.
  35  *
  36  * The queue file starts with a single sequence number which specifies the
  37  * minimum sequence number in the log that follows. Any events prior to this
  38  * sequence number have already finished.
  39  */
  40
  41 #include <stdio.h>
  42 #include <stdlib.h>
  43 #include <string.h>
  44 #include <unistd.h>
  45 #include <fcntl.h>
  46 #include <dirent.h>
  47 #include <limits.h>
  48 #include <errno.h>
  49 #include <sys/stat.h>
  50 #include <sys/types.h>
  51
  52 #include "libudev.h"
  53 #include "libudev-private.h"
  54
  55 static int rebuild_queue_file(struct udev_queue_export *udev_queue_export);
  56
  57 struct udev_queue_export {
  58         struct udev *udev;
  59         int queued_count;        /* number of unfinished events exported in queue file */
  60         FILE *queue_file;
  61         unsigned long long int seqnum_max;        /* earliest sequence number in queue file */
  62         unsigned long long int seqnum_min;        /* latest sequence number in queue file */
  63         int waste_bytes;                        /* queue file bytes wasted on finished events */
  64 };
  65
  66 struct udev_queue_export *udev_queue_export_new(struct udev *udev)
  67 {
  68         struct udev_queue_export *udev_queue_export;
  69         unsigned long long int initial_seqnum;
  70
  71         if (udev == NULL)
  72                 return NULL;
  73
  74         udev_queue_export = calloc(1, sizeof(struct udev_queue_export));
  75         if (udev_queue_export == NULL)
  76                 return NULL;
  77         udev_queue_export->udev = udev;
  78
  79         initial_seqnum = udev_get_kernel_seqnum(udev);
  80         udev_queue_export->seqnum_min = initial_seqnum;
  81         udev_queue_export->seqnum_max = initial_seqnum;
  82
  83         udev_queue_export_cleanup(udev_queue_export);
  84         if (rebuild_queue_file(udev_queue_export) != 0) {
  85                 free(udev_queue_export);
  86                 return NULL;
  87         }
  88
  89         return udev_queue_export;
  90 }
  91
  92 struct udev_queue_export *udev_queue_export_unref(struct udev_queue_export *udev_queue_export)
  93 {
  94         if (udev_queue_export == NULL)
  95                 return NULL;
  96         if (udev_queue_export->queue_file != NULL)
  97                 fclose(udev_queue_export->queue_file);
  98         free(udev_queue_export);
  99         return NULL;
 100 }
 101
 102 void udev_queue_export_cleanup(struct udev_queue_export *udev_queue_export)
 103 {
 104         if (udev_queue_export == NULL)
 105                 return;
 106         unlink("/run/udev/queue.tmp");
 107         unlink("/run/udev/queue.bin");
 108 }
 109
 110 static int skip_to(FILE *file, long offset)
 111 {
 112         long old_offset;
 113
 114         /* fseek may drop buffered data, avoid it for small seeks */
 115         old_offset = ftell(file);
 116         if (offset > old_offset && offset - old_offset <= BUFSIZ) {
 117                 size_t skip_bytes = offset - old_offset;
 118                 char *buf = alloca(skip_bytes);
 119
 120                 if (fread(buf, skip_bytes, 1, file) != skip_bytes)
 121                         return -1;
 122         }
 123
 124         return fseek(file, offset, SEEK_SET);
 125 }
 126
 127 struct queue_devpaths {
 128         unsigned int devpaths_first;        /* index of first queued event */
 129         unsigned int devpaths_size;
 130         long devpaths[];                /* seqnum -> offset of devpath in queue file (or 0) */
 131 };
 132
 133 /*
 134  * Returns a table mapping seqnum to devpath file offset for currently queued events.
 135  * devpaths[i] represents the event with seqnum = i + udev_queue_export->seqnum_min.
 136  */
 137 static struct queue_devpaths *build_index(struct udev_queue_export *udev_queue_export)
 138 {
 139         struct queue_devpaths *devpaths;
 140         unsigned long long int range;
 141         long devpath_offset;
 142         ssize_t devpath_len;
 143         unsigned long long int seqnum;
 144         unsigned long long int n;
 145         unsigned int i;
 146
 147         /* seek to the first event in the file */
 148         rewind(udev_queue_export->queue_file);
 149         udev_queue_read_seqnum(udev_queue_export->queue_file, &seqnum);
 150
 151         /* allocate the table */
 152         range = udev_queue_export->seqnum_min - udev_queue_export->seqnum_max;
 153         if (range - 1 > INT_MAX) {
 154                 udev_err(udev_queue_export->udev, "queue file overflow\n");
 155                 return NULL;
 156         }
 157         devpaths = calloc(1, sizeof(struct queue_devpaths) + (range + 1) * sizeof(long));
 158         if (devpaths == NULL)
 159                 return NULL;
 160         devpaths->devpaths_size = range + 1;
 161
 162         /* read all records and populate the table */
 163         for (;;) {
 164                 if (udev_queue_read_seqnum(udev_queue_export->queue_file, &seqnum) < 0)
 165                         break;
 166                 n = seqnum - udev_queue_export->seqnum_max;
 167                 if (n >= devpaths->devpaths_size)
 168                         goto read_error;
 169
 170                 devpath_offset = ftell(udev_queue_export->queue_file);
 171                 devpath_len = udev_queue_skip_devpath(udev_queue_export->queue_file);
 172                 if (devpath_len < 0)
 173                         goto read_error;
 174
 175                 if (devpath_len > 0)
 176                         devpaths->devpaths[n] = devpath_offset;
 177                 else
 178                         devpaths->devpaths[n] = 0;
 179         }
 180
 181         /* find first queued event */
 182         for (i = 0; i < devpaths->devpaths_size; i++) {
 183                 if (devpaths->devpaths[i] != 0)
 184                         break;
 185         }
 186         devpaths->devpaths_first = i;
 187
 188         return devpaths;
 189
 190 read_error:
 191         udev_err(udev_queue_export->udev, "queue file corrupted\n");
 192         free(devpaths);
 193         return NULL;
 194 }
 195
 196 static int rebuild_queue_file(struct udev_queue_export *udev_queue_export)
 197 {
 198         unsigned long long int seqnum;
 199         struct queue_devpaths *devpaths = NULL;
 200         FILE *new_queue_file = NULL;
 201         unsigned int i;
 202
 203         /* read old queue file */
 204         if (udev_queue_export->queue_file != NULL) {
 205                 devpaths = build_index(udev_queue_export);
 206                 if (devpaths != NULL)
 207                         udev_queue_export->seqnum_max += devpaths->devpaths_first;
 208         }
 209         if (devpaths == NULL) {
 210                 udev_queue_export->queued_count = 0;
 211                 udev_queue_export->seqnum_max = udev_queue_export->seqnum_min;
 212         }
 213
 214         /* create new queue file */
 215         new_queue_file = fopen("/run/udev/queue.tmp", "w+e");
 216         if (new_queue_file == NULL)
 217                 goto error;
 218         seqnum = udev_queue_export->seqnum_max;
 219         fwrite(&seqnum, 1, sizeof(unsigned long long int), new_queue_file);
 220
 221         /* copy unfinished events only to the new file */
 222         if (devpaths != NULL) {
 223                 for (i = devpaths->devpaths_first; i < devpaths->devpaths_size; i++) {
 224                         char devpath[UTIL_PATH_SIZE];
 225                         int err;
 226                         unsigned short devpath_len;
 227
 228                         if (devpaths->devpaths[i] != 0)
 229                         {
 230                                 skip_to(udev_queue_export->queue_file, devpaths->devpaths[i]);
 231                                 err = udev_queue_read_devpath(udev_queue_export->queue_file, devpath, sizeof(devpath));
 232                                 devpath_len = err;
 233
 234                                 fwrite(&seqnum, sizeof(unsigned long long int), 1, new_queue_file);
 235                                 fwrite(&devpath_len, sizeof(unsigned short), 1, new_queue_file);
 236                                 fwrite(devpath, 1, devpath_len, new_queue_file);
 237                         }
 238                         seqnum++;
 239                 }
 240                 free(devpaths);
 241                 devpaths = NULL;
 242         }
 243         fflush(new_queue_file);
 244         if (ferror(new_queue_file))
 245                 goto error;
 246
 247         /* rename the new file on top of the old one */
 248         if (rename("/run/udev/queue.tmp", "/run/udev/queue.bin") != 0)
 249                 goto error;
 250
 251         if (udev_queue_export->queue_file != NULL)
 252                 fclose(udev_queue_export->queue_file);
 253         udev_queue_export->queue_file = new_queue_file;
 254         udev_queue_export->waste_bytes = 0;
 255
 256         return 0;
 257
 258 error:
 259         udev_err(udev_queue_export->udev, "failed to create queue file: %m\n");
 260         udev_queue_export_cleanup(udev_queue_export);
 261
 262         if (udev_queue_export->queue_file != NULL) {
 263                 fclose(udev_queue_export->queue_file);
 264                 udev_queue_export->queue_file = NULL;
 265         }
 266         if (new_queue_file != NULL)
 267                 fclose(new_queue_file);
 268
 269         if (devpaths != NULL)
 270                 free(devpaths);
 271         udev_queue_export->queued_count = 0;
 272         udev_queue_export->waste_bytes = 0;
 273         udev_queue_export->seqnum_max = udev_queue_export->seqnum_min;
 274
 275         return -1;
 276 }
 277
 278 static int write_queue_record(struct udev_queue_export *udev_queue_export,
 279                               unsigned long long int seqnum, const char *devpath, size_t devpath_len)
 280 {
 281         unsigned short len;
 282
 283         if (udev_queue_export->queue_file == NULL)
 284                 return -1;
 285
 286         if (fwrite(&seqnum, sizeof(unsigned long long int), 1, udev_queue_export->queue_file) != 1)
 287                 goto write_error;
 288
 289         len = (devpath_len < USHRT_MAX) ? devpath_len : USHRT_MAX;
 290         if (fwrite(&len, sizeof(unsigned short), 1, udev_queue_export->queue_file) != 1)
 291                 goto write_error;
 292         if (len > 0) {
 293                 if (fwrite(devpath, 1, len, udev_queue_export->queue_file) != len)
 294                         goto write_error;
 295         }
 296
 297         /* *must* flush output; caller may fork */
 298         if (fflush(udev_queue_export->queue_file) != 0)
 299                 goto write_error;
 300
 301         return 0;
 302
 303 write_error:
 304         /* if we failed half way through writing a record to a file,
 305            we should not try to write any further records to it. */
 306         udev_err(udev_queue_export->udev, "error writing to queue file: %m\n");
 307         fclose(udev_queue_export->queue_file);
 308         udev_queue_export->queue_file = NULL;
 309
 310         return -1;
 311 }
 312
 313 enum device_state {
 314         DEVICE_QUEUED,
 315         DEVICE_FINISHED,
 316 };
 317
 318 static inline size_t queue_record_size(size_t devpath_len)
 319 {
 320         return sizeof(unsigned long long int) + sizeof(unsigned short int) + devpath_len;
 321 }
 322
 323 static int update_queue(struct udev_queue_export *udev_queue_export,
 324                          struct udev_device *udev_device, enum device_state state)
 325 {
 326         unsigned long long int seqnum = udev_device_get_seqnum(udev_device);
 327         const char *devpath = NULL;
 328         size_t devpath_len = 0;
 329         int bytes;
 330         int err;
 331
 332         /* FINISHED records have a zero length devpath */
 333         if (state == DEVICE_QUEUED) {
 334                 devpath = udev_device_get_devpath(udev_device);
 335                 devpath_len = strlen(devpath);
 336         }
 337
 338         /* recover from an earlier failed rebuild */
 339         if (udev_queue_export->queue_file == NULL) {
 340                 if (rebuild_queue_file(udev_queue_export) != 0)
 341                         return -1;
 342         }
 343
 344         /* if we're removing the last event from the queue, that's the best time to rebuild it */
 345         if (state != DEVICE_QUEUED && udev_queue_export->queued_count == 1) {
 346                 /* we don't need to read the old queue file */
 347                 fclose(udev_queue_export->queue_file);
 348                 udev_queue_export->queue_file = NULL;
 349                 rebuild_queue_file(udev_queue_export);
 350                 return 0;
 351         }
 352
 353         /* try to rebuild the queue files before they grow larger than one page. */
 354         bytes = ftell(udev_queue_export->queue_file) + queue_record_size(devpath_len);
 355         if ((udev_queue_export->waste_bytes > bytes / 2) && bytes > 4096)
 356                 rebuild_queue_file(udev_queue_export);
 357
 358         /* don't record a finished event, if we already dropped the event in a failed rebuild */
 359         if (seqnum < udev_queue_export->seqnum_max)
 360                 return 0;
 361
 362         /* now write to the queue */
 363         if (state == DEVICE_QUEUED) {
 364                 udev_queue_export->queued_count++;
 365                 udev_queue_export->seqnum_min = seqnum;
 366         } else {
 367                 udev_queue_export->waste_bytes += queue_record_size(devpath_len) + queue_record_size(0);
 368                 udev_queue_export->queued_count--;
 369         }
 370         err = write_queue_record(udev_queue_export, seqnum, devpath, devpath_len);
 371
 372         /* try to handle ENOSPC */
 373         if (err != 0 && udev_queue_export->queued_count == 0) {
 374                 udev_queue_export_cleanup(udev_queue_export);
 375                 err = rebuild_queue_file(udev_queue_export);
 376         }
 377
 378         return err;
 379 }
 380
 381 static int update(struct udev_queue_export *udev_queue_export,
 382                   struct udev_device *udev_device, enum device_state state)
 383 {
 384         if (update_queue(udev_queue_export, udev_device, state) != 0)
 385                 return -1;
 386
 387         return 0;
 388 }
 389
 390 int udev_queue_export_device_queued(struct udev_queue_export *udev_queue_export, struct udev_device *udev_device)
 391 {
 392         return update(udev_queue_export, udev_device, DEVICE_QUEUED);
 393 }
 394
 395 int udev_queue_export_device_finished(struct udev_queue_export *udev_queue_export, struct udev_device *udev_device)
 396 {
 397         return update(udev_queue_export, udev_device, DEVICE_FINISHED);
 398 }