fsmap.c

   1 // SPDX-License-Identifier: GPL-2.0+
   2 /*
   3  * Copyright (C) 2017 Oracle.  All Rights Reserved.
   4  *
   5  * Author: Darrick J. Wong <darrick.wong@oracle.com>
   6  */
   7 #include "ext4.h"
   8 #include <linux/fsmap.h>
   9 #include "fsmap.h"
  10 #include "mballoc.h"
  11 #include <linux/sort.h>
  12 #include <linux/list_sort.h>
  13 #include <trace/events/ext4.h>
  14
  15 /* Convert an ext4_fsmap to an fsmap. */
  16 void ext4_fsmap_from_internal(struct super_block *sb, struct fsmap *dest,
  17                               struct ext4_fsmap *src)
  18 {
  19         dest->fmr_device = src->fmr_device;
  20         dest->fmr_flags = src->fmr_flags;
  21         dest->fmr_physical = src->fmr_physical << sb->s_blocksize_bits;
  22         dest->fmr_owner = src->fmr_owner;
  23         dest->fmr_offset = 0;
  24         dest->fmr_length = src->fmr_length << sb->s_blocksize_bits;
  25         dest->fmr_reserved[0] = 0;
  26         dest->fmr_reserved[1] = 0;
  27         dest->fmr_reserved[2] = 0;
  28 }
  29
  30 /* Convert an fsmap to an ext4_fsmap. */
  31 void ext4_fsmap_to_internal(struct super_block *sb, struct ext4_fsmap *dest,
  32                             struct fsmap *src)
  33 {
  34         dest->fmr_device = src->fmr_device;
  35         dest->fmr_flags = src->fmr_flags;
  36         dest->fmr_physical = src->fmr_physical >> sb->s_blocksize_bits;
  37         dest->fmr_owner = src->fmr_owner;
  38         dest->fmr_length = src->fmr_length >> sb->s_blocksize_bits;
  39 }
  40
  41 /* getfsmap query state */
  42 struct ext4_getfsmap_info {
  43         struct ext4_fsmap_head  *gfi_head;
  44         ext4_fsmap_format_t     gfi_formatter;  /* formatting fn */
  45         void                    *gfi_format_arg;/* format buffer */
  46         ext4_fsblk_t            gfi_next_fsblk; /* next fsblock we expect */
  47         u32                     gfi_dev;        /* device id */
  48         ext4_group_t            gfi_agno;       /* bg number, if applicable */
  49         struct ext4_fsmap       gfi_low;        /* low rmap key */
  50         struct ext4_fsmap       gfi_high;       /* high rmap key */
  51         struct ext4_fsmap       gfi_lastfree;   /* free ext at end of last bg */
  52         struct list_head        gfi_meta_list;  /* fixed metadata list */
  53         bool                    gfi_last;       /* last extent? */
  54 };
  55
  56 /* Associate a device with a getfsmap handler. */
  57 struct ext4_getfsmap_dev {
  58         int                     (*gfd_fn)(struct super_block *sb,
  59                                       struct ext4_fsmap *keys,
  60                                       struct ext4_getfsmap_info *info);
  61         u32                     gfd_dev;
  62 };
  63
  64 /* Compare two getfsmap device handlers. */
  65 static int ext4_getfsmap_dev_compare(const void *p1, const void *p2)
  66 {
  67         const struct ext4_getfsmap_dev *d1 = p1;
  68         const struct ext4_getfsmap_dev *d2 = p2;
  69
  70         return d1->gfd_dev - d2->gfd_dev;
  71 }
  72
  73 /* Compare a record against our starting point */
  74 static bool ext4_getfsmap_rec_before_low_key(struct ext4_getfsmap_info *info,
  75                                              struct ext4_fsmap *rec)
  76 {
  77         return rec->fmr_physical < info->gfi_low.fmr_physical;
  78 }
  79
  80 /*
  81  * Format a reverse mapping for getfsmap, having translated rm_startblock
  82  * into the appropriate daddr units.
  83  */
  84 static int ext4_getfsmap_helper(struct super_block *sb,
  85                                 struct ext4_getfsmap_info *info,
  86                                 struct ext4_fsmap *rec)
  87 {
  88         struct ext4_fsmap fmr;
  89         struct ext4_sb_info *sbi = EXT4_SB(sb);
  90         ext4_fsblk_t rec_fsblk = rec->fmr_physical;
  91         ext4_group_t agno;
  92         ext4_grpblk_t cno;
  93         int error;
  94
  95         if (fatal_signal_pending(current))
  96                 return -EINTR;
  97
  98         /*
  99          * Filter out records that start before our startpoint, if the
 100          * caller requested that.
 101          */
 102         if (ext4_getfsmap_rec_before_low_key(info, rec)) {
 103                 rec_fsblk += rec->fmr_length;
 104                 if (info->gfi_next_fsblk < rec_fsblk)
 105                         info->gfi_next_fsblk = rec_fsblk;
 106                 return EXT4_QUERY_RANGE_CONTINUE;
 107         }
 108
 109         /* Are we just counting mappings? */
 110         if (info->gfi_head->fmh_count == 0) {
 111                 if (info->gfi_head->fmh_entries == UINT_MAX)
 112                         return EXT4_QUERY_RANGE_ABORT;
 113
 114                 if (rec_fsblk > info->gfi_next_fsblk)
 115                         info->gfi_head->fmh_entries++;
 116
 117                 if (info->gfi_last)
 118                         return EXT4_QUERY_RANGE_CONTINUE;
 119
 120                 info->gfi_head->fmh_entries++;
 121
 122                 rec_fsblk += rec->fmr_length;
 123                 if (info->gfi_next_fsblk < rec_fsblk)
 124                         info->gfi_next_fsblk = rec_fsblk;
 125                 return EXT4_QUERY_RANGE_CONTINUE;
 126         }
 127
 128         /*
 129          * If the record starts past the last physical block we saw,
 130          * then we've found a gap.  Report the gap as being owned by
 131          * whatever the caller specified is the missing owner.
 132          */
 133         if (rec_fsblk > info->gfi_next_fsblk) {
 134                 if (info->gfi_head->fmh_entries >= info->gfi_head->fmh_count)
 135                         return EXT4_QUERY_RANGE_ABORT;
 136
 137                 ext4_get_group_no_and_offset(sb, info->gfi_next_fsblk,
 138                                 &agno, &cno);
 139                 trace_ext4_fsmap_mapping(sb, info->gfi_dev, agno,
 140                                 EXT4_C2B(sbi, cno),
 141                                 rec_fsblk - info->gfi_next_fsblk,
 142                                 EXT4_FMR_OWN_UNKNOWN);
 143
 144                 fmr.fmr_device = info->gfi_dev;
 145                 fmr.fmr_physical = info->gfi_next_fsblk;
 146                 fmr.fmr_owner = EXT4_FMR_OWN_UNKNOWN;
 147                 fmr.fmr_length = rec_fsblk - info->gfi_next_fsblk;
 148                 fmr.fmr_flags = FMR_OF_SPECIAL_OWNER;
 149                 error = info->gfi_formatter(&fmr, info->gfi_format_arg);
 150                 if (error)
 151                         return error;
 152                 info->gfi_head->fmh_entries++;
 153         }
 154
 155         if (info->gfi_last)
 156                 goto out;
 157
 158         /* Fill out the extent we found */
 159         if (info->gfi_head->fmh_entries >= info->gfi_head->fmh_count)
 160                 return EXT4_QUERY_RANGE_ABORT;
 161
 162         ext4_get_group_no_and_offset(sb, rec_fsblk, &agno, &cno);
 163         trace_ext4_fsmap_mapping(sb, info->gfi_dev, agno, EXT4_C2B(sbi, cno),
 164                         rec->fmr_length, rec->fmr_owner);
 165
 166         fmr.fmr_device = info->gfi_dev;
 167         fmr.fmr_physical = rec_fsblk;
 168         fmr.fmr_owner = rec->fmr_owner;
 169         fmr.fmr_flags = FMR_OF_SPECIAL_OWNER;
 170         fmr.fmr_length = rec->fmr_length;
 171         error = info->gfi_formatter(&fmr, info->gfi_format_arg);
 172         if (error)
 173                 return error;
 174         info->gfi_head->fmh_entries++;
 175
 176 out:
 177         rec_fsblk += rec->fmr_length;
 178         if (info->gfi_next_fsblk < rec_fsblk)
 179                 info->gfi_next_fsblk = rec_fsblk;
 180         return EXT4_QUERY_RANGE_CONTINUE;
 181 }
 182
 183 static inline ext4_fsblk_t ext4_fsmap_next_pblk(struct ext4_fsmap *fmr)
 184 {
 185         return fmr->fmr_physical + fmr->fmr_length;
 186 }
 187
 188 /* Transform a blockgroup's free record into a fsmap */
 189 static int ext4_getfsmap_datadev_helper(struct super_block *sb,
 190                                         ext4_group_t agno, ext4_grpblk_t start,
 191                                         ext4_grpblk_t len, void *priv)
 192 {
 193         struct ext4_fsmap irec;
 194         struct ext4_getfsmap_info *info = priv;
 195         struct ext4_fsmap *p;
 196         struct ext4_fsmap *tmp;
 197         struct ext4_sb_info *sbi = EXT4_SB(sb);
 198         ext4_fsblk_t fsb;
 199         ext4_fsblk_t fslen;
 200         int error;
 201
 202         fsb = (EXT4_C2B(sbi, start) + ext4_group_first_block_no(sb, agno));
 203         fslen = EXT4_C2B(sbi, len);
 204
 205         /* If the retained free extent record is set... */
 206         if (info->gfi_lastfree.fmr_owner) {
 207                 /* ...and abuts this one, lengthen it and return. */
 208                 if (ext4_fsmap_next_pblk(&info->gfi_lastfree) == fsb) {
 209                         info->gfi_lastfree.fmr_length += fslen;
 210                         return 0;
 211                 }
 212
 213                 /*
 214                  * There's a gap between the two free extents; emit the
 215                  * retained extent prior to merging the meta_list.
 216                  */
 217                 error = ext4_getfsmap_helper(sb, info, &info->gfi_lastfree);
 218                 if (error)
 219                         return error;
 220                 info->gfi_lastfree.fmr_owner = 0;
 221         }
 222
 223         /* Merge in any relevant extents from the meta_list */
 224         list_for_each_entry_safe(p, tmp, &info->gfi_meta_list, fmr_list) {
 225                 if (p->fmr_physical + p->fmr_length <= info->gfi_next_fsblk) {
 226                         list_del(&p->fmr_list);
 227                         kfree(p);
 228                 } else if (p->fmr_physical < fsb) {
 229                         error = ext4_getfsmap_helper(sb, info, p);
 230                         if (error)
 231                                 return error;
 232
 233                         list_del(&p->fmr_list);
 234                         kfree(p);
 235                 }
 236         }
 237
 238         irec.fmr_device = 0;
 239         irec.fmr_physical = fsb;
 240         irec.fmr_length = fslen;
 241         irec.fmr_owner = EXT4_FMR_OWN_FREE;
 242         irec.fmr_flags = 0;
 243
 244         /* If this is a free extent at the end of a bg, buffer it. */
 245         if (ext4_fsmap_next_pblk(&irec) ==
 246                         ext4_group_first_block_no(sb, agno + 1)) {
 247                 info->gfi_lastfree = irec;
 248                 return 0;
 249         }
 250
 251         /* Otherwise, emit it */
 252         return ext4_getfsmap_helper(sb, info, &irec);
 253 }
 254
 255 /* Execute a getfsmap query against the log device. */
 256 static int ext4_getfsmap_logdev(struct super_block *sb, struct ext4_fsmap *keys,
 257                                 struct ext4_getfsmap_info *info)
 258 {
 259         journal_t *journal = EXT4_SB(sb)->s_journal;
 260         struct ext4_fsmap irec;
 261
 262         /* Set up search keys */
 263         info->gfi_low = keys[0];
 264         info->gfi_low.fmr_length = 0;
 265
 266         memset(&info->gfi_high, 0xFF, sizeof(info->gfi_high));
 267
 268         trace_ext4_fsmap_low_key(sb, info->gfi_dev, 0,
 269                         info->gfi_low.fmr_physical,
 270                         info->gfi_low.fmr_length,
 271                         info->gfi_low.fmr_owner);
 272
 273         trace_ext4_fsmap_high_key(sb, info->gfi_dev, 0,
 274                         info->gfi_high.fmr_physical,
 275                         info->gfi_high.fmr_length,
 276                         info->gfi_high.fmr_owner);
 277
 278         if (keys[0].fmr_physical > 0)
 279                 return 0;
 280
 281         /* Fabricate an rmap entry for the external log device. */
 282         irec.fmr_physical = journal->j_blk_offset;
 283         irec.fmr_length = journal->j_total_len;
 284         irec.fmr_owner = EXT4_FMR_OWN_LOG;
 285         irec.fmr_flags = 0;
 286
 287         return ext4_getfsmap_helper(sb, info, &irec);
 288 }
 289
 290 /* Helper to fill out an ext4_fsmap. */
 291 static inline int ext4_getfsmap_fill(struct list_head *meta_list,
 292                                      ext4_fsblk_t fsb, ext4_fsblk_t len,
 293                                      uint64_t owner)
 294 {
 295         struct ext4_fsmap *fsm;
 296
 297         fsm = kmalloc(sizeof(*fsm), GFP_NOFS);
 298         if (!fsm)
 299                 return -ENOMEM;
 300         fsm->fmr_device = 0;
 301         fsm->fmr_flags = 0;
 302         fsm->fmr_physical = fsb;
 303         fsm->fmr_owner = owner;
 304         fsm->fmr_length = len;
 305         list_add_tail(&fsm->fmr_list, meta_list);
 306
 307         return 0;
 308 }
 309
 310 /*
 311  * This function returns the number of file system metadata blocks at
 312  * the beginning of a block group, including the reserved gdt blocks.
 313  */
 314 static unsigned int ext4_getfsmap_find_sb(struct super_block *sb,
 315                                           ext4_group_t agno,
 316                                           struct list_head *meta_list)
 317 {
 318         struct ext4_sb_info *sbi = EXT4_SB(sb);
 319         ext4_fsblk_t fsb = ext4_group_first_block_no(sb, agno);
 320         ext4_fsblk_t len;
 321         unsigned long first_meta_bg = le32_to_cpu(sbi->s_es->s_first_meta_bg);
 322         unsigned long metagroup = agno / EXT4_DESC_PER_BLOCK(sb);
 323         int error;
 324
 325         /* Record the superblock. */
 326         if (ext4_bg_has_super(sb, agno)) {
 327                 error = ext4_getfsmap_fill(meta_list, fsb, 1, EXT4_FMR_OWN_FS);
 328                 if (error)
 329                         return error;
 330                 fsb++;
 331         }
 332
 333         /* Record the group descriptors. */
 334         len = ext4_bg_num_gdb(sb, agno);
 335         if (!len)
 336                 return 0;
 337         error = ext4_getfsmap_fill(meta_list, fsb, len,
 338                                    EXT4_FMR_OWN_GDT);
 339         if (error)
 340                 return error;
 341         fsb += len;
 342
 343         /* Reserved GDT blocks */
 344         if (!ext4_has_feature_meta_bg(sb) || metagroup < first_meta_bg) {
 345                 len = le16_to_cpu(sbi->s_es->s_reserved_gdt_blocks);
 346                 error = ext4_getfsmap_fill(meta_list, fsb, len,
 347                                            EXT4_FMR_OWN_RESV_GDT);
 348                 if (error)
 349                         return error;
 350         }
 351
 352         return 0;
 353 }
 354
 355 /* Compare two fsmap items. */
 356 static int ext4_getfsmap_compare(void *priv,
 357                                  const struct list_head *a,
 358                                  const struct list_head *b)
 359 {
 360         struct ext4_fsmap *fa;
 361         struct ext4_fsmap *fb;
 362
 363         fa = container_of(a, struct ext4_fsmap, fmr_list);
 364         fb = container_of(b, struct ext4_fsmap, fmr_list);
 365         if (fa->fmr_physical < fb->fmr_physical)
 366                 return -1;
 367         else if (fa->fmr_physical > fb->fmr_physical)
 368                 return 1;
 369         return 0;
 370 }
 371
 372 /* Merge adjacent extents of fixed metadata. */
 373 static void ext4_getfsmap_merge_fixed_metadata(struct list_head *meta_list)
 374 {
 375         struct ext4_fsmap *p;
 376         struct ext4_fsmap *prev = NULL;
 377         struct ext4_fsmap *tmp;
 378
 379         list_for_each_entry_safe(p, tmp, meta_list, fmr_list) {
 380                 if (!prev) {
 381                         prev = p;
 382                         continue;
 383                 }
 384
 385                 if (prev->fmr_owner == p->fmr_owner &&
 386                     prev->fmr_physical + prev->fmr_length == p->fmr_physical) {
 387                         prev->fmr_length += p->fmr_length;
 388                         list_del(&p->fmr_list);
 389                         kfree(p);
 390                 } else
 391                         prev = p;
 392         }
 393 }
 394
 395 /* Free a list of fixed metadata. */
 396 static void ext4_getfsmap_free_fixed_metadata(struct list_head *meta_list)
 397 {
 398         struct ext4_fsmap *p;
 399         struct ext4_fsmap *tmp;
 400
 401         list_for_each_entry_safe(p, tmp, meta_list, fmr_list) {
 402                 list_del(&p->fmr_list);
 403                 kfree(p);
 404         }
 405 }
 406
 407 /* Find all the fixed metadata in the filesystem. */
 408 static int ext4_getfsmap_find_fixed_metadata(struct super_block *sb,
 409                                              struct list_head *meta_list)
 410 {
 411         struct ext4_group_desc *gdp;
 412         ext4_group_t agno;
 413         int error;
 414
 415         INIT_LIST_HEAD(meta_list);
 416
 417         /* Collect everything. */
 418         for (agno = 0; agno < EXT4_SB(sb)->s_groups_count; agno++) {
 419                 gdp = ext4_get_group_desc(sb, agno, NULL);
 420                 if (!gdp) {
 421                         error = -EFSCORRUPTED;
 422                         goto err;
 423                 }
 424
 425                 /* Superblock & GDT */
 426                 error = ext4_getfsmap_find_sb(sb, agno, meta_list);
 427                 if (error)
 428                         goto err;
 429
 430                 /* Block bitmap */
 431                 error = ext4_getfsmap_fill(meta_list,
 432                                            ext4_block_bitmap(sb, gdp), 1,
 433                                            EXT4_FMR_OWN_BLKBM);
 434                 if (error)
 435                         goto err;
 436
 437                 /* Inode bitmap */
 438                 error = ext4_getfsmap_fill(meta_list,
 439                                            ext4_inode_bitmap(sb, gdp), 1,
 440                                            EXT4_FMR_OWN_INOBM);
 441                 if (error)
 442                         goto err;
 443
 444                 /* Inodes */
 445                 error = ext4_getfsmap_fill(meta_list,
 446                                            ext4_inode_table(sb, gdp),
 447                                            EXT4_SB(sb)->s_itb_per_group,
 448                                            EXT4_FMR_OWN_INODES);
 449                 if (error)
 450                         goto err;
 451         }
 452
 453         /* Sort the list */
 454         list_sort(NULL, meta_list, ext4_getfsmap_compare);
 455
 456         /* Merge adjacent extents */
 457         ext4_getfsmap_merge_fixed_metadata(meta_list);
 458
 459         return 0;
 460 err:
 461         ext4_getfsmap_free_fixed_metadata(meta_list);
 462         return error;
 463 }
 464
 465 /* Execute a getfsmap query against the buddy bitmaps */
 466 static int ext4_getfsmap_datadev(struct super_block *sb,
 467                                  struct ext4_fsmap *keys,
 468                                  struct ext4_getfsmap_info *info)
 469 {
 470         struct ext4_sb_info *sbi = EXT4_SB(sb);
 471         ext4_fsblk_t start_fsb;
 472         ext4_fsblk_t end_fsb;
 473         ext4_fsblk_t bofs;
 474         ext4_fsblk_t eofs;
 475         ext4_group_t start_ag;
 476         ext4_group_t end_ag;
 477         ext4_grpblk_t first_cluster;
 478         ext4_grpblk_t last_cluster;
 479         int error = 0;
 480
 481         bofs = le32_to_cpu(sbi->s_es->s_first_data_block);
 482         eofs = ext4_blocks_count(sbi->s_es);
 483         if (keys[0].fmr_physical >= eofs)
 484                 return 0;
 485         else if (keys[0].fmr_physical < bofs)
 486                 keys[0].fmr_physical = bofs;
 487         if (keys[1].fmr_physical >= eofs)
 488                 keys[1].fmr_physical = eofs - 1;
 489         if (keys[1].fmr_physical < keys[0].fmr_physical)
 490                 return 0;
 491         start_fsb = keys[0].fmr_physical;
 492         end_fsb = keys[1].fmr_physical;
 493
 494         /* Determine first and last group to examine based on start and end */
 495         ext4_get_group_no_and_offset(sb, start_fsb, &start_ag, &first_cluster);
 496         ext4_get_group_no_and_offset(sb, end_fsb, &end_ag, &last_cluster);
 497
 498         /*
 499          * Convert the fsmap low/high keys to bg based keys.  Initialize
 500          * low to the fsmap low key and max out the high key to the end
 501          * of the bg.
 502          */
 503         info->gfi_low = keys[0];
 504         info->gfi_low.fmr_physical = EXT4_C2B(sbi, first_cluster);
 505         info->gfi_low.fmr_length = 0;
 506
 507         memset(&info->gfi_high, 0xFF, sizeof(info->gfi_high));
 508
 509         /* Assemble a list of all the fixed-location metadata. */
 510         error = ext4_getfsmap_find_fixed_metadata(sb, &info->gfi_meta_list);
 511         if (error)
 512                 goto err;
 513
 514         /* Query each bg */
 515         for (info->gfi_agno = start_ag;
 516              info->gfi_agno <= end_ag;
 517              info->gfi_agno++) {
 518                 /*
 519                  * Set the bg high key from the fsmap high key if this
 520                  * is the last bg that we're querying.
 521                  */
 522                 if (info->gfi_agno == end_ag) {
 523                         info->gfi_high = keys[1];
 524                         info->gfi_high.fmr_physical = EXT4_C2B(sbi,
 525                                         last_cluster);
 526                         info->gfi_high.fmr_length = 0;
 527                 }
 528
 529                 trace_ext4_fsmap_low_key(sb, info->gfi_dev, info->gfi_agno,
 530                                 info->gfi_low.fmr_physical,
 531                                 info->gfi_low.fmr_length,
 532                                 info->gfi_low.fmr_owner);
 533
 534                 trace_ext4_fsmap_high_key(sb, info->gfi_dev, info->gfi_agno,
 535                                 info->gfi_high.fmr_physical,
 536                                 info->gfi_high.fmr_length,
 537                                 info->gfi_high.fmr_owner);
 538
 539                 error = ext4_mballoc_query_range(sb, info->gfi_agno,
 540                                 EXT4_B2C(sbi, info->gfi_low.fmr_physical),
 541                                 EXT4_B2C(sbi, info->gfi_high.fmr_physical),
 542                                 ext4_getfsmap_datadev_helper, info);
 543                 if (error)
 544                         goto err;
 545
 546                 /*
 547                  * Set the bg low key to the start of the bg prior to
 548                  * moving on to the next bg.
 549                  */
 550                 if (info->gfi_agno == start_ag)
 551                         memset(&info->gfi_low, 0, sizeof(info->gfi_low));
 552         }
 553
 554         /* Do we have a retained free extent? */
 555         if (info->gfi_lastfree.fmr_owner) {
 556                 error = ext4_getfsmap_helper(sb, info, &info->gfi_lastfree);
 557                 if (error)
 558                         goto err;
 559         }
 560
 561         /* Report any gaps at the end of the bg */
 562         info->gfi_last = true;
 563         error = ext4_getfsmap_datadev_helper(sb, end_ag, last_cluster, 0, info);
 564         if (error)
 565                 goto err;
 566
 567 err:
 568         ext4_getfsmap_free_fixed_metadata(&info->gfi_meta_list);
 569         return error;
 570 }
 571
 572 /* Do we recognize the device? */
 573 static bool ext4_getfsmap_is_valid_device(struct super_block *sb,
 574                                           struct ext4_fsmap *fm)
 575 {
 576         if (fm->fmr_device == 0 || fm->fmr_device == UINT_MAX ||
 577             fm->fmr_device == new_encode_dev(sb->s_bdev->bd_dev))
 578                 return true;
 579         if (EXT4_SB(sb)->s_journal_bdev &&
 580             fm->fmr_device == new_encode_dev(EXT4_SB(sb)->s_journal_bdev->bd_dev))
 581                 return true;
 582         return false;
 583 }
 584
 585 /* Ensure that the low key is less than the high key. */
 586 static bool ext4_getfsmap_check_keys(struct ext4_fsmap *low_key,
 587                                      struct ext4_fsmap *high_key)
 588 {
 589         if (low_key->fmr_device > high_key->fmr_device)
 590                 return false;
 591         if (low_key->fmr_device < high_key->fmr_device)
 592                 return true;
 593
 594         if (low_key->fmr_physical > high_key->fmr_physical)
 595                 return false;
 596         if (low_key->fmr_physical < high_key->fmr_physical)
 597                 return true;
 598
 599         if (low_key->fmr_owner > high_key->fmr_owner)
 600                 return false;
 601         if (low_key->fmr_owner < high_key->fmr_owner)
 602                 return true;
 603
 604         return false;
 605 }
 606
 607 #define EXT4_GETFSMAP_DEVS      2
 608 /*
 609  * Get filesystem's extents as described in head, and format for
 610  * output.  Calls formatter to fill the user's buffer until all
 611  * extents are mapped, until the passed-in head->fmh_count slots have
 612  * been filled, or until the formatter short-circuits the loop, if it
 613  * is tracking filled-in extents on its own.
 614  *
 615  * Key to Confusion
 616  * ----------------
 617  * There are multiple levels of keys and counters at work here:
 618  * _fsmap_head.fmh_keys         -- low and high fsmap keys passed in;
 619  *                                 these reflect fs-wide block addrs.
 620  * dkeys                        -- fmh_keys used to query each device;
 621  *                                 these are fmh_keys but w/ the low key
 622  *                                 bumped up by fmr_length.
 623  * _getfsmap_info.gfi_next_fsblk-- next fs block we expect to see; this
 624  *                                 is how we detect gaps in the fsmap
 625  *                                 records and report them.
 626  * _getfsmap_info.gfi_low/high  -- per-bg low/high keys computed from
 627  *                                 dkeys; used to query the free space.
 628  */
 629 int ext4_getfsmap(struct super_block *sb, struct ext4_fsmap_head *head,
 630                   ext4_fsmap_format_t formatter, void *arg)
 631 {
 632         struct ext4_fsmap dkeys[2];     /* per-dev keys */
 633         struct ext4_getfsmap_dev handlers[EXT4_GETFSMAP_DEVS];
 634         struct ext4_getfsmap_info info = { NULL };
 635         int i;
 636         int error = 0;
 637
 638         if (head->fmh_iflags & ~FMH_IF_VALID)
 639                 return -EINVAL;
 640         if (!ext4_getfsmap_is_valid_device(sb, &head->fmh_keys[0]) ||
 641             !ext4_getfsmap_is_valid_device(sb, &head->fmh_keys[1]))
 642                 return -EINVAL;
 643
 644         head->fmh_entries = 0;
 645
 646         /* Set up our device handlers. */
 647         memset(handlers, 0, sizeof(handlers));
 648         handlers[0].gfd_dev = new_encode_dev(sb->s_bdev->bd_dev);
 649         handlers[0].gfd_fn = ext4_getfsmap_datadev;
 650         if (EXT4_SB(sb)->s_journal_bdev) {
 651                 handlers[1].gfd_dev = new_encode_dev(
 652                                 EXT4_SB(sb)->s_journal_bdev->bd_dev);
 653                 handlers[1].gfd_fn = ext4_getfsmap_logdev;
 654         }
 655
 656         sort(handlers, EXT4_GETFSMAP_DEVS, sizeof(struct ext4_getfsmap_dev),
 657                         ext4_getfsmap_dev_compare, NULL);
 658
 659         /*
 660          * To continue where we left off, we allow userspace to use the
 661          * last mapping from a previous call as the low key of the next.
 662          * This is identified by a non-zero length in the low key. We
 663          * have to increment the low key in this scenario to ensure we
 664          * don't return the same mapping again, and instead return the
 665          * very next mapping.
 666          *
 667          * Bump the physical offset as there can be no other mapping for
 668          * the same physical block range.
 669          */
 670         dkeys[0] = head->fmh_keys[0];
 671         dkeys[0].fmr_physical += dkeys[0].fmr_length;
 672         dkeys[0].fmr_owner = 0;
 673         dkeys[0].fmr_length = 0;
 674         memset(&dkeys[1], 0xFF, sizeof(struct ext4_fsmap));
 675
 676         if (!ext4_getfsmap_check_keys(dkeys, &head->fmh_keys[1]))
 677                 return -EINVAL;
 678
 679         info.gfi_next_fsblk = head->fmh_keys[0].fmr_physical +
 680                           head->fmh_keys[0].fmr_length;
 681         info.gfi_formatter = formatter;
 682         info.gfi_format_arg = arg;
 683         info.gfi_head = head;
 684
 685         /* For each device we support... */
 686         for (i = 0; i < EXT4_GETFSMAP_DEVS; i++) {
 687                 /* Is this device within the range the user asked for? */
 688                 if (!handlers[i].gfd_fn)
 689                         continue;
 690                 if (head->fmh_keys[0].fmr_device > handlers[i].gfd_dev)
 691                         continue;
 692                 if (head->fmh_keys[1].fmr_device < handlers[i].gfd_dev)
 693                         break;
 694
 695                 /*
 696                  * If this device number matches the high key, we have
 697                  * to pass the high key to the handler to limit the
 698                  * query results.  If the device number exceeds the
 699                  * low key, zero out the low key so that we get
 700                  * everything from the beginning.
 701                  */
 702                 if (handlers[i].gfd_dev == head->fmh_keys[1].fmr_device)
 703                         dkeys[1] = head->fmh_keys[1];
 704                 if (handlers[i].gfd_dev > head->fmh_keys[0].fmr_device)
 705                         memset(&dkeys[0], 0, sizeof(struct ext4_fsmap));
 706
 707                 info.gfi_dev = handlers[i].gfd_dev;
 708                 info.gfi_last = false;
 709                 info.gfi_agno = -1;
 710                 error = handlers[i].gfd_fn(sb, dkeys, &info);
 711                 if (error)
 712                         break;
 713                 info.gfi_next_fsblk = 0;
 714         }
 715
 716         head->fmh_oflags = FMH_OF_DEV_T;
 717         return error;
 718 }