cdf9bfe10137ff4804c49fc85a666478e9c937cd
[releases.git] / 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 }