1 // SPDX-License-Identifier: GPL-2.0+
2 /*
3 * This file is part of UBIFS.
4 *
5 * Copyright (C) 2006-2008 Nokia Corporation.
6 *
7 * Authors: Adrian Hunter
8 * Artem Bityutskiy (Битюцкий Артём)
9 */
10
11 /*
12 * This file implements the budgeting sub-system which is responsible for UBIFS
13 * space management.
14 *
15 * Factors such as compression, wasted space at the ends of LEBs, space in other
16 * journal heads, the effect of updates on the index, and so on, make it
17 * impossible to accurately predict the amount of space needed. Consequently
18 * approximations are used.
19 */
20
21 #include "ubifs.h"
22 #ifndef __UBOOT__
23 #include <linux/writeback.h>
24 #else
25 #include <linux/err.h>
26 #endif
27 #include <linux/math64.h>
28
29 /*
30 * When pessimistic budget calculations say that there is no enough space,
31 * UBIFS starts writing back dirty inodes and pages, doing garbage collection,
32 * or committing. The below constant defines maximum number of times UBIFS
33 * repeats the operations.
34 */
35 #define MAX_MKSPC_RETRIES 3
36
37 /*
38 * The below constant defines amount of dirty pages which should be written
39 * back at when trying to shrink the liability.
40 */
41 #define NR_TO_WRITE 16
42
43 #ifndef __UBOOT__
44 /**
45 * shrink_liability - write-back some dirty pages/inodes.
46 * @c: UBIFS file-system description object
47 * @nr_to_write: how many dirty pages to write-back
48 *
49 * This function shrinks UBIFS liability by means of writing back some amount
50 * of dirty inodes and their pages.
51 *
52 * Note, this function synchronizes even VFS inodes which are locked
53 * (@i_mutex) by the caller of the budgeting function, because write-back does
54 * not touch @i_mutex.
55 */
shrink_liability(struct ubifs_info * c,int nr_to_write)56 static void shrink_liability(struct ubifs_info *c, int nr_to_write)
57 {
58 down_read(&c->vfs_sb->s_umount);
59 writeback_inodes_sb(c->vfs_sb, WB_REASON_FS_FREE_SPACE);
60 up_read(&c->vfs_sb->s_umount);
61 }
62
63 /**
64 * run_gc - run garbage collector.
65 * @c: UBIFS file-system description object
66 *
67 * This function runs garbage collector to make some more free space. Returns
68 * zero if a free LEB has been produced, %-EAGAIN if commit is required, and a
69 * negative error code in case of failure.
70 */
run_gc(struct ubifs_info * c)71 static int run_gc(struct ubifs_info *c)
72 {
73 int err, lnum;
74
75 /* Make some free space by garbage-collecting dirty space */
76 down_read(&c->commit_sem);
77 lnum = ubifs_garbage_collect(c, 1);
78 up_read(&c->commit_sem);
79 if (lnum < 0)
80 return lnum;
81
82 /* GC freed one LEB, return it to lprops */
83 dbg_budg("GC freed LEB %d", lnum);
84 err = ubifs_return_leb(c, lnum);
85 if (err)
86 return err;
87 return 0;
88 }
89
90 /**
91 * get_liability - calculate current liability.
92 * @c: UBIFS file-system description object
93 *
94 * This function calculates and returns current UBIFS liability, i.e. the
95 * amount of bytes UBIFS has "promised" to write to the media.
96 */
get_liability(struct ubifs_info * c)97 static long long get_liability(struct ubifs_info *c)
98 {
99 long long liab;
100
101 spin_lock(&c->space_lock);
102 liab = c->bi.idx_growth + c->bi.data_growth + c->bi.dd_growth;
103 spin_unlock(&c->space_lock);
104 return liab;
105 }
106
107 /**
108 * make_free_space - make more free space on the file-system.
109 * @c: UBIFS file-system description object
110 *
111 * This function is called when an operation cannot be budgeted because there
112 * is supposedly no free space. But in most cases there is some free space:
113 * o budgeting is pessimistic, so it always budgets more than it is actually
114 * needed, so shrinking the liability is one way to make free space - the
115 * cached data will take less space then it was budgeted for;
116 * o GC may turn some dark space into free space (budgeting treats dark space
117 * as not available);
118 * o commit may free some LEB, i.e., turn freeable LEBs into free LEBs.
119 *
120 * So this function tries to do the above. Returns %-EAGAIN if some free space
121 * was presumably made and the caller has to re-try budgeting the operation.
122 * Returns %-ENOSPC if it couldn't do more free space, and other negative error
123 * codes on failures.
124 */
make_free_space(struct ubifs_info * c)125 static int make_free_space(struct ubifs_info *c)
126 {
127 int err, retries = 0;
128 long long liab1, liab2;
129
130 do {
131 liab1 = get_liability(c);
132 /*
133 * We probably have some dirty pages or inodes (liability), try
134 * to write them back.
135 */
136 dbg_budg("liability %lld, run write-back", liab1);
137 shrink_liability(c, NR_TO_WRITE);
138
139 liab2 = get_liability(c);
140 if (liab2 < liab1)
141 return -EAGAIN;
142
143 dbg_budg("new liability %lld (not shrunk)", liab2);
144
145 /* Liability did not shrink again, try GC */
146 dbg_budg("Run GC");
147 err = run_gc(c);
148 if (!err)
149 return -EAGAIN;
150
151 if (err != -EAGAIN && err != -ENOSPC)
152 /* Some real error happened */
153 return err;
154
155 dbg_budg("Run commit (retries %d)", retries);
156 err = ubifs_run_commit(c);
157 if (err)
158 return err;
159 } while (retries++ < MAX_MKSPC_RETRIES);
160
161 return -ENOSPC;
162 }
163 #endif
164
165 /**
166 * ubifs_calc_min_idx_lebs - calculate amount of LEBs for the index.
167 * @c: UBIFS file-system description object
168 *
169 * This function calculates and returns the number of LEBs which should be kept
170 * for index usage.
171 */
ubifs_calc_min_idx_lebs(struct ubifs_info * c)172 int ubifs_calc_min_idx_lebs(struct ubifs_info *c)
173 {
174 int idx_lebs;
175 long long idx_size;
176
177 idx_size = c->bi.old_idx_sz + c->bi.idx_growth + c->bi.uncommitted_idx;
178 /* And make sure we have thrice the index size of space reserved */
179 idx_size += idx_size << 1;
180 /*
181 * We do not maintain 'old_idx_size' as 'old_idx_lebs'/'old_idx_bytes'
182 * pair, nor similarly the two variables for the new index size, so we
183 * have to do this costly 64-bit division on fast-path.
184 */
185 idx_lebs = div_u64(idx_size + c->idx_leb_size - 1, c->idx_leb_size);
186 /*
187 * The index head is not available for the in-the-gaps method, so add an
188 * extra LEB to compensate.
189 */
190 idx_lebs += 1;
191 if (idx_lebs < MIN_INDEX_LEBS)
192 idx_lebs = MIN_INDEX_LEBS;
193 return idx_lebs;
194 }
195
196 #ifndef __UBOOT__
197 /**
198 * ubifs_calc_available - calculate available FS space.
199 * @c: UBIFS file-system description object
200 * @min_idx_lebs: minimum number of LEBs reserved for the index
201 *
202 * This function calculates and returns amount of FS space available for use.
203 */
ubifs_calc_available(const struct ubifs_info * c,int min_idx_lebs)204 long long ubifs_calc_available(const struct ubifs_info *c, int min_idx_lebs)
205 {
206 int subtract_lebs;
207 long long available;
208
209 available = c->main_bytes - c->lst.total_used;
210
211 /*
212 * Now 'available' contains theoretically available flash space
213 * assuming there is no index, so we have to subtract the space which
214 * is reserved for the index.
215 */
216 subtract_lebs = min_idx_lebs;
217
218 /* Take into account that GC reserves one LEB for its own needs */
219 subtract_lebs += 1;
220
221 /*
222 * The GC journal head LEB is not really accessible. And since
223 * different write types go to different heads, we may count only on
224 * one head's space.
225 */
226 subtract_lebs += c->jhead_cnt - 1;
227
228 /* We also reserve one LEB for deletions, which bypass budgeting */
229 subtract_lebs += 1;
230
231 available -= (long long)subtract_lebs * c->leb_size;
232
233 /* Subtract the dead space which is not available for use */
234 available -= c->lst.total_dead;
235
236 /*
237 * Subtract dark space, which might or might not be usable - it depends
238 * on the data which we have on the media and which will be written. If
239 * this is a lot of uncompressed or not-compressible data, the dark
240 * space cannot be used.
241 */
242 available -= c->lst.total_dark;
243
244 /*
245 * However, there is more dark space. The index may be bigger than
246 * @min_idx_lebs. Those extra LEBs are assumed to be available, but
247 * their dark space is not included in total_dark, so it is subtracted
248 * here.
249 */
250 if (c->lst.idx_lebs > min_idx_lebs) {
251 subtract_lebs = c->lst.idx_lebs - min_idx_lebs;
252 available -= subtract_lebs * c->dark_wm;
253 }
254
255 /* The calculations are rough and may end up with a negative number */
256 return available > 0 ? available : 0;
257 }
258
259 /**
260 * can_use_rp - check whether the user is allowed to use reserved pool.
261 * @c: UBIFS file-system description object
262 *
263 * UBIFS has so-called "reserved pool" which is flash space reserved
264 * for the superuser and for uses whose UID/GID is recorded in UBIFS superblock.
265 * This function checks whether current user is allowed to use reserved pool.
266 * Returns %1 current user is allowed to use reserved pool and %0 otherwise.
267 */
can_use_rp(struct ubifs_info * c)268 static int can_use_rp(struct ubifs_info *c)
269 {
270 if (uid_eq(current_fsuid(), c->rp_uid) || capable(CAP_SYS_RESOURCE) ||
271 (!gid_eq(c->rp_gid, GLOBAL_ROOT_GID) && in_group_p(c->rp_gid)))
272 return 1;
273 return 0;
274 }
275
276 /**
277 * do_budget_space - reserve flash space for index and data growth.
278 * @c: UBIFS file-system description object
279 *
280 * This function makes sure UBIFS has enough free LEBs for index growth and
281 * data.
282 *
283 * When budgeting index space, UBIFS reserves thrice as many LEBs as the index
284 * would take if it was consolidated and written to the flash. This guarantees
285 * that the "in-the-gaps" commit method always succeeds and UBIFS will always
286 * be able to commit dirty index. So this function basically adds amount of
287 * budgeted index space to the size of the current index, multiplies this by 3,
288 * and makes sure this does not exceed the amount of free LEBs.
289 *
290 * Notes about @c->bi.min_idx_lebs and @c->lst.idx_lebs variables:
291 * o @c->lst.idx_lebs is the number of LEBs the index currently uses. It might
292 * be large, because UBIFS does not do any index consolidation as long as
293 * there is free space. IOW, the index may take a lot of LEBs, but the LEBs
294 * will contain a lot of dirt.
295 * o @c->bi.min_idx_lebs is the number of LEBS the index presumably takes. IOW,
296 * the index may be consolidated to take up to @c->bi.min_idx_lebs LEBs.
297 *
298 * This function returns zero in case of success, and %-ENOSPC in case of
299 * failure.
300 */
do_budget_space(struct ubifs_info * c)301 static int do_budget_space(struct ubifs_info *c)
302 {
303 long long outstanding, available;
304 int lebs, rsvd_idx_lebs, min_idx_lebs;
305
306 /* First budget index space */
307 min_idx_lebs = ubifs_calc_min_idx_lebs(c);
308
309 /* Now 'min_idx_lebs' contains number of LEBs to reserve */
310 if (min_idx_lebs > c->lst.idx_lebs)
311 rsvd_idx_lebs = min_idx_lebs - c->lst.idx_lebs;
312 else
313 rsvd_idx_lebs = 0;
314
315 /*
316 * The number of LEBs that are available to be used by the index is:
317 *
318 * @c->lst.empty_lebs + @c->freeable_cnt + @c->idx_gc_cnt -
319 * @c->lst.taken_empty_lebs
320 *
321 * @c->lst.empty_lebs are available because they are empty.
322 * @c->freeable_cnt are available because they contain only free and
323 * dirty space, @c->idx_gc_cnt are available because they are index
324 * LEBs that have been garbage collected and are awaiting the commit
325 * before they can be used. And the in-the-gaps method will grab these
326 * if it needs them. @c->lst.taken_empty_lebs are empty LEBs that have
327 * already been allocated for some purpose.
328 *
329 * Note, @c->idx_gc_cnt is included to both @c->lst.empty_lebs (because
330 * these LEBs are empty) and to @c->lst.taken_empty_lebs (because they
331 * are taken until after the commit).
332 *
333 * Note, @c->lst.taken_empty_lebs may temporarily be higher by one
334 * because of the way we serialize LEB allocations and budgeting. See a
335 * comment in 'ubifs_find_free_space()'.
336 */
337 lebs = c->lst.empty_lebs + c->freeable_cnt + c->idx_gc_cnt -
338 c->lst.taken_empty_lebs;
339 if (unlikely(rsvd_idx_lebs > lebs)) {
340 dbg_budg("out of indexing space: min_idx_lebs %d (old %d), rsvd_idx_lebs %d",
341 min_idx_lebs, c->bi.min_idx_lebs, rsvd_idx_lebs);
342 return -ENOSPC;
343 }
344
345 available = ubifs_calc_available(c, min_idx_lebs);
346 outstanding = c->bi.data_growth + c->bi.dd_growth;
347
348 if (unlikely(available < outstanding)) {
349 dbg_budg("out of data space: available %lld, outstanding %lld",
350 available, outstanding);
351 return -ENOSPC;
352 }
353
354 if (available - outstanding <= c->rp_size && !can_use_rp(c))
355 return -ENOSPC;
356
357 c->bi.min_idx_lebs = min_idx_lebs;
358 return 0;
359 }
360
361 /**
362 * calc_idx_growth - calculate approximate index growth from budgeting request.
363 * @c: UBIFS file-system description object
364 * @req: budgeting request
365 *
366 * For now we assume each new node adds one znode. But this is rather poor
367 * approximation, though.
368 */
calc_idx_growth(const struct ubifs_info * c,const struct ubifs_budget_req * req)369 static int calc_idx_growth(const struct ubifs_info *c,
370 const struct ubifs_budget_req *req)
371 {
372 int znodes;
373
374 znodes = req->new_ino + (req->new_page << UBIFS_BLOCKS_PER_PAGE_SHIFT) +
375 req->new_dent;
376 return znodes * c->max_idx_node_sz;
377 }
378
379 /**
380 * calc_data_growth - calculate approximate amount of new data from budgeting
381 * request.
382 * @c: UBIFS file-system description object
383 * @req: budgeting request
384 */
calc_data_growth(const struct ubifs_info * c,const struct ubifs_budget_req * req)385 static int calc_data_growth(const struct ubifs_info *c,
386 const struct ubifs_budget_req *req)
387 {
388 int data_growth;
389
390 data_growth = req->new_ino ? c->bi.inode_budget : 0;
391 if (req->new_page)
392 data_growth += c->bi.page_budget;
393 if (req->new_dent)
394 data_growth += c->bi.dent_budget;
395 data_growth += req->new_ino_d;
396 return data_growth;
397 }
398
399 /**
400 * calc_dd_growth - calculate approximate amount of data which makes other data
401 * dirty from budgeting request.
402 * @c: UBIFS file-system description object
403 * @req: budgeting request
404 */
calc_dd_growth(const struct ubifs_info * c,const struct ubifs_budget_req * req)405 static int calc_dd_growth(const struct ubifs_info *c,
406 const struct ubifs_budget_req *req)
407 {
408 int dd_growth;
409
410 dd_growth = req->dirtied_page ? c->bi.page_budget : 0;
411
412 if (req->dirtied_ino)
413 dd_growth += c->bi.inode_budget << (req->dirtied_ino - 1);
414 if (req->mod_dent)
415 dd_growth += c->bi.dent_budget;
416 dd_growth += req->dirtied_ino_d;
417 return dd_growth;
418 }
419
420 /**
421 * ubifs_budget_space - ensure there is enough space to complete an operation.
422 * @c: UBIFS file-system description object
423 * @req: budget request
424 *
425 * This function allocates budget for an operation. It uses pessimistic
426 * approximation of how much flash space the operation needs. The goal of this
427 * function is to make sure UBIFS always has flash space to flush all dirty
428 * pages, dirty inodes, and dirty znodes (liability). This function may force
429 * commit, garbage-collection or write-back. Returns zero in case of success,
430 * %-ENOSPC if there is no free space and other negative error codes in case of
431 * failures.
432 */
ubifs_budget_space(struct ubifs_info * c,struct ubifs_budget_req * req)433 int ubifs_budget_space(struct ubifs_info *c, struct ubifs_budget_req *req)
434 {
435 int err, idx_growth, data_growth, dd_growth, retried = 0;
436
437 ubifs_assert(req->new_page <= 1);
438 ubifs_assert(req->dirtied_page <= 1);
439 ubifs_assert(req->new_dent <= 1);
440 ubifs_assert(req->mod_dent <= 1);
441 ubifs_assert(req->new_ino <= 1);
442 ubifs_assert(req->new_ino_d <= UBIFS_MAX_INO_DATA);
443 ubifs_assert(req->dirtied_ino <= 4);
444 ubifs_assert(req->dirtied_ino_d <= UBIFS_MAX_INO_DATA * 4);
445 ubifs_assert(!(req->new_ino_d & 7));
446 ubifs_assert(!(req->dirtied_ino_d & 7));
447
448 data_growth = calc_data_growth(c, req);
449 dd_growth = calc_dd_growth(c, req);
450 if (!data_growth && !dd_growth)
451 return 0;
452 idx_growth = calc_idx_growth(c, req);
453
454 again:
455 spin_lock(&c->space_lock);
456 ubifs_assert(c->bi.idx_growth >= 0);
457 ubifs_assert(c->bi.data_growth >= 0);
458 ubifs_assert(c->bi.dd_growth >= 0);
459
460 if (unlikely(c->bi.nospace) && (c->bi.nospace_rp || !can_use_rp(c))) {
461 dbg_budg("no space");
462 spin_unlock(&c->space_lock);
463 return -ENOSPC;
464 }
465
466 c->bi.idx_growth += idx_growth;
467 c->bi.data_growth += data_growth;
468 c->bi.dd_growth += dd_growth;
469
470 err = do_budget_space(c);
471 if (likely(!err)) {
472 req->idx_growth = idx_growth;
473 req->data_growth = data_growth;
474 req->dd_growth = dd_growth;
475 spin_unlock(&c->space_lock);
476 return 0;
477 }
478
479 /* Restore the old values */
480 c->bi.idx_growth -= idx_growth;
481 c->bi.data_growth -= data_growth;
482 c->bi.dd_growth -= dd_growth;
483 spin_unlock(&c->space_lock);
484
485 if (req->fast) {
486 dbg_budg("no space for fast budgeting");
487 return err;
488 }
489
490 err = make_free_space(c);
491 cond_resched();
492 if (err == -EAGAIN) {
493 dbg_budg("try again");
494 goto again;
495 } else if (err == -ENOSPC) {
496 if (!retried) {
497 retried = 1;
498 dbg_budg("-ENOSPC, but anyway try once again");
499 goto again;
500 }
501 dbg_budg("FS is full, -ENOSPC");
502 c->bi.nospace = 1;
503 if (can_use_rp(c) || c->rp_size == 0)
504 c->bi.nospace_rp = 1;
505 smp_wmb();
506 } else
507 ubifs_err(c, "cannot budget space, error %d", err);
508 return err;
509 }
510
511 /**
512 * ubifs_release_budget - release budgeted free space.
513 * @c: UBIFS file-system description object
514 * @req: budget request
515 *
516 * This function releases the space budgeted by 'ubifs_budget_space()'. Note,
517 * since the index changes (which were budgeted for in @req->idx_growth) will
518 * only be written to the media on commit, this function moves the index budget
519 * from @c->bi.idx_growth to @c->bi.uncommitted_idx. The latter will be zeroed
520 * by the commit operation.
521 */
ubifs_release_budget(struct ubifs_info * c,struct ubifs_budget_req * req)522 void ubifs_release_budget(struct ubifs_info *c, struct ubifs_budget_req *req)
523 {
524 ubifs_assert(req->new_page <= 1);
525 ubifs_assert(req->dirtied_page <= 1);
526 ubifs_assert(req->new_dent <= 1);
527 ubifs_assert(req->mod_dent <= 1);
528 ubifs_assert(req->new_ino <= 1);
529 ubifs_assert(req->new_ino_d <= UBIFS_MAX_INO_DATA);
530 ubifs_assert(req->dirtied_ino <= 4);
531 ubifs_assert(req->dirtied_ino_d <= UBIFS_MAX_INO_DATA * 4);
532 ubifs_assert(!(req->new_ino_d & 7));
533 ubifs_assert(!(req->dirtied_ino_d & 7));
534 if (!req->recalculate) {
535 ubifs_assert(req->idx_growth >= 0);
536 ubifs_assert(req->data_growth >= 0);
537 ubifs_assert(req->dd_growth >= 0);
538 }
539
540 if (req->recalculate) {
541 req->data_growth = calc_data_growth(c, req);
542 req->dd_growth = calc_dd_growth(c, req);
543 req->idx_growth = calc_idx_growth(c, req);
544 }
545
546 if (!req->data_growth && !req->dd_growth)
547 return;
548
549 c->bi.nospace = c->bi.nospace_rp = 0;
550 smp_wmb();
551
552 spin_lock(&c->space_lock);
553 c->bi.idx_growth -= req->idx_growth;
554 c->bi.uncommitted_idx += req->idx_growth;
555 c->bi.data_growth -= req->data_growth;
556 c->bi.dd_growth -= req->dd_growth;
557 c->bi.min_idx_lebs = ubifs_calc_min_idx_lebs(c);
558
559 ubifs_assert(c->bi.idx_growth >= 0);
560 ubifs_assert(c->bi.data_growth >= 0);
561 ubifs_assert(c->bi.dd_growth >= 0);
562 ubifs_assert(c->bi.min_idx_lebs < c->main_lebs);
563 ubifs_assert(!(c->bi.idx_growth & 7));
564 ubifs_assert(!(c->bi.data_growth & 7));
565 ubifs_assert(!(c->bi.dd_growth & 7));
566 spin_unlock(&c->space_lock);
567 }
568
569 /**
570 * ubifs_convert_page_budget - convert budget of a new page.
571 * @c: UBIFS file-system description object
572 *
573 * This function converts budget which was allocated for a new page of data to
574 * the budget of changing an existing page of data. The latter is smaller than
575 * the former, so this function only does simple re-calculation and does not
576 * involve any write-back.
577 */
ubifs_convert_page_budget(struct ubifs_info * c)578 void ubifs_convert_page_budget(struct ubifs_info *c)
579 {
580 spin_lock(&c->space_lock);
581 /* Release the index growth reservation */
582 c->bi.idx_growth -= c->max_idx_node_sz << UBIFS_BLOCKS_PER_PAGE_SHIFT;
583 /* Release the data growth reservation */
584 c->bi.data_growth -= c->bi.page_budget;
585 /* Increase the dirty data growth reservation instead */
586 c->bi.dd_growth += c->bi.page_budget;
587 /* And re-calculate the indexing space reservation */
588 c->bi.min_idx_lebs = ubifs_calc_min_idx_lebs(c);
589 spin_unlock(&c->space_lock);
590 }
591
592 /**
593 * ubifs_release_dirty_inode_budget - release dirty inode budget.
594 * @c: UBIFS file-system description object
595 * @ui: UBIFS inode to release the budget for
596 *
597 * This function releases budget corresponding to a dirty inode. It is usually
598 * called when after the inode has been written to the media and marked as
599 * clean. It also causes the "no space" flags to be cleared.
600 */
ubifs_release_dirty_inode_budget(struct ubifs_info * c,struct ubifs_inode * ui)601 void ubifs_release_dirty_inode_budget(struct ubifs_info *c,
602 struct ubifs_inode *ui)
603 {
604 struct ubifs_budget_req req;
605
606 memset(&req, 0, sizeof(struct ubifs_budget_req));
607 /* The "no space" flags will be cleared because dd_growth is > 0 */
608 req.dd_growth = c->bi.inode_budget + ALIGN(ui->data_len, 8);
609 ubifs_release_budget(c, &req);
610 }
611 #endif
612
613 /**
614 * ubifs_reported_space - calculate reported free space.
615 * @c: the UBIFS file-system description object
616 * @free: amount of free space
617 *
618 * This function calculates amount of free space which will be reported to
619 * user-space. User-space application tend to expect that if the file-system
620 * (e.g., via the 'statfs()' call) reports that it has N bytes available, they
621 * are able to write a file of size N. UBIFS attaches node headers to each data
622 * node and it has to write indexing nodes as well. This introduces additional
623 * overhead, and UBIFS has to report slightly less free space to meet the above
624 * expectations.
625 *
626 * This function assumes free space is made up of uncompressed data nodes and
627 * full index nodes (one per data node, tripled because we always allow enough
628 * space to write the index thrice).
629 *
630 * Note, the calculation is pessimistic, which means that most of the time
631 * UBIFS reports less space than it actually has.
632 */
ubifs_reported_space(const struct ubifs_info * c,long long free)633 long long ubifs_reported_space(const struct ubifs_info *c, long long free)
634 {
635 int divisor, factor, f;
636
637 /*
638 * Reported space size is @free * X, where X is UBIFS block size
639 * divided by UBIFS block size + all overhead one data block
640 * introduces. The overhead is the node header + indexing overhead.
641 *
642 * Indexing overhead calculations are based on the following formula:
643 * I = N/(f - 1) + 1, where I - number of indexing nodes, N - number
644 * of data nodes, f - fanout. Because effective UBIFS fanout is twice
645 * as less than maximum fanout, we assume that each data node
646 * introduces 3 * @c->max_idx_node_sz / (@c->fanout/2 - 1) bytes.
647 * Note, the multiplier 3 is because UBIFS reserves thrice as more space
648 * for the index.
649 */
650 f = c->fanout > 3 ? c->fanout >> 1 : 2;
651 factor = UBIFS_BLOCK_SIZE;
652 divisor = UBIFS_MAX_DATA_NODE_SZ;
653 divisor += (c->max_idx_node_sz * 3) / (f - 1);
654 free *= factor;
655 return div_u64(free, divisor);
656 }
657
658 #ifndef __UBOOT__
659 /**
660 * ubifs_get_free_space_nolock - return amount of free space.
661 * @c: UBIFS file-system description object
662 *
663 * This function calculates amount of free space to report to user-space.
664 *
665 * Because UBIFS may introduce substantial overhead (the index, node headers,
666 * alignment, wastage at the end of LEBs, etc), it cannot report real amount of
667 * free flash space it has (well, because not all dirty space is reclaimable,
668 * UBIFS does not actually know the real amount). If UBIFS did so, it would
669 * bread user expectations about what free space is. Users seem to accustomed
670 * to assume that if the file-system reports N bytes of free space, they would
671 * be able to fit a file of N bytes to the FS. This almost works for
672 * traditional file-systems, because they have way less overhead than UBIFS.
673 * So, to keep users happy, UBIFS tries to take the overhead into account.
674 */
ubifs_get_free_space_nolock(struct ubifs_info * c)675 long long ubifs_get_free_space_nolock(struct ubifs_info *c)
676 {
677 int rsvd_idx_lebs, lebs;
678 long long available, outstanding, free;
679
680 ubifs_assert(c->bi.min_idx_lebs == ubifs_calc_min_idx_lebs(c));
681 outstanding = c->bi.data_growth + c->bi.dd_growth;
682 available = ubifs_calc_available(c, c->bi.min_idx_lebs);
683
684 /*
685 * When reporting free space to user-space, UBIFS guarantees that it is
686 * possible to write a file of free space size. This means that for
687 * empty LEBs we may use more precise calculations than
688 * 'ubifs_calc_available()' is using. Namely, we know that in empty
689 * LEBs we would waste only @c->leb_overhead bytes, not @c->dark_wm.
690 * Thus, amend the available space.
691 *
692 * Note, the calculations below are similar to what we have in
693 * 'do_budget_space()', so refer there for comments.
694 */
695 if (c->bi.min_idx_lebs > c->lst.idx_lebs)
696 rsvd_idx_lebs = c->bi.min_idx_lebs - c->lst.idx_lebs;
697 else
698 rsvd_idx_lebs = 0;
699 lebs = c->lst.empty_lebs + c->freeable_cnt + c->idx_gc_cnt -
700 c->lst.taken_empty_lebs;
701 lebs -= rsvd_idx_lebs;
702 available += lebs * (c->dark_wm - c->leb_overhead);
703
704 if (available > outstanding)
705 free = ubifs_reported_space(c, available - outstanding);
706 else
707 free = 0;
708 return free;
709 }
710
711 /**
712 * ubifs_get_free_space - return amount of free space.
713 * @c: UBIFS file-system description object
714 *
715 * This function calculates and returns amount of free space to report to
716 * user-space.
717 */
ubifs_get_free_space(struct ubifs_info * c)718 long long ubifs_get_free_space(struct ubifs_info *c)
719 {
720 long long free;
721
722 spin_lock(&c->space_lock);
723 free = ubifs_get_free_space_nolock(c);
724 spin_unlock(&c->space_lock);
725
726 return free;
727 }
728 #endif
729