xref: /openbmc/u-boot/fs/ubifs/budget.c (revision 7fb46430)
1 /*
2  * This file is part of UBIFS.
3  *
4  * Copyright (C) 2006-2008 Nokia Corporation.
5  *
6  * SPDX-License-Identifier:	GPL-2.0+
7  *
8  * Authors: Adrian Hunter
9  *          Artem Bityutskiy (Битюцкий Артём)
10  */
11 
12 /*
13  * This file implements the budgeting sub-system which is responsible for UBIFS
14  * space management.
15  *
16  * Factors such as compression, wasted space at the ends of LEBs, space in other
17  * journal heads, the effect of updates on the index, and so on, make it
18  * impossible to accurately predict the amount of space needed. Consequently
19  * approximations are used.
20  */
21 
22 #include "ubifs.h"
23 #ifndef __UBOOT__
24 #include <linux/writeback.h>
25 #else
26 #include <linux/err.h>
27 #endif
28 #include <linux/math64.h>
29 
30 /*
31  * When pessimistic budget calculations say that there is no enough space,
32  * UBIFS starts writing back dirty inodes and pages, doing garbage collection,
33  * or committing. The below constant defines maximum number of times UBIFS
34  * repeats the operations.
35  */
36 #define MAX_MKSPC_RETRIES 3
37 
38 /*
39  * The below constant defines amount of dirty pages which should be written
40  * back at when trying to shrink the liability.
41  */
42 #define NR_TO_WRITE 16
43 
44 #ifndef __UBOOT__
45 /**
46  * shrink_liability - write-back some dirty pages/inodes.
47  * @c: UBIFS file-system description object
48  * @nr_to_write: how many dirty pages to write-back
49  *
50  * This function shrinks UBIFS liability by means of writing back some amount
51  * of dirty inodes and their pages.
52  *
53  * Note, this function synchronizes even VFS inodes which are locked
54  * (@i_mutex) by the caller of the budgeting function, because write-back does
55  * not touch @i_mutex.
56  */
57 static void shrink_liability(struct ubifs_info *c, int nr_to_write)
58 {
59 	down_read(&c->vfs_sb->s_umount);
60 	writeback_inodes_sb(c->vfs_sb, WB_REASON_FS_FREE_SPACE);
61 	up_read(&c->vfs_sb->s_umount);
62 }
63 
64 /**
65  * run_gc - run garbage collector.
66  * @c: UBIFS file-system description object
67  *
68  * This function runs garbage collector to make some more free space. Returns
69  * zero if a free LEB has been produced, %-EAGAIN if commit is required, and a
70  * negative error code in case of failure.
71  */
72 static int run_gc(struct ubifs_info *c)
73 {
74 	int err, lnum;
75 
76 	/* Make some free space by garbage-collecting dirty space */
77 	down_read(&c->commit_sem);
78 	lnum = ubifs_garbage_collect(c, 1);
79 	up_read(&c->commit_sem);
80 	if (lnum < 0)
81 		return lnum;
82 
83 	/* GC freed one LEB, return it to lprops */
84 	dbg_budg("GC freed LEB %d", lnum);
85 	err = ubifs_return_leb(c, lnum);
86 	if (err)
87 		return err;
88 	return 0;
89 }
90 
91 /**
92  * get_liability - calculate current liability.
93  * @c: UBIFS file-system description object
94  *
95  * This function calculates and returns current UBIFS liability, i.e. the
96  * amount of bytes UBIFS has "promised" to write to the media.
97  */
98 static long long get_liability(struct ubifs_info *c)
99 {
100 	long long liab;
101 
102 	spin_lock(&c->space_lock);
103 	liab = c->bi.idx_growth + c->bi.data_growth + c->bi.dd_growth;
104 	spin_unlock(&c->space_lock);
105 	return liab;
106 }
107 
108 /**
109  * make_free_space - make more free space on the file-system.
110  * @c: UBIFS file-system description object
111  *
112  * This function is called when an operation cannot be budgeted because there
113  * is supposedly no free space. But in most cases there is some free space:
114  *   o budgeting is pessimistic, so it always budgets more than it is actually
115  *     needed, so shrinking the liability is one way to make free space - the
116  *     cached data will take less space then it was budgeted for;
117  *   o GC may turn some dark space into free space (budgeting treats dark space
118  *     as not available);
119  *   o commit may free some LEB, i.e., turn freeable LEBs into free LEBs.
120  *
121  * So this function tries to do the above. Returns %-EAGAIN if some free space
122  * was presumably made and the caller has to re-try budgeting the operation.
123  * Returns %-ENOSPC if it couldn't do more free space, and other negative error
124  * codes on failures.
125  */
126 static int make_free_space(struct ubifs_info *c)
127 {
128 	int err, retries = 0;
129 	long long liab1, liab2;
130 
131 	do {
132 		liab1 = get_liability(c);
133 		/*
134 		 * We probably have some dirty pages or inodes (liability), try
135 		 * to write them back.
136 		 */
137 		dbg_budg("liability %lld, run write-back", liab1);
138 		shrink_liability(c, NR_TO_WRITE);
139 
140 		liab2 = get_liability(c);
141 		if (liab2 < liab1)
142 			return -EAGAIN;
143 
144 		dbg_budg("new liability %lld (not shrunk)", liab2);
145 
146 		/* Liability did not shrink again, try GC */
147 		dbg_budg("Run GC");
148 		err = run_gc(c);
149 		if (!err)
150 			return -EAGAIN;
151 
152 		if (err != -EAGAIN && err != -ENOSPC)
153 			/* Some real error happened */
154 			return err;
155 
156 		dbg_budg("Run commit (retries %d)", retries);
157 		err = ubifs_run_commit(c);
158 		if (err)
159 			return err;
160 	} while (retries++ < MAX_MKSPC_RETRIES);
161 
162 	return -ENOSPC;
163 }
164 #endif
165 
166 /**
167  * ubifs_calc_min_idx_lebs - calculate amount of LEBs for the index.
168  * @c: UBIFS file-system description object
169  *
170  * This function calculates and returns the number of LEBs which should be kept
171  * for index usage.
172  */
173 int ubifs_calc_min_idx_lebs(struct ubifs_info *c)
174 {
175 	int idx_lebs;
176 	long long idx_size;
177 
178 	idx_size = c->bi.old_idx_sz + c->bi.idx_growth + c->bi.uncommitted_idx;
179 	/* And make sure we have thrice the index size of space reserved */
180 	idx_size += idx_size << 1;
181 	/*
182 	 * We do not maintain 'old_idx_size' as 'old_idx_lebs'/'old_idx_bytes'
183 	 * pair, nor similarly the two variables for the new index size, so we
184 	 * have to do this costly 64-bit division on fast-path.
185 	 */
186 	idx_lebs = div_u64(idx_size + c->idx_leb_size - 1, c->idx_leb_size);
187 	/*
188 	 * The index head is not available for the in-the-gaps method, so add an
189 	 * extra LEB to compensate.
190 	 */
191 	idx_lebs += 1;
192 	if (idx_lebs < MIN_INDEX_LEBS)
193 		idx_lebs = MIN_INDEX_LEBS;
194 	return idx_lebs;
195 }
196 
197 #ifndef __UBOOT__
198 /**
199  * ubifs_calc_available - calculate available FS space.
200  * @c: UBIFS file-system description object
201  * @min_idx_lebs: minimum number of LEBs reserved for the index
202  *
203  * This function calculates and returns amount of FS space available for use.
204  */
205 long long ubifs_calc_available(const struct ubifs_info *c, int min_idx_lebs)
206 {
207 	int subtract_lebs;
208 	long long available;
209 
210 	available = c->main_bytes - c->lst.total_used;
211 
212 	/*
213 	 * Now 'available' contains theoretically available flash space
214 	 * assuming there is no index, so we have to subtract the space which
215 	 * is reserved for the index.
216 	 */
217 	subtract_lebs = min_idx_lebs;
218 
219 	/* Take into account that GC reserves one LEB for its own needs */
220 	subtract_lebs += 1;
221 
222 	/*
223 	 * The GC journal head LEB is not really accessible. And since
224 	 * different write types go to different heads, we may count only on
225 	 * one head's space.
226 	 */
227 	subtract_lebs += c->jhead_cnt - 1;
228 
229 	/* We also reserve one LEB for deletions, which bypass budgeting */
230 	subtract_lebs += 1;
231 
232 	available -= (long long)subtract_lebs * c->leb_size;
233 
234 	/* Subtract the dead space which is not available for use */
235 	available -= c->lst.total_dead;
236 
237 	/*
238 	 * Subtract dark space, which might or might not be usable - it depends
239 	 * on the data which we have on the media and which will be written. If
240 	 * this is a lot of uncompressed or not-compressible data, the dark
241 	 * space cannot be used.
242 	 */
243 	available -= c->lst.total_dark;
244 
245 	/*
246 	 * However, there is more dark space. The index may be bigger than
247 	 * @min_idx_lebs. Those extra LEBs are assumed to be available, but
248 	 * their dark space is not included in total_dark, so it is subtracted
249 	 * here.
250 	 */
251 	if (c->lst.idx_lebs > min_idx_lebs) {
252 		subtract_lebs = c->lst.idx_lebs - min_idx_lebs;
253 		available -= subtract_lebs * c->dark_wm;
254 	}
255 
256 	/* The calculations are rough and may end up with a negative number */
257 	return available > 0 ? available : 0;
258 }
259 
260 /**
261  * can_use_rp - check whether the user is allowed to use reserved pool.
262  * @c: UBIFS file-system description object
263  *
264  * UBIFS has so-called "reserved pool" which is flash space reserved
265  * for the superuser and for uses whose UID/GID is recorded in UBIFS superblock.
266  * This function checks whether current user is allowed to use reserved pool.
267  * Returns %1  current user is allowed to use reserved pool and %0 otherwise.
268  */
269 static int can_use_rp(struct ubifs_info *c)
270 {
271 	if (uid_eq(current_fsuid(), c->rp_uid) || capable(CAP_SYS_RESOURCE) ||
272 	    (!gid_eq(c->rp_gid, GLOBAL_ROOT_GID) && in_group_p(c->rp_gid)))
273 		return 1;
274 	return 0;
275 }
276 
277 /**
278  * do_budget_space - reserve flash space for index and data growth.
279  * @c: UBIFS file-system description object
280  *
281  * This function makes sure UBIFS has enough free LEBs for index growth and
282  * data.
283  *
284  * When budgeting index space, UBIFS reserves thrice as many LEBs as the index
285  * would take if it was consolidated and written to the flash. This guarantees
286  * that the "in-the-gaps" commit method always succeeds and UBIFS will always
287  * be able to commit dirty index. So this function basically adds amount of
288  * budgeted index space to the size of the current index, multiplies this by 3,
289  * and makes sure this does not exceed the amount of free LEBs.
290  *
291  * Notes about @c->bi.min_idx_lebs and @c->lst.idx_lebs variables:
292  * o @c->lst.idx_lebs is the number of LEBs the index currently uses. It might
293  *    be large, because UBIFS does not do any index consolidation as long as
294  *    there is free space. IOW, the index may take a lot of LEBs, but the LEBs
295  *    will contain a lot of dirt.
296  * o @c->bi.min_idx_lebs is the number of LEBS the index presumably takes. IOW,
297  *    the index may be consolidated to take up to @c->bi.min_idx_lebs LEBs.
298  *
299  * This function returns zero in case of success, and %-ENOSPC in case of
300  * failure.
301  */
302 static int do_budget_space(struct ubifs_info *c)
303 {
304 	long long outstanding, available;
305 	int lebs, rsvd_idx_lebs, min_idx_lebs;
306 
307 	/* First budget index space */
308 	min_idx_lebs = ubifs_calc_min_idx_lebs(c);
309 
310 	/* Now 'min_idx_lebs' contains number of LEBs to reserve */
311 	if (min_idx_lebs > c->lst.idx_lebs)
312 		rsvd_idx_lebs = min_idx_lebs - c->lst.idx_lebs;
313 	else
314 		rsvd_idx_lebs = 0;
315 
316 	/*
317 	 * The number of LEBs that are available to be used by the index is:
318 	 *
319 	 *    @c->lst.empty_lebs + @c->freeable_cnt + @c->idx_gc_cnt -
320 	 *    @c->lst.taken_empty_lebs
321 	 *
322 	 * @c->lst.empty_lebs are available because they are empty.
323 	 * @c->freeable_cnt are available because they contain only free and
324 	 * dirty space, @c->idx_gc_cnt are available because they are index
325 	 * LEBs that have been garbage collected and are awaiting the commit
326 	 * before they can be used. And the in-the-gaps method will grab these
327 	 * if it needs them. @c->lst.taken_empty_lebs are empty LEBs that have
328 	 * already been allocated for some purpose.
329 	 *
330 	 * Note, @c->idx_gc_cnt is included to both @c->lst.empty_lebs (because
331 	 * these LEBs are empty) and to @c->lst.taken_empty_lebs (because they
332 	 * are taken until after the commit).
333 	 *
334 	 * Note, @c->lst.taken_empty_lebs may temporarily be higher by one
335 	 * because of the way we serialize LEB allocations and budgeting. See a
336 	 * comment in 'ubifs_find_free_space()'.
337 	 */
338 	lebs = c->lst.empty_lebs + c->freeable_cnt + c->idx_gc_cnt -
339 	       c->lst.taken_empty_lebs;
340 	if (unlikely(rsvd_idx_lebs > lebs)) {
341 		dbg_budg("out of indexing space: min_idx_lebs %d (old %d), rsvd_idx_lebs %d",
342 			 min_idx_lebs, c->bi.min_idx_lebs, rsvd_idx_lebs);
343 		return -ENOSPC;
344 	}
345 
346 	available = ubifs_calc_available(c, min_idx_lebs);
347 	outstanding = c->bi.data_growth + c->bi.dd_growth;
348 
349 	if (unlikely(available < outstanding)) {
350 		dbg_budg("out of data space: available %lld, outstanding %lld",
351 			 available, outstanding);
352 		return -ENOSPC;
353 	}
354 
355 	if (available - outstanding <= c->rp_size && !can_use_rp(c))
356 		return -ENOSPC;
357 
358 	c->bi.min_idx_lebs = min_idx_lebs;
359 	return 0;
360 }
361 
362 /**
363  * calc_idx_growth - calculate approximate index growth from budgeting request.
364  * @c: UBIFS file-system description object
365  * @req: budgeting request
366  *
367  * For now we assume each new node adds one znode. But this is rather poor
368  * approximation, though.
369  */
370 static int calc_idx_growth(const struct ubifs_info *c,
371 			   const struct ubifs_budget_req *req)
372 {
373 	int znodes;
374 
375 	znodes = req->new_ino + (req->new_page << UBIFS_BLOCKS_PER_PAGE_SHIFT) +
376 		 req->new_dent;
377 	return znodes * c->max_idx_node_sz;
378 }
379 
380 /**
381  * calc_data_growth - calculate approximate amount of new data from budgeting
382  * request.
383  * @c: UBIFS file-system description object
384  * @req: budgeting request
385  */
386 static int calc_data_growth(const struct ubifs_info *c,
387 			    const struct ubifs_budget_req *req)
388 {
389 	int data_growth;
390 
391 	data_growth = req->new_ino  ? c->bi.inode_budget : 0;
392 	if (req->new_page)
393 		data_growth += c->bi.page_budget;
394 	if (req->new_dent)
395 		data_growth += c->bi.dent_budget;
396 	data_growth += req->new_ino_d;
397 	return data_growth;
398 }
399 
400 /**
401  * calc_dd_growth - calculate approximate amount of data which makes other data
402  * dirty from budgeting request.
403  * @c: UBIFS file-system description object
404  * @req: budgeting request
405  */
406 static int calc_dd_growth(const struct ubifs_info *c,
407 			  const struct ubifs_budget_req *req)
408 {
409 	int dd_growth;
410 
411 	dd_growth = req->dirtied_page ? c->bi.page_budget : 0;
412 
413 	if (req->dirtied_ino)
414 		dd_growth += c->bi.inode_budget << (req->dirtied_ino - 1);
415 	if (req->mod_dent)
416 		dd_growth += c->bi.dent_budget;
417 	dd_growth += req->dirtied_ino_d;
418 	return dd_growth;
419 }
420 
421 /**
422  * ubifs_budget_space - ensure there is enough space to complete an operation.
423  * @c: UBIFS file-system description object
424  * @req: budget request
425  *
426  * This function allocates budget for an operation. It uses pessimistic
427  * approximation of how much flash space the operation needs. The goal of this
428  * function is to make sure UBIFS always has flash space to flush all dirty
429  * pages, dirty inodes, and dirty znodes (liability). This function may force
430  * commit, garbage-collection or write-back. Returns zero in case of success,
431  * %-ENOSPC if there is no free space and other negative error codes in case of
432  * failures.
433  */
434 int ubifs_budget_space(struct ubifs_info *c, struct ubifs_budget_req *req)
435 {
436 	int err, idx_growth, data_growth, dd_growth, retried = 0;
437 
438 	ubifs_assert(req->new_page <= 1);
439 	ubifs_assert(req->dirtied_page <= 1);
440 	ubifs_assert(req->new_dent <= 1);
441 	ubifs_assert(req->mod_dent <= 1);
442 	ubifs_assert(req->new_ino <= 1);
443 	ubifs_assert(req->new_ino_d <= UBIFS_MAX_INO_DATA);
444 	ubifs_assert(req->dirtied_ino <= 4);
445 	ubifs_assert(req->dirtied_ino_d <= UBIFS_MAX_INO_DATA * 4);
446 	ubifs_assert(!(req->new_ino_d & 7));
447 	ubifs_assert(!(req->dirtied_ino_d & 7));
448 
449 	data_growth = calc_data_growth(c, req);
450 	dd_growth = calc_dd_growth(c, req);
451 	if (!data_growth && !dd_growth)
452 		return 0;
453 	idx_growth = calc_idx_growth(c, req);
454 
455 again:
456 	spin_lock(&c->space_lock);
457 	ubifs_assert(c->bi.idx_growth >= 0);
458 	ubifs_assert(c->bi.data_growth >= 0);
459 	ubifs_assert(c->bi.dd_growth >= 0);
460 
461 	if (unlikely(c->bi.nospace) && (c->bi.nospace_rp || !can_use_rp(c))) {
462 		dbg_budg("no space");
463 		spin_unlock(&c->space_lock);
464 		return -ENOSPC;
465 	}
466 
467 	c->bi.idx_growth += idx_growth;
468 	c->bi.data_growth += data_growth;
469 	c->bi.dd_growth += dd_growth;
470 
471 	err = do_budget_space(c);
472 	if (likely(!err)) {
473 		req->idx_growth = idx_growth;
474 		req->data_growth = data_growth;
475 		req->dd_growth = dd_growth;
476 		spin_unlock(&c->space_lock);
477 		return 0;
478 	}
479 
480 	/* Restore the old values */
481 	c->bi.idx_growth -= idx_growth;
482 	c->bi.data_growth -= data_growth;
483 	c->bi.dd_growth -= dd_growth;
484 	spin_unlock(&c->space_lock);
485 
486 	if (req->fast) {
487 		dbg_budg("no space for fast budgeting");
488 		return err;
489 	}
490 
491 	err = make_free_space(c);
492 	cond_resched();
493 	if (err == -EAGAIN) {
494 		dbg_budg("try again");
495 		goto again;
496 	} else if (err == -ENOSPC) {
497 		if (!retried) {
498 			retried = 1;
499 			dbg_budg("-ENOSPC, but anyway try once again");
500 			goto again;
501 		}
502 		dbg_budg("FS is full, -ENOSPC");
503 		c->bi.nospace = 1;
504 		if (can_use_rp(c) || c->rp_size == 0)
505 			c->bi.nospace_rp = 1;
506 		smp_wmb();
507 	} else
508 		ubifs_err(c, "cannot budget space, error %d", err);
509 	return err;
510 }
511 
512 /**
513  * ubifs_release_budget - release budgeted free space.
514  * @c: UBIFS file-system description object
515  * @req: budget request
516  *
517  * This function releases the space budgeted by 'ubifs_budget_space()'. Note,
518  * since the index changes (which were budgeted for in @req->idx_growth) will
519  * only be written to the media on commit, this function moves the index budget
520  * from @c->bi.idx_growth to @c->bi.uncommitted_idx. The latter will be zeroed
521  * by the commit operation.
522  */
523 void ubifs_release_budget(struct ubifs_info *c, struct ubifs_budget_req *req)
524 {
525 	ubifs_assert(req->new_page <= 1);
526 	ubifs_assert(req->dirtied_page <= 1);
527 	ubifs_assert(req->new_dent <= 1);
528 	ubifs_assert(req->mod_dent <= 1);
529 	ubifs_assert(req->new_ino <= 1);
530 	ubifs_assert(req->new_ino_d <= UBIFS_MAX_INO_DATA);
531 	ubifs_assert(req->dirtied_ino <= 4);
532 	ubifs_assert(req->dirtied_ino_d <= UBIFS_MAX_INO_DATA * 4);
533 	ubifs_assert(!(req->new_ino_d & 7));
534 	ubifs_assert(!(req->dirtied_ino_d & 7));
535 	if (!req->recalculate) {
536 		ubifs_assert(req->idx_growth >= 0);
537 		ubifs_assert(req->data_growth >= 0);
538 		ubifs_assert(req->dd_growth >= 0);
539 	}
540 
541 	if (req->recalculate) {
542 		req->data_growth = calc_data_growth(c, req);
543 		req->dd_growth = calc_dd_growth(c, req);
544 		req->idx_growth = calc_idx_growth(c, req);
545 	}
546 
547 	if (!req->data_growth && !req->dd_growth)
548 		return;
549 
550 	c->bi.nospace = c->bi.nospace_rp = 0;
551 	smp_wmb();
552 
553 	spin_lock(&c->space_lock);
554 	c->bi.idx_growth -= req->idx_growth;
555 	c->bi.uncommitted_idx += req->idx_growth;
556 	c->bi.data_growth -= req->data_growth;
557 	c->bi.dd_growth -= req->dd_growth;
558 	c->bi.min_idx_lebs = ubifs_calc_min_idx_lebs(c);
559 
560 	ubifs_assert(c->bi.idx_growth >= 0);
561 	ubifs_assert(c->bi.data_growth >= 0);
562 	ubifs_assert(c->bi.dd_growth >= 0);
563 	ubifs_assert(c->bi.min_idx_lebs < c->main_lebs);
564 	ubifs_assert(!(c->bi.idx_growth & 7));
565 	ubifs_assert(!(c->bi.data_growth & 7));
566 	ubifs_assert(!(c->bi.dd_growth & 7));
567 	spin_unlock(&c->space_lock);
568 }
569 
570 /**
571  * ubifs_convert_page_budget - convert budget of a new page.
572  * @c: UBIFS file-system description object
573  *
574  * This function converts budget which was allocated for a new page of data to
575  * the budget of changing an existing page of data. The latter is smaller than
576  * the former, so this function only does simple re-calculation and does not
577  * involve any write-back.
578  */
579 void ubifs_convert_page_budget(struct ubifs_info *c)
580 {
581 	spin_lock(&c->space_lock);
582 	/* Release the index growth reservation */
583 	c->bi.idx_growth -= c->max_idx_node_sz << UBIFS_BLOCKS_PER_PAGE_SHIFT;
584 	/* Release the data growth reservation */
585 	c->bi.data_growth -= c->bi.page_budget;
586 	/* Increase the dirty data growth reservation instead */
587 	c->bi.dd_growth += c->bi.page_budget;
588 	/* And re-calculate the indexing space reservation */
589 	c->bi.min_idx_lebs = ubifs_calc_min_idx_lebs(c);
590 	spin_unlock(&c->space_lock);
591 }
592 
593 /**
594  * ubifs_release_dirty_inode_budget - release dirty inode budget.
595  * @c: UBIFS file-system description object
596  * @ui: UBIFS inode to release the budget for
597  *
598  * This function releases budget corresponding to a dirty inode. It is usually
599  * called when after the inode has been written to the media and marked as
600  * clean. It also causes the "no space" flags to be cleared.
601  */
602 void ubifs_release_dirty_inode_budget(struct ubifs_info *c,
603 				      struct ubifs_inode *ui)
604 {
605 	struct ubifs_budget_req req;
606 
607 	memset(&req, 0, sizeof(struct ubifs_budget_req));
608 	/* The "no space" flags will be cleared because dd_growth is > 0 */
609 	req.dd_growth = c->bi.inode_budget + ALIGN(ui->data_len, 8);
610 	ubifs_release_budget(c, &req);
611 }
612 #endif
613 
614 /**
615  * ubifs_reported_space - calculate reported free space.
616  * @c: the UBIFS file-system description object
617  * @free: amount of free space
618  *
619  * This function calculates amount of free space which will be reported to
620  * user-space. User-space application tend to expect that if the file-system
621  * (e.g., via the 'statfs()' call) reports that it has N bytes available, they
622  * are able to write a file of size N. UBIFS attaches node headers to each data
623  * node and it has to write indexing nodes as well. This introduces additional
624  * overhead, and UBIFS has to report slightly less free space to meet the above
625  * expectations.
626  *
627  * This function assumes free space is made up of uncompressed data nodes and
628  * full index nodes (one per data node, tripled because we always allow enough
629  * space to write the index thrice).
630  *
631  * Note, the calculation is pessimistic, which means that most of the time
632  * UBIFS reports less space than it actually has.
633  */
634 long long ubifs_reported_space(const struct ubifs_info *c, long long free)
635 {
636 	int divisor, factor, f;
637 
638 	/*
639 	 * Reported space size is @free * X, where X is UBIFS block size
640 	 * divided by UBIFS block size + all overhead one data block
641 	 * introduces. The overhead is the node header + indexing overhead.
642 	 *
643 	 * Indexing overhead calculations are based on the following formula:
644 	 * I = N/(f - 1) + 1, where I - number of indexing nodes, N - number
645 	 * of data nodes, f - fanout. Because effective UBIFS fanout is twice
646 	 * as less than maximum fanout, we assume that each data node
647 	 * introduces 3 * @c->max_idx_node_sz / (@c->fanout/2 - 1) bytes.
648 	 * Note, the multiplier 3 is because UBIFS reserves thrice as more space
649 	 * for the index.
650 	 */
651 	f = c->fanout > 3 ? c->fanout >> 1 : 2;
652 	factor = UBIFS_BLOCK_SIZE;
653 	divisor = UBIFS_MAX_DATA_NODE_SZ;
654 	divisor += (c->max_idx_node_sz * 3) / (f - 1);
655 	free *= factor;
656 	return div_u64(free, divisor);
657 }
658 
659 #ifndef __UBOOT__
660 /**
661  * ubifs_get_free_space_nolock - return amount of free space.
662  * @c: UBIFS file-system description object
663  *
664  * This function calculates amount of free space to report to user-space.
665  *
666  * Because UBIFS may introduce substantial overhead (the index, node headers,
667  * alignment, wastage at the end of LEBs, etc), it cannot report real amount of
668  * free flash space it has (well, because not all dirty space is reclaimable,
669  * UBIFS does not actually know the real amount). If UBIFS did so, it would
670  * bread user expectations about what free space is. Users seem to accustomed
671  * to assume that if the file-system reports N bytes of free space, they would
672  * be able to fit a file of N bytes to the FS. This almost works for
673  * traditional file-systems, because they have way less overhead than UBIFS.
674  * So, to keep users happy, UBIFS tries to take the overhead into account.
675  */
676 long long ubifs_get_free_space_nolock(struct ubifs_info *c)
677 {
678 	int rsvd_idx_lebs, lebs;
679 	long long available, outstanding, free;
680 
681 	ubifs_assert(c->bi.min_idx_lebs == ubifs_calc_min_idx_lebs(c));
682 	outstanding = c->bi.data_growth + c->bi.dd_growth;
683 	available = ubifs_calc_available(c, c->bi.min_idx_lebs);
684 
685 	/*
686 	 * When reporting free space to user-space, UBIFS guarantees that it is
687 	 * possible to write a file of free space size. This means that for
688 	 * empty LEBs we may use more precise calculations than
689 	 * 'ubifs_calc_available()' is using. Namely, we know that in empty
690 	 * LEBs we would waste only @c->leb_overhead bytes, not @c->dark_wm.
691 	 * Thus, amend the available space.
692 	 *
693 	 * Note, the calculations below are similar to what we have in
694 	 * 'do_budget_space()', so refer there for comments.
695 	 */
696 	if (c->bi.min_idx_lebs > c->lst.idx_lebs)
697 		rsvd_idx_lebs = c->bi.min_idx_lebs - c->lst.idx_lebs;
698 	else
699 		rsvd_idx_lebs = 0;
700 	lebs = c->lst.empty_lebs + c->freeable_cnt + c->idx_gc_cnt -
701 	       c->lst.taken_empty_lebs;
702 	lebs -= rsvd_idx_lebs;
703 	available += lebs * (c->dark_wm - c->leb_overhead);
704 
705 	if (available > outstanding)
706 		free = ubifs_reported_space(c, available - outstanding);
707 	else
708 		free = 0;
709 	return free;
710 }
711 
712 /**
713  * ubifs_get_free_space - return amount of free space.
714  * @c: UBIFS file-system description object
715  *
716  * This function calculates and returns amount of free space to report to
717  * user-space.
718  */
719 long long ubifs_get_free_space(struct ubifs_info *c)
720 {
721 	long long free;
722 
723 	spin_lock(&c->space_lock);
724 	free = ubifs_get_free_space_nolock(c);
725 	spin_unlock(&c->space_lock);
726 
727 	return free;
728 }
729 #endif
730