linux/fs/ubifs/budget.c
<<
>>
Prefs
   1/*
   2 * This file is part of UBIFS.
   3 *
   4 * Copyright (C) 2006-2008 Nokia Corporation.
   5 *
   6 * This program is free software; you can redistribute it and/or modify it
   7 * under the terms of the GNU General Public License version 2 as published by
   8 * the Free Software Foundation.
   9 *
  10 * This program is distributed in the hope that it will be useful, but WITHOUT
  11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  12 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
  13 * more details.
  14 *
  15 * You should have received a copy of the GNU General Public License along with
  16 * this program; if not, write to the Free Software Foundation, Inc., 51
  17 * Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
  18 *
  19 * Authors: Adrian Hunter
  20 *          Artem Bityutskiy (Битюцкий Артём)
  21 */
  22
  23/*
  24 * This file implements the budgeting sub-system which is responsible for UBIFS
  25 * space management.
  26 *
  27 * Factors such as compression, wasted space at the ends of LEBs, space in other
  28 * journal heads, the effect of updates on the index, and so on, make it
  29 * impossible to accurately predict the amount of space needed. Consequently
  30 * approximations are used.
  31 */
  32
  33#include "ubifs.h"
  34#include <linux/writeback.h>
  35#include <linux/math64.h>
  36
  37/*
  38 * When pessimistic budget calculations say that there is no enough space,
  39 * UBIFS starts writing back dirty inodes and pages, doing garbage collection,
  40 * or committing. The below constant defines maximum number of times UBIFS
  41 * repeats the operations.
  42 */
  43#define MAX_MKSPC_RETRIES 3
  44
  45/*
  46 * The below constant defines amount of dirty pages which should be written
  47 * back at when trying to shrink the liability.
  48 */
  49#define NR_TO_WRITE 16
  50
  51/**
  52 * shrink_liability - write-back some dirty pages/inodes.
  53 * @c: UBIFS file-system description object
  54 * @nr_to_write: how many dirty pages to write-back
  55 *
  56 * This function shrinks UBIFS liability by means of writing back some amount
  57 * of dirty inodes and their pages.
  58 *
  59 * Note, this function synchronizes even VFS inodes which are locked
  60 * (@i_mutex) by the caller of the budgeting function, because write-back does
  61 * not touch @i_mutex.
  62 */
  63static void shrink_liability(struct ubifs_info *c, int nr_to_write)
  64{
  65        down_read(&c->vfs_sb->s_umount);
  66        writeback_inodes_sb(c->vfs_sb, WB_REASON_FS_FREE_SPACE);
  67        up_read(&c->vfs_sb->s_umount);
  68}
  69
  70/**
  71 * run_gc - run garbage collector.
  72 * @c: UBIFS file-system description object
  73 *
  74 * This function runs garbage collector to make some more free space. Returns
  75 * zero if a free LEB has been produced, %-EAGAIN if commit is required, and a
  76 * negative error code in case of failure.
  77 */
  78static int run_gc(struct ubifs_info *c)
  79{
  80        int err, lnum;
  81
  82        /* Make some free space by garbage-collecting dirty space */
  83        down_read(&c->commit_sem);
  84        lnum = ubifs_garbage_collect(c, 1);
  85        up_read(&c->commit_sem);
  86        if (lnum < 0)
  87                return lnum;
  88
  89        /* GC freed one LEB, return it to lprops */
  90        dbg_budg("GC freed LEB %d", lnum);
  91        err = ubifs_return_leb(c, lnum);
  92        if (err)
  93                return err;
  94        return 0;
  95}
  96
  97/**
  98 * get_liability - calculate current liability.
  99 * @c: UBIFS file-system description object
 100 *
 101 * This function calculates and returns current UBIFS liability, i.e. the
 102 * amount of bytes UBIFS has "promised" to write to the media.
 103 */
 104static long long get_liability(struct ubifs_info *c)
 105{
 106        long long liab;
 107
 108        spin_lock(&c->space_lock);
 109        liab = c->bi.idx_growth + c->bi.data_growth + c->bi.dd_growth;
 110        spin_unlock(&c->space_lock);
 111        return liab;
 112}
 113
 114/**
 115 * make_free_space - make more free space on the file-system.
 116 * @c: UBIFS file-system description object
 117 *
 118 * This function is called when an operation cannot be budgeted because there
 119 * is supposedly no free space. But in most cases there is some free space:
 120 *   o budgeting is pessimistic, so it always budgets more than it is actually
 121 *     needed, so shrinking the liability is one way to make free space - the
 122 *     cached data will take less space then it was budgeted for;
 123 *   o GC may turn some dark space into free space (budgeting treats dark space
 124 *     as not available);
 125 *   o commit may free some LEB, i.e., turn freeable LEBs into free LEBs.
 126 *
 127 * So this function tries to do the above. Returns %-EAGAIN if some free space
 128 * was presumably made and the caller has to re-try budgeting the operation.
 129 * Returns %-ENOSPC if it couldn't do more free space, and other negative error
 130 * codes on failures.
 131 */
 132static int make_free_space(struct ubifs_info *c)
 133{
 134        int err, retries = 0;
 135        long long liab1, liab2;
 136
 137        do {
 138                liab1 = get_liability(c);
 139                /*
 140                 * We probably have some dirty pages or inodes (liability), try
 141                 * to write them back.
 142                 */
 143                dbg_budg("liability %lld, run write-back", liab1);
 144                shrink_liability(c, NR_TO_WRITE);
 145
 146                liab2 = get_liability(c);
 147                if (liab2 < liab1)
 148                        return -EAGAIN;
 149
 150                dbg_budg("new liability %lld (not shrunk)", liab2);
 151
 152                /* Liability did not shrink again, try GC */
 153                dbg_budg("Run GC");
 154                err = run_gc(c);
 155                if (!err)
 156                        return -EAGAIN;
 157
 158                if (err != -EAGAIN && err != -ENOSPC)
 159                        /* Some real error happened */
 160                        return err;
 161
 162                dbg_budg("Run commit (retries %d)", retries);
 163                err = ubifs_run_commit(c);
 164                if (err)
 165                        return err;
 166        } while (retries++ < MAX_MKSPC_RETRIES);
 167
 168        return -ENOSPC;
 169}
 170
 171/**
 172 * ubifs_calc_min_idx_lebs - calculate amount of LEBs for the index.
 173 * @c: UBIFS file-system description object
 174 *
 175 * This function calculates and returns the number of LEBs which should be kept
 176 * for index usage.
 177 */
 178int ubifs_calc_min_idx_lebs(struct ubifs_info *c)
 179{
 180        int idx_lebs;
 181        long long idx_size;
 182
 183        idx_size = c->bi.old_idx_sz + c->bi.idx_growth + c->bi.uncommitted_idx;
 184        /* And make sure we have thrice the index size of space reserved */
 185        idx_size += idx_size << 1;
 186        /*
 187         * We do not maintain 'old_idx_size' as 'old_idx_lebs'/'old_idx_bytes'
 188         * pair, nor similarly the two variables for the new index size, so we
 189         * have to do this costly 64-bit division on fast-path.
 190         */
 191        idx_lebs = div_u64(idx_size + c->idx_leb_size - 1, c->idx_leb_size);
 192        /*
 193         * The index head is not available for the in-the-gaps method, so add an
 194         * extra LEB to compensate.
 195         */
 196        idx_lebs += 1;
 197        if (idx_lebs < MIN_INDEX_LEBS)
 198                idx_lebs = MIN_INDEX_LEBS;
 199        return idx_lebs;
 200}
 201
 202/**
 203 * ubifs_calc_available - calculate available FS space.
 204 * @c: UBIFS file-system description object
 205 * @min_idx_lebs: minimum number of LEBs reserved for the index
 206 *
 207 * This function calculates and returns amount of FS space available for use.
 208 */
 209long long ubifs_calc_available(const struct ubifs_info *c, int min_idx_lebs)
 210{
 211        int subtract_lebs;
 212        long long available;
 213
 214        available = c->main_bytes - c->lst.total_used;
 215
 216        /*
 217         * Now 'available' contains theoretically available flash space
 218         * assuming there is no index, so we have to subtract the space which
 219         * is reserved for the index.
 220         */
 221        subtract_lebs = min_idx_lebs;
 222
 223        /* Take into account that GC reserves one LEB for its own needs */
 224        subtract_lebs += 1;
 225
 226        /*
 227         * The GC journal head LEB is not really accessible. And since
 228         * different write types go to different heads, we may count only on
 229         * one head's space.
 230         */
 231        subtract_lebs += c->jhead_cnt - 1;
 232
 233        /* We also reserve one LEB for deletions, which bypass budgeting */
 234        subtract_lebs += 1;
 235
 236        available -= (long long)subtract_lebs * c->leb_size;
 237
 238        /* Subtract the dead space which is not available for use */
 239        available -= c->lst.total_dead;
 240
 241        /*
 242         * Subtract dark space, which might or might not be usable - it depends
 243         * on the data which we have on the media and which will be written. If
 244         * this is a lot of uncompressed or not-compressible data, the dark
 245         * space cannot be used.
 246         */
 247        available -= c->lst.total_dark;
 248
 249        /*
 250         * However, there is more dark space. The index may be bigger than
 251         * @min_idx_lebs. Those extra LEBs are assumed to be available, but
 252         * their dark space is not included in total_dark, so it is subtracted
 253         * here.
 254         */
 255        if (c->lst.idx_lebs > min_idx_lebs) {
 256                subtract_lebs = c->lst.idx_lebs - min_idx_lebs;
 257                available -= subtract_lebs * c->dark_wm;
 258        }
 259
 260        /* The calculations are rough and may end up with a negative number */
 261        return available > 0 ? available : 0;
 262}
 263
 264/**
 265 * can_use_rp - check whether the user is allowed to use reserved pool.
 266 * @c: UBIFS file-system description object
 267 *
 268 * UBIFS has so-called "reserved pool" which is flash space reserved
 269 * for the superuser and for uses whose UID/GID is recorded in UBIFS superblock.
 270 * This function checks whether current user is allowed to use reserved pool.
 271 * Returns %1  current user is allowed to use reserved pool and %0 otherwise.
 272 */
 273static int can_use_rp(struct ubifs_info *c)
 274{
 275        if (current_fsuid() == c->rp_uid || capable(CAP_SYS_RESOURCE) ||
 276            (c->rp_gid != 0 && in_group_p(c->rp_gid)))
 277                return 1;
 278        return 0;
 279}
 280
 281/**
 282 * do_budget_space - reserve flash space for index and data growth.
 283 * @c: UBIFS file-system description object
 284 *
 285 * This function makes sure UBIFS has enough free LEBs for index growth and
 286 * data.
 287 *
 288 * When budgeting index space, UBIFS reserves thrice as many LEBs as the index
 289 * would take if it was consolidated and written to the flash. This guarantees
 290 * that the "in-the-gaps" commit method always succeeds and UBIFS will always
 291 * be able to commit dirty index. So this function basically adds amount of
 292 * budgeted index space to the size of the current index, multiplies this by 3,
 293 * and makes sure this does not exceed the amount of free LEBs.
 294 *
 295 * Notes about @c->bi.min_idx_lebs and @c->lst.idx_lebs variables:
 296 * o @c->lst.idx_lebs is the number of LEBs the index currently uses. It might
 297 *    be large, because UBIFS does not do any index consolidation as long as
 298 *    there is free space. IOW, the index may take a lot of LEBs, but the LEBs
 299 *    will contain a lot of dirt.
 300 * o @c->bi.min_idx_lebs is the number of LEBS the index presumably takes. IOW,
 301 *    the index may be consolidated to take up to @c->bi.min_idx_lebs LEBs.
 302 *
 303 * This function returns zero in case of success, and %-ENOSPC in case of
 304 * failure.
 305 */
 306static int do_budget_space(struct ubifs_info *c)
 307{
 308        long long outstanding, available;
 309        int lebs, rsvd_idx_lebs, min_idx_lebs;
 310
 311        /* First budget index space */
 312        min_idx_lebs = ubifs_calc_min_idx_lebs(c);
 313
 314        /* Now 'min_idx_lebs' contains number of LEBs to reserve */
 315        if (min_idx_lebs > c->lst.idx_lebs)
 316                rsvd_idx_lebs = min_idx_lebs - c->lst.idx_lebs;
 317        else
 318                rsvd_idx_lebs = 0;
 319
 320        /*
 321         * The number of LEBs that are available to be used by the index is:
 322         *
 323         *    @c->lst.empty_lebs + @c->freeable_cnt + @c->idx_gc_cnt -
 324         *    @c->lst.taken_empty_lebs
 325         *
 326         * @c->lst.empty_lebs are available because they are empty.
 327         * @c->freeable_cnt are available because they contain only free and
 328         * dirty space, @c->idx_gc_cnt are available because they are index
 329         * LEBs that have been garbage collected and are awaiting the commit
 330         * before they can be used. And the in-the-gaps method will grab these
 331         * if it needs them. @c->lst.taken_empty_lebs are empty LEBs that have
 332         * already been allocated for some purpose.
 333         *
 334         * Note, @c->idx_gc_cnt is included to both @c->lst.empty_lebs (because
 335         * these LEBs are empty) and to @c->lst.taken_empty_lebs (because they
 336         * are taken until after the commit).
 337         *
 338         * Note, @c->lst.taken_empty_lebs may temporarily be higher by one
 339         * because of the way we serialize LEB allocations and budgeting. See a
 340         * comment in 'ubifs_find_free_space()'.
 341         */
 342        lebs = c->lst.empty_lebs + c->freeable_cnt + c->idx_gc_cnt -
 343               c->lst.taken_empty_lebs;
 344        if (unlikely(rsvd_idx_lebs > lebs)) {
 345                dbg_budg("out of indexing space: min_idx_lebs %d (old %d), "
 346                         "rsvd_idx_lebs %d", min_idx_lebs, c->bi.min_idx_lebs,
 347                         rsvd_idx_lebs);
 348                return -ENOSPC;
 349        }
 350
 351        available = ubifs_calc_available(c, min_idx_lebs);
 352        outstanding = c->bi.data_growth + c->bi.dd_growth;
 353
 354        if (unlikely(available < outstanding)) {
 355                dbg_budg("out of data space: available %lld, outstanding %lld",
 356                         available, outstanding);
 357                return -ENOSPC;
 358        }
 359
 360        if (available - outstanding <= c->rp_size && !can_use_rp(c))
 361                return -ENOSPC;
 362
 363        c->bi.min_idx_lebs = min_idx_lebs;
 364        return 0;
 365}
 366
 367/**
 368 * calc_idx_growth - calculate approximate index growth from budgeting request.
 369 * @c: UBIFS file-system description object
 370 * @req: budgeting request
 371 *
 372 * For now we assume each new node adds one znode. But this is rather poor
 373 * approximation, though.
 374 */
 375static int calc_idx_growth(const struct ubifs_info *c,
 376                           const struct ubifs_budget_req *req)
 377{
 378        int znodes;
 379
 380        znodes = req->new_ino + (req->new_page << UBIFS_BLOCKS_PER_PAGE_SHIFT) +
 381                 req->new_dent;
 382        return znodes * c->max_idx_node_sz;
 383}
 384
 385/**
 386 * calc_data_growth - calculate approximate amount of new data from budgeting
 387 * request.
 388 * @c: UBIFS file-system description object
 389 * @req: budgeting request
 390 */
 391static int calc_data_growth(const struct ubifs_info *c,
 392                            const struct ubifs_budget_req *req)
 393{
 394        int data_growth;
 395
 396        data_growth = req->new_ino  ? c->bi.inode_budget : 0;
 397        if (req->new_page)
 398                data_growth += c->bi.page_budget;
 399        if (req->new_dent)
 400                data_growth += c->bi.dent_budget;
 401        data_growth += req->new_ino_d;
 402        return data_growth;
 403}
 404
 405/**
 406 * calc_dd_growth - calculate approximate amount of data which makes other data
 407 * dirty from budgeting request.
 408 * @c: UBIFS file-system description object
 409 * @req: budgeting request
 410 */
 411static int calc_dd_growth(const struct ubifs_info *c,
 412                          const struct ubifs_budget_req *req)
 413{
 414        int dd_growth;
 415
 416        dd_growth = req->dirtied_page ? c->bi.page_budget : 0;
 417
 418        if (req->dirtied_ino)
 419                dd_growth += c->bi.inode_budget << (req->dirtied_ino - 1);
 420        if (req->mod_dent)
 421                dd_growth += c->bi.dent_budget;
 422        dd_growth += req->dirtied_ino_d;
 423        return dd_growth;
 424}
 425
 426/**
 427 * ubifs_budget_space - ensure there is enough space to complete an operation.
 428 * @c: UBIFS file-system description object
 429 * @req: budget request
 430 *
 431 * This function allocates budget for an operation. It uses pessimistic
 432 * approximation of how much flash space the operation needs. The goal of this
 433 * function is to make sure UBIFS always has flash space to flush all dirty
 434 * pages, dirty inodes, and dirty znodes (liability). This function may force
 435 * commit, garbage-collection or write-back. Returns zero in case of success,
 436 * %-ENOSPC if there is no free space and other negative error codes in case of
 437 * failures.
 438 */
 439int ubifs_budget_space(struct ubifs_info *c, struct ubifs_budget_req *req)
 440{
 441        int uninitialized_var(cmt_retries), uninitialized_var(wb_retries);
 442        int err, idx_growth, data_growth, dd_growth, retried = 0;
 443
 444        ubifs_assert(req->new_page <= 1);
 445        ubifs_assert(req->dirtied_page <= 1);
 446        ubifs_assert(req->new_dent <= 1);
 447        ubifs_assert(req->mod_dent <= 1);
 448        ubifs_assert(req->new_ino <= 1);
 449        ubifs_assert(req->new_ino_d <= UBIFS_MAX_INO_DATA);
 450        ubifs_assert(req->dirtied_ino <= 4);
 451        ubifs_assert(req->dirtied_ino_d <= UBIFS_MAX_INO_DATA * 4);
 452        ubifs_assert(!(req->new_ino_d & 7));
 453        ubifs_assert(!(req->dirtied_ino_d & 7));
 454
 455        data_growth = calc_data_growth(c, req);
 456        dd_growth = calc_dd_growth(c, req);
 457        if (!data_growth && !dd_growth)
 458                return 0;
 459        idx_growth = calc_idx_growth(c, req);
 460
 461again:
 462        spin_lock(&c->space_lock);
 463        ubifs_assert(c->bi.idx_growth >= 0);
 464        ubifs_assert(c->bi.data_growth >= 0);
 465        ubifs_assert(c->bi.dd_growth >= 0);
 466
 467        if (unlikely(c->bi.nospace) && (c->bi.nospace_rp || !can_use_rp(c))) {
 468                dbg_budg("no space");
 469                spin_unlock(&c->space_lock);
 470                return -ENOSPC;
 471        }
 472
 473        c->bi.idx_growth += idx_growth;
 474        c->bi.data_growth += data_growth;
 475        c->bi.dd_growth += dd_growth;
 476
 477        err = do_budget_space(c);
 478        if (likely(!err)) {
 479                req->idx_growth = idx_growth;
 480                req->data_growth = data_growth;
 481                req->dd_growth = dd_growth;
 482                spin_unlock(&c->space_lock);
 483                return 0;
 484        }
 485
 486        /* Restore the old values */
 487        c->bi.idx_growth -= idx_growth;
 488        c->bi.data_growth -= data_growth;
 489        c->bi.dd_growth -= dd_growth;
 490        spin_unlock(&c->space_lock);
 491
 492        if (req->fast) {
 493                dbg_budg("no space for fast budgeting");
 494                return err;
 495        }
 496
 497        err = make_free_space(c);
 498        cond_resched();
 499        if (err == -EAGAIN) {
 500                dbg_budg("try again");
 501                goto again;
 502        } else if (err == -ENOSPC) {
 503                if (!retried) {
 504                        retried = 1;
 505                        dbg_budg("-ENOSPC, but anyway try once again");
 506                        goto again;
 507                }
 508                dbg_budg("FS is full, -ENOSPC");
 509                c->bi.nospace = 1;
 510                if (can_use_rp(c) || c->rp_size == 0)
 511                        c->bi.nospace_rp = 1;
 512                smp_wmb();
 513        } else
 514                ubifs_err("cannot budget space, error %d", err);
 515        return err;
 516}
 517
 518/**
 519 * ubifs_release_budget - release budgeted free space.
 520 * @c: UBIFS file-system description object
 521 * @req: budget request
 522 *
 523 * This function releases the space budgeted by 'ubifs_budget_space()'. Note,
 524 * since the index changes (which were budgeted for in @req->idx_growth) will
 525 * only be written to the media on commit, this function moves the index budget
 526 * from @c->bi.idx_growth to @c->bi.uncommitted_idx. The latter will be zeroed
 527 * by the commit operation.
 528 */
 529void ubifs_release_budget(struct ubifs_info *c, struct ubifs_budget_req *req)
 530{
 531        ubifs_assert(req->new_page <= 1);
 532        ubifs_assert(req->dirtied_page <= 1);
 533        ubifs_assert(req->new_dent <= 1);
 534        ubifs_assert(req->mod_dent <= 1);
 535        ubifs_assert(req->new_ino <= 1);
 536        ubifs_assert(req->new_ino_d <= UBIFS_MAX_INO_DATA);
 537        ubifs_assert(req->dirtied_ino <= 4);
 538        ubifs_assert(req->dirtied_ino_d <= UBIFS_MAX_INO_DATA * 4);
 539        ubifs_assert(!(req->new_ino_d & 7));
 540        ubifs_assert(!(req->dirtied_ino_d & 7));
 541        if (!req->recalculate) {
 542                ubifs_assert(req->idx_growth >= 0);
 543                ubifs_assert(req->data_growth >= 0);
 544                ubifs_assert(req->dd_growth >= 0);
 545        }
 546
 547        if (req->recalculate) {
 548                req->data_growth = calc_data_growth(c, req);
 549                req->dd_growth = calc_dd_growth(c, req);
 550                req->idx_growth = calc_idx_growth(c, req);
 551        }
 552
 553        if (!req->data_growth && !req->dd_growth)
 554                return;
 555
 556        c->bi.nospace = c->bi.nospace_rp = 0;
 557        smp_wmb();
 558
 559        spin_lock(&c->space_lock);
 560        c->bi.idx_growth -= req->idx_growth;
 561        c->bi.uncommitted_idx += req->idx_growth;
 562        c->bi.data_growth -= req->data_growth;
 563        c->bi.dd_growth -= req->dd_growth;
 564        c->bi.min_idx_lebs = ubifs_calc_min_idx_lebs(c);
 565
 566        ubifs_assert(c->bi.idx_growth >= 0);
 567        ubifs_assert(c->bi.data_growth >= 0);
 568        ubifs_assert(c->bi.dd_growth >= 0);
 569        ubifs_assert(c->bi.min_idx_lebs < c->main_lebs);
 570        ubifs_assert(!(c->bi.idx_growth & 7));
 571        ubifs_assert(!(c->bi.data_growth & 7));
 572        ubifs_assert(!(c->bi.dd_growth & 7));
 573        spin_unlock(&c->space_lock);
 574}
 575
 576/**
 577 * ubifs_convert_page_budget - convert budget of a new page.
 578 * @c: UBIFS file-system description object
 579 *
 580 * This function converts budget which was allocated for a new page of data to
 581 * the budget of changing an existing page of data. The latter is smaller than
 582 * the former, so this function only does simple re-calculation and does not
 583 * involve any write-back.
 584 */
 585void ubifs_convert_page_budget(struct ubifs_info *c)
 586{
 587        spin_lock(&c->space_lock);
 588        /* Release the index growth reservation */
 589        c->bi.idx_growth -= c->max_idx_node_sz << UBIFS_BLOCKS_PER_PAGE_SHIFT;
 590        /* Release the data growth reservation */
 591        c->bi.data_growth -= c->bi.page_budget;
 592        /* Increase the dirty data growth reservation instead */
 593        c->bi.dd_growth += c->bi.page_budget;
 594        /* And re-calculate the indexing space reservation */
 595        c->bi.min_idx_lebs = ubifs_calc_min_idx_lebs(c);
 596        spin_unlock(&c->space_lock);
 597}
 598
 599/**
 600 * ubifs_release_dirty_inode_budget - release dirty inode budget.
 601 * @c: UBIFS file-system description object
 602 * @ui: UBIFS inode to release the budget for
 603 *
 604 * This function releases budget corresponding to a dirty inode. It is usually
 605 * called when after the inode has been written to the media and marked as
 606 * clean. It also causes the "no space" flags to be cleared.
 607 */
 608void ubifs_release_dirty_inode_budget(struct ubifs_info *c,
 609                                      struct ubifs_inode *ui)
 610{
 611        struct ubifs_budget_req req;
 612
 613        memset(&req, 0, sizeof(struct ubifs_budget_req));
 614        /* The "no space" flags will be cleared because dd_growth is > 0 */
 615        req.dd_growth = c->bi.inode_budget + ALIGN(ui->data_len, 8);
 616        ubifs_release_budget(c, &req);
 617}
 618
 619/**
 620 * ubifs_reported_space - calculate reported free space.
 621 * @c: the UBIFS file-system description object
 622 * @free: amount of free space
 623 *
 624 * This function calculates amount of free space which will be reported to
 625 * user-space. User-space application tend to expect that if the file-system
 626 * (e.g., via the 'statfs()' call) reports that it has N bytes available, they
 627 * are able to write a file of size N. UBIFS attaches node headers to each data
 628 * node and it has to write indexing nodes as well. This introduces additional
 629 * overhead, and UBIFS has to report slightly less free space to meet the above
 630 * expectations.
 631 *
 632 * This function assumes free space is made up of uncompressed data nodes and
 633 * full index nodes (one per data node, tripled because we always allow enough
 634 * space to write the index thrice).
 635 *
 636 * Note, the calculation is pessimistic, which means that most of the time
 637 * UBIFS reports less space than it actually has.
 638 */
 639long long ubifs_reported_space(const struct ubifs_info *c, long long free)
 640{
 641        int divisor, factor, f;
 642
 643        /*
 644         * Reported space size is @free * X, where X is UBIFS block size
 645         * divided by UBIFS block size + all overhead one data block
 646         * introduces. The overhead is the node header + indexing overhead.
 647         *
 648         * Indexing overhead calculations are based on the following formula:
 649         * I = N/(f - 1) + 1, where I - number of indexing nodes, N - number
 650         * of data nodes, f - fanout. Because effective UBIFS fanout is twice
 651         * as less than maximum fanout, we assume that each data node
 652         * introduces 3 * @c->max_idx_node_sz / (@c->fanout/2 - 1) bytes.
 653         * Note, the multiplier 3 is because UBIFS reserves thrice as more space
 654         * for the index.
 655         */
 656        f = c->fanout > 3 ? c->fanout >> 1 : 2;
 657        factor = UBIFS_BLOCK_SIZE;
 658        divisor = UBIFS_MAX_DATA_NODE_SZ;
 659        divisor += (c->max_idx_node_sz * 3) / (f - 1);
 660        free *= factor;
 661        return div_u64(free, divisor);
 662}
 663
 664/**
 665 * ubifs_get_free_space_nolock - return amount of free space.
 666 * @c: UBIFS file-system description object
 667 *
 668 * This function calculates amount of free space to report to user-space.
 669 *
 670 * Because UBIFS may introduce substantial overhead (the index, node headers,
 671 * alignment, wastage at the end of LEBs, etc), it cannot report real amount of
 672 * free flash space it has (well, because not all dirty space is reclaimable,
 673 * UBIFS does not actually know the real amount). If UBIFS did so, it would
 674 * bread user expectations about what free space is. Users seem to accustomed
 675 * to assume that if the file-system reports N bytes of free space, they would
 676 * be able to fit a file of N bytes to the FS. This almost works for
 677 * traditional file-systems, because they have way less overhead than UBIFS.
 678 * So, to keep users happy, UBIFS tries to take the overhead into account.
 679 */
 680long long ubifs_get_free_space_nolock(struct ubifs_info *c)
 681{
 682        int rsvd_idx_lebs, lebs;
 683        long long available, outstanding, free;
 684
 685        ubifs_assert(c->bi.min_idx_lebs == ubifs_calc_min_idx_lebs(c));
 686        outstanding = c->bi.data_growth + c->bi.dd_growth;
 687        available = ubifs_calc_available(c, c->bi.min_idx_lebs);
 688
 689        /*
 690         * When reporting free space to user-space, UBIFS guarantees that it is
 691         * possible to write a file of free space size. This means that for
 692         * empty LEBs we may use more precise calculations than
 693         * 'ubifs_calc_available()' is using. Namely, we know that in empty
 694         * LEBs we would waste only @c->leb_overhead bytes, not @c->dark_wm.
 695         * Thus, amend the available space.
 696         *
 697         * Note, the calculations below are similar to what we have in
 698         * 'do_budget_space()', so refer there for comments.
 699         */
 700        if (c->bi.min_idx_lebs > c->lst.idx_lebs)
 701                rsvd_idx_lebs = c->bi.min_idx_lebs - c->lst.idx_lebs;
 702        else
 703                rsvd_idx_lebs = 0;
 704        lebs = c->lst.empty_lebs + c->freeable_cnt + c->idx_gc_cnt -
 705               c->lst.taken_empty_lebs;
 706        lebs -= rsvd_idx_lebs;
 707        available += lebs * (c->dark_wm - c->leb_overhead);
 708
 709        if (available > outstanding)
 710                free = ubifs_reported_space(c, available - outstanding);
 711        else
 712                free = 0;
 713        return free;
 714}
 715
 716/**
 717 * ubifs_get_free_space - return amount of free space.
 718 * @c: UBIFS file-system description object
 719 *
 720 * This function calculates and returns amount of free space to report to
 721 * user-space.
 722 */
 723long long ubifs_get_free_space(struct ubifs_info *c)
 724{
 725        long long free;
 726
 727        spin_lock(&c->space_lock);
 728        free = ubifs_get_free_space_nolock(c);
 729        spin_unlock(&c->space_lock);
 730
 731        return free;
 732}
 733
lxr.linux.no kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.