/* * This file is part of UBIFS. * * Copyright (C) 2006-2008 Nokia Corporation. * * This program is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 as published by * the Free Software Foundation. * * This program is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for * more details. * * You should have received a copy of the GNU General Public License along with * this program; if not, write to the Free Software Foundation, Inc., 51 * Franklin St, Fifth Floor, Boston, MA 02110-1301 USA * * Authors: Adrian Hunter * Artem Bityutskiy (Битюцкий Артём) */ /* * This file implements the budgeting sub-system which is responsible for UBIFS * space management. * * Factors such as compression, wasted space at the ends of LEBs, space in other * journal heads, the effect of updates on the index, and so on, make it * impossible to accurately predict the amount of space needed. Consequently * approximations are used. */ #include "ubifs.h" #include <linux/writeback.h> #include <asm/div64.h> /* * When pessimistic budget calculations say that there is no enough space, * UBIFS starts writing back dirty inodes and pages, doing garbage collection, * or committing. The below constants define maximum number of times UBIFS * repeats the operations. */ #define MAX_SHRINK_RETRIES 8 #define MAX_GC_RETRIES 4 #define MAX_CMT_RETRIES 2 #define MAX_NOSPC_RETRIES 1 /* * The below constant defines amount of dirty pages which should be written * back at when trying to shrink the liability. */ #define NR_TO_WRITE 16 /** * struct retries_info - information about re-tries while making free space. * @prev_liability: previous liability * @shrink_cnt: how many times the liability was shrinked * @shrink_retries: count of liability shrink re-tries (increased when * liability does not shrink) * @try_gc: GC should be tried first * @gc_retries: how many times GC was run * @cmt_retries: how many times commit has been done * @nospc_retries: how many times GC returned %-ENOSPC * * Since we consider budgeting to be the fast-path, and this structure has to * be allocated on stack and zeroed out, we make it smaller using bit-fields. */ struct retries_info { long long prev_liability; unsigned int shrink_cnt; unsigned int shrink_retries:5; unsigned int try_gc:1; unsigned int gc_retries:4; unsigned int cmt_retries:3; unsigned int nospc_retries:1; }; /** * shrink_liability - write-back some dirty pages/inodes. * @c: UBIFS file-system description object * @nr_to_write: how many dirty pages to write-back * * This function shrinks UBIFS liability by means of writing back some amount * of dirty inodes and their pages. Returns the amount of pages which were * written back. The returned value does not include dirty inodes which were * synchronized. * * Note, this function synchronizes even VFS inodes which are locked * (@i_mutex) by the caller of the budgeting function, because write-back does * not touch @i_mutex. */ static int shrink_liability(struct ubifs_info *c, int nr_to_write) { int nr_written; struct writeback_control wbc = { .sync_mode = WB_SYNC_NONE, .range_end = LLONG_MAX, .nr_to_write = nr_to_write, }; generic_sync_sb_inodes(c->vfs_sb, &wbc); nr_written = nr_to_write - wbc.nr_to_write; if (!nr_written) { /* * Re-try again but wait on pages/inodes which are being * written-back concurrently (e.g., by pdflush). */ memset(&wbc, 0, sizeof(struct writeback_control)); wbc.sync_mode = WB_SYNC_ALL; wbc.range_end = LLONG_MAX; wbc.nr_to_write = nr_to_write; generic_sync_sb_inodes(c->vfs_sb, &wbc); nr_written = nr_to_write - wbc.nr_to_write; } dbg_budg("%d pages were written back", nr_written); return nr_written; } /** * run_gc - run garbage collector. * @c: UBIFS file-system description object * * This function runs garbage collector to make some more free space. Returns * zero if a free LEB has been produced, %-EAGAIN if commit is required, and a * negative error code in case of failure. */ static int run_gc(struct ubifs_info *c) { int err, lnum; /* Make some free space by garbage-collecting dirty space */ down_read(&c->commit_sem); lnum = ubifs_garbage_collect(c, 1); up_read(&c->commit_sem); if (lnum < 0) return lnum; /* GC freed one LEB, return it to lprops */ dbg_budg("GC freed LEB %d", lnum); err = ubifs_return_leb(c, lnum); if (err) return err; return 0; } /** * make_free_space - make more free space on the file-system. * @c: UBIFS file-system description object * @ri: information about previous invocations of this function * * This function is called when an operation cannot be budgeted because there * is supposedly no free space. But in most cases there is some free space: * o budgeting is pessimistic, so it always budgets more then it is actually * needed, so shrinking the liability is one way to make free space - the * cached data will take less space then it was budgeted for; * o GC may turn some dark space into free space (budgeting treats dark space * as not available); * o commit may free some LEB, i.e., turn freeable LEBs into free LEBs. * * So this function tries to do the above. Returns %-EAGAIN if some free space * was presumably made and the caller has to re-try budgeting the operation. * Returns %-ENOSPC if it couldn't do more free space, and other negative error * codes on failures. */ static int make_free_space(struct ubifs_info *c, struct retries_info *ri) { int err; /* * If we have some dirty pages and inodes (liability), try to write * them back unless this was tried too many times without effect * already. */ if (ri->shrink_retries < MAX_SHRINK_RETRIES && !ri->try_gc) { long long liability; spin_lock(&c->space_lock); liability = c->budg_idx_growth + c->budg_data_growth + c->budg_dd_growth; spin_unlock(&c->space_lock); if (ri->prev_liability >= liability) { /* Liability does not shrink, next time try GC then */ ri->shrink_retries += 1; if (ri->gc_retries < MAX_GC_RETRIES) ri->try_gc = 1; dbg_budg("liability did not shrink: retries %d of %d", ri->shrink_retries, MAX_SHRINK_RETRIES); } dbg_budg("force write-back (count %d)", ri->shrink_cnt); shrink_liability(c, NR_TO_WRITE + ri->shrink_cnt); ri->prev_liability = liability; ri->shrink_cnt += 1; return -EAGAIN; } /* * Try to run garbage collector unless it was already tried too many * times. */ if (ri->gc_retries < MAX_GC_RETRIES) { ri->gc_retries += 1; dbg_budg("run GC, retries %d of %d", ri->gc_retries, MAX_GC_RETRIES); ri->try_gc = 0; err = run_gc(c); if (!err) return -EAGAIN; if (err == -EAGAIN) { dbg_budg("GC asked to commit"); err = ubifs_run_commit(c); if (err) return err; return -EAGAIN; } if (err != -ENOSPC) return err; /* * GC could not make any progress. If this is the first time, * then it makes sense to try to commit, because it might make * some dirty space. */ dbg_budg("GC returned -ENOSPC, retries %d", ri->nospc_retries); if (ri->nospc_retries >= MAX_NOSPC_RETRIES) return err; ri->nospc_retries += 1; } /* Neither GC nor write-back helped, try to commit */ if (ri->cmt_retries < MAX_CMT_RETRIES) { ri->cmt_retries += 1; dbg_budg("run commit, retries %d of %d", ri->cmt_retries, MAX_CMT_RETRIES); err = ubifs_run_commit(c); if (err) return err; return -EAGAIN; } return -ENOSPC; } /** * ubifs_calc_min_idx_lebs - calculate amount of eraseblocks for the index. * @c: UBIFS file-system description object * * This function calculates and returns the number of eraseblocks which should * be kept for index usage. */ int ubifs_calc_min_idx_lebs(struct ubifs_info *c) { int ret; uint64_t idx_size; idx_size = c->old_idx_sz + c->budg_idx_growth + c->budg_uncommitted_idx; /* And make sure we have thrice the index size of space reserved */ idx_size = idx_size + (idx_size << 1); /* * We do not maintain 'old_idx_size' as 'old_idx_lebs'/'old_idx_bytes' * pair, nor similarly the two variables for the new index size, so we * have to do this costly 64-bit division on fast-path. */ if (do_div(idx_size, c->leb_size - c->max_idx_node_sz)) ret = idx_size + 1; else ret = idx_size; /* * The index head is not available for the in-the-gaps method, so add an * extra LEB to compensate. */ ret += 1; /* * At present the index needs at least 2 LEBs: one for the index head * and one for in-the-gaps method (which currently does not cater for * the index head and so excludes it from consideration). */ if (ret < 2) ret = 2; return ret; } /** * ubifs_calc_available - calculate available FS space. * @c: UBIFS file-system description object * @min_idx_lebs: minimum number of LEBs reserved for the index * * This function calculates and returns amount of FS space available for use. */ long long ubifs_calc_available(const struct ubifs_info *c, int min_idx_lebs) { int subtract_lebs; long long available; available = c->main_bytes - c->lst.total_used; /* * Now 'available' contains theoretically available flash space * assuming there is no index, so we have to subtract the space which * is reserved for the index. */ subtract_lebs = min_idx_lebs; /* Take into account that GC reserves one LEB for its own needs */ subtract_lebs += 1; /* * The GC journal head LEB is not really accessible. And since * different write types go to different heads, we may count only on * one head's space. */ subtract_lebs += c->jhead_cnt - 1; /* We also reserve one LEB for deletions, which bypass budgeting */ subtract_lebs += 1; available -= (long long)subtract_lebs * c->leb_size; /* Subtract the dead space which is not available for use */ available -= c->lst.total_dead; /* * Subtract dark space, which might or might not be usable - it depends * on the data which we have on the media and which will be written. If * this is a lot of uncompressed or not-compressible data, the dark * space cannot be used. */ available -= c->lst.total_dark; /* * However, there is more dark space. The index may be bigger than * @min_idx_lebs. Those extra LEBs are assumed to be available, but * their dark space is not included in total_dark, so it is subtracted * here. */ if (c->lst.idx_lebs > min_idx_lebs) { subtract_lebs = c->lst.idx_lebs - min_idx_lebs; available -= subtract_lebs * c->dark_wm; } /* The calculations are rough and may end up with a negative number */ return available > 0 ? available : 0; } /** * can_use_rp - check whether the user is allowed to use reserved pool. * @c: UBIFS file-system description object * * UBIFS has so-called "reserved pool" which is flash space reserved * for the superuser and for uses whose UID/GID is recorded in UBIFS superblock. * This function checks whether current user is allowed to use reserved pool. * Returns %1 current user is allowed to use reserved pool and %0 otherwise. */ static int can_use_rp(struct ubifs_info *c) { if (current->fsuid == c->rp_uid || capable(CAP_SYS_RESOURCE) || (c->rp_gid != 0 && in_group_p(c->rp_gid))) return 1; return 0; } /** * do_budget_space - reserve flash space for index and data growth. * @c: UBIFS file-system description object * * This function makes sure UBIFS has enough free eraseblocks for index growth * and data. * * When budgeting index space, UBIFS reserves thrice as many LEBs as the index * would take if it was consolidated and written to the flash. This guarantees * that the "in-the-gaps" commit method always succeeds and UBIFS will always * be able to commit dirty index. So this function basically adds amount of * budgeted index space to the size of the current index, multiplies this by 3, * and makes sure this does not exceed the amount of free eraseblocks. * * Notes about @c->min_idx_lebs and @c->lst.idx_lebs variables: * o @c->lst.idx_lebs is the number of LEBs the index currently uses. It might * be large, because UBIFS does not do any index consolidation as long as * there is free space. IOW, the index may take a lot of LEBs, but the LEBs * will contain a lot of dirt. * o @c->min_idx_lebs is the the index presumably takes. IOW, the index may be * consolidated to take up to @c->min_idx_lebs LEBs. * * This function returns zero in case of success, and %-ENOSPC in case of * failure. */ static int do_budget_space(struct ubifs_info *c) { long long outstanding, available; int lebs, rsvd_idx_lebs, min_idx_lebs; /* First budget index space */ min_idx_lebs = ubifs_calc_min_idx_lebs(c); /* Now 'min_idx_lebs' contains number of LEBs to reserve */ if (min_idx_lebs > c->lst.idx_lebs) rsvd_idx_lebs = min_idx_lebs - c->lst.idx_lebs; else rsvd_idx_lebs = 0; /* * The number of LEBs that are available to be used by the index is: * * @c->lst.empty_lebs + @c->freeable_cnt + @c->idx_gc_cnt - * @c->lst.taken_empty_lebs * * @empty_lebs are available because they are empty. @freeable_cnt are * available because they contain only free and dirty space and the * index allocation always occurs after wbufs are synch'ed. * @idx_gc_cnt are available because they are index LEBs that have been * garbage collected (including trivial GC) and are awaiting the commit * before they can be unmapped - note that the in-the-gaps method will * grab these if it needs them. @taken_empty_lebs are empty_lebs that * have already been allocated for some purpose (also includes those * LEBs on the @idx_gc list). * * Note, @taken_empty_lebs may temporarily be higher by one because of * the way we serialize LEB allocations and budgeting. See a comment in * 'ubifs_find_free_space()'. */ lebs = c->lst.empty_lebs + c->freeable_cnt + c->idx_gc_cnt - c->lst.taken_empty_lebs; if (unlikely(rsvd_idx_lebs > lebs)) { dbg_budg("out of indexing space: min_idx_lebs %d (old %d), " "rsvd_idx_lebs %d", min_idx_lebs, c->min_idx_lebs, rsvd_idx_lebs); return -ENOSPC; } available = ubifs_calc_available(c, min_idx_lebs); outstanding = c->budg_data_growth + c->budg_dd_growth; if (unlikely(available < outstanding)) { dbg_budg("out of data space: available %lld, outstanding %lld", available, outstanding); return -ENOSPC; } if (available - outstanding <= c->rp_size && !can_use_rp(c)) return -ENOSPC; c->min_idx_lebs = min_idx_lebs; return 0; } /** * calc_idx_growth - calculate approximate index growth from budgeting request. * @c: UBIFS file-system description object * @req: budgeting request * * For now we assume each new node adds one znode. But this is rather poor * approximation, though. */ static int calc_idx_growth(const struct ubifs_info *c, const struct ubifs_budget_req *req) { int znodes; znodes = req->new_ino + (req->new_page << UBIFS_BLOCKS_PER_PAGE_SHIFT) + req->new_dent; return znodes * c->max_idx_node_sz; } /** * calc_data_growth - calculate approximate amount of new data from budgeting * request. * @c: UBIFS file-system description object * @req: budgeting request */ static int calc_data_growth(const struct ubifs_info *c, const struct ubifs_budget_req *req) { int data_growth; data_growth = req->new_ino ? c->inode_budget : 0; if (req->new_page) data_growth += c->page_budget; if (req->new_dent) data_growth += c->dent_budget; data_growth += req->new_ino_d; return data_growth; } /** * calc_dd_growth - calculate approximate amount of data which makes other data * dirty from budgeting request. * @c: UBIFS file-system description object * @req: budgeting request */ static int calc_dd_growth(const struct ubifs_info *c, const struct ubifs_budget_req *req) { int dd_growth; dd_growth = req->dirtied_page ? c->page_budget : 0; if (req->dirtied_ino) dd_growth += c->inode_budget << (req->dirtied_ino - 1); if (req->mod_dent) dd_growth += c->dent_budget; dd_growth += req->dirtied_ino_d; return dd_growth; } /** * ubifs_budget_space - ensure there is enough space to complete an operation. * @c: UBIFS file-system description object * @req: budget request * * This function allocates budget for an operation. It uses pessimistic * approximation of how much flash space the operation needs. The goal of this * function is to make sure UBIFS always has flash space to flush all dirty * pages, dirty inodes, and dirty znodes (liability). This function may force * commit, garbage-collection or write-back. Returns zero in case of success, * %-ENOSPC if there is no free space and other negative error codes in case of * failures. */ int ubifs_budget_space(struct ubifs_info *c, struct ubifs_budget_req *req) { int uninitialized_var(cmt_retries), uninitialized_var(wb_retries); int err, idx_growth, data_growth, dd_growth; struct retries_info ri; ubifs_assert(req->new_page <= 1); ubifs_assert(req->dirtied_page <= 1); ubifs_assert(req->new_dent <= 1); ubifs_assert(req->mod_dent <= 1); ubifs_assert(req->new_ino <= 1); ubifs_assert(req->new_ino_d <= UBIFS_MAX_INO_DATA); ubifs_assert(req->dirtied_ino <= 4); ubifs_assert(req->dirtied_ino_d <= UBIFS_MAX_INO_DATA * 4); ubifs_assert(!(req->new_ino_d & 7)); ubifs_assert(!(req->dirtied_ino_d & 7)); data_growth = calc_data_growth(c, req); dd_growth = calc_dd_growth(c, req); if (!data_growth && !dd_growth) return 0; idx_growth = calc_idx_growth(c, req); memset(&ri, 0, sizeof(struct retries_info)); again: spin_lock(&c->space_lock); ubifs_assert(c->budg_idx_growth >= 0); ubifs_assert(c->budg_data_growth >= 0); ubifs_assert(c->budg_dd_growth >= 0); if (unlikely(c->nospace) && (c->nospace_rp || !can_use_rp(c))) { dbg_budg("no space"); spin_unlock(&c->space_lock); return -ENOSPC; } c->budg_idx_growth += idx_growth; c->budg_data_growth += data_growth; c->budg_dd_growth += dd_growth; err = do_budget_space(c); if (likely(!err)) { req->idx_growth = idx_growth; req->data_growth = data_growth; req->dd_growth = dd_growth; spin_unlock(&c->space_lock); return 0; } /* Restore the old values */ c->budg_idx_growth -= idx_growth; c->budg_data_growth -= data_growth; c->budg_dd_growth -= dd_growth; spin_unlock(&c->space_lock); if (req->fast) { dbg_budg("no space for fast budgeting"); return err; } err = make_free_space(c, &ri); if (err == -EAGAIN) { dbg_budg("try again"); cond_resched(); goto again; } else if (err == -ENOSPC) { dbg_budg("FS is full, -ENOSPC"); c->nospace = 1; if (can_use_rp(c) || c->rp_size == 0) c->nospace_rp = 1; smp_wmb(); } else ubifs_err("cannot budget space, error %d", err); return err; } /** * ubifs_release_budget - release budgeted free space. * @c: UBIFS file-system description object * @req: budget request * * This function releases the space budgeted by 'ubifs_budget_space()'. Note, * since the index changes (which were budgeted for in @req->idx_growth) will * only be written to the media on commit, this function moves the index budget * from @c->budg_idx_growth to @c->budg_uncommitted_idx. The latter will be * zeroed by the commit operation. */ void ubifs_release_budget(struct ubifs_info *c, struct ubifs_budget_req *req) { ubifs_assert(req->new_page <= 1); ubifs_assert(req->dirtied_page <= 1); ubifs_assert(req->new_dent <= 1); ubifs_assert(req->mod_dent <= 1); ubifs_assert(req->new_ino <= 1); ubifs_assert(req->new_ino_d <= UBIFS_MAX_INO_DATA); ubifs_assert(req->dirtied_ino <= 4); ubifs_assert(req->dirtied_ino_d <= UBIFS_MAX_INO_DATA * 4); ubifs_assert(!(req->new_ino_d & 7)); ubifs_assert(!(req->dirtied_ino_d & 7)); if (!req->recalculate) { ubifs_assert(req->idx_growth >= 0); ubifs_assert(req->data_growth >= 0); ubifs_assert(req->dd_growth >= 0); } if (req->recalculate) { req->data_growth = calc_data_growth(c, req); req->dd_growth = calc_dd_growth(c, req); req->idx_growth = calc_idx_growth(c, req); } if (!req->data_growth && !req->dd_growth) return; c->nospace = c->nospace_rp = 0; smp_wmb(); spin_lock(&c->space_lock); c->budg_idx_growth -= req->idx_growth; c->budg_uncommitted_idx += req->idx_growth; c->budg_data_growth -= req->data_growth; c->budg_dd_growth -= req->dd_growth; c->min_idx_lebs = ubifs_calc_min_idx_lebs(c); ubifs_assert(c->budg_idx_growth >= 0); ubifs_assert(c->budg_data_growth >= 0); ubifs_assert(c->budg_dd_growth >= 0); ubifs_assert(c->min_idx_lebs < c->main_lebs); ubifs_assert(!(c->budg_idx_growth & 7)); ubifs_assert(!(c->budg_data_growth & 7)); ubifs_assert(!(c->budg_dd_growth & 7)); spin_unlock(&c->space_lock); } /** * ubifs_convert_page_budget - convert budget of a new page. * @c: UBIFS file-system description object * * This function converts budget which was allocated for a new page of data to * the budget of changing an existing page of data. The latter is smaller then * the former, so this function only does simple re-calculation and does not * involve any write-back. */ void ubifs_convert_page_budget(struct ubifs_info *c) { spin_lock(&c->space_lock); /* Release the index growth reservation */ c->budg_idx_growth -= c->max_idx_node_sz << UBIFS_BLOCKS_PER_PAGE_SHIFT; /* Release the data growth reservation */ c->budg_data_growth -= c->page_budget; /* Increase the dirty data growth reservation instead */ c->budg_dd_growth += c->page_budget; /* And re-calculate the indexing space reservation */ c->min_idx_lebs = ubifs_calc_min_idx_lebs(c); spin_unlock(&c->space_lock); } /** * ubifs_release_dirty_inode_budget - release dirty inode budget. * @c: UBIFS file-system description object * @ui: UBIFS inode to release the budget for * * This function releases budget corresponding to a dirty inode. It is usually * called when after the inode has been written to the media and marked as * clean. */ void ubifs_release_dirty_inode_budget(struct ubifs_info *c, struct ubifs_inode *ui) { struct ubifs_budget_req req; memset(&req, 0, sizeof(struct ubifs_budget_req)); req.dd_growth = c->inode_budget + ALIGN(ui->data_len, 8); ubifs_release_budget(c, &req); } /** * ubifs_reported_space - calculate reported free space. * @c: the UBIFS file-system description object * @free: amount of free space * * This function calculates amount of free space which will be reported to * user-space. User-space application tend to expect that if the file-system * (e.g., via the 'statfs()' call) reports that it has N bytes available, they * are able to write a file of size N. UBIFS attaches node headers to each data * node and it has to write indexind nodes as well. This introduces additional * overhead, and UBIFS it has to report sligtly less free space to meet the * above expectetion. * * This function assumes free space is made up of uncompressed data nodes and * full index nodes (one per data node, tripled because we always allow enough * space to write the index thrice). * * Note, the calculation is pessimistic, which means that most of the time * UBIFS reports less space than it actually has. */ long long ubifs_reported_space(const struct ubifs_info *c, uint64_t free) { int divisor, factor, f; /* * Reported space size is @free * X, where X is UBIFS block size * divided by UBIFS block size + all overhead one data block * introduces. The overhead is the node header + indexing overhead. * * Indexing overhead calculations are based on the following formula: * I = N/(f - 1) + 1, where I - number of indexing nodes, N - number * of data nodes, f - fanout. Because effective UBIFS fanout is twice * as less than maximum fanout, we assume that each data node * introduces 3 * @c->max_idx_node_sz / (@c->fanout/2 - 1) bytes. * Note, the multiplier 3 is because UBIFS reseves thrice as more space * for the index. */ f = c->fanout > 3 ? c->fanout >> 1 : 2; factor = UBIFS_BLOCK_SIZE; divisor = UBIFS_MAX_DATA_NODE_SZ; divisor += (c->max_idx_node_sz * 3) / (f - 1); free *= factor; do_div(free, divisor); return free; } /** * ubifs_get_free_space - return amount of free space. * @c: UBIFS file-system description object * * This function calculates amount of free space to report to user-space. * * Because UBIFS may introduce substantial overhead (the index, node headers, * alighment, wastage at the end of eraseblocks, etc), it cannot report real * amount of free flash space it has (well, because not all dirty space is * reclamable, UBIFS does not actually know the real amount). If UBIFS did so, * it would bread user expectetion about what free space is. Users seem to * accustomed to assume that if the file-system reports N bytes of free space, * they would be able to fit a file of N bytes to the FS. This almost works for * traditional file-systems, because they have way less overhead than UBIFS. * So, to keep users happy, UBIFS tries to take the overhead into account. */ long long ubifs_get_free_space(struct ubifs_info *c) { int min_idx_lebs, rsvd_idx_lebs, lebs; long long available, outstanding, free; spin_lock(&c->space_lock); min_idx_lebs = ubifs_calc_min_idx_lebs(c); outstanding = c->budg_data_growth + c->budg_dd_growth; /* * Force the amount available to the total size reported if the used * space is zero. */ if (c->lst.total_used <= UBIFS_INO_NODE_SZ && !outstanding) { spin_unlock(&c->space_lock); return (long long)c->block_cnt << UBIFS_BLOCK_SHIFT; } available = ubifs_calc_available(c, min_idx_lebs); /* * When reporting free space to user-space, UBIFS guarantees that it is * possible to write a file of free space size. This means that for * empty LEBs we may use more precise calculations than * 'ubifs_calc_available()' is using. Namely, we know that in empty * LEBs we would waste only @c->leb_overhead bytes, not @c->dark_wm. * Thus, amend the available space. * * Note, the calculations below are similar to what we have in * 'do_budget_space()', so refer there for comments. */ if (min_idx_lebs > c->lst.idx_lebs) rsvd_idx_lebs = min_idx_lebs - c->lst.idx_lebs; else rsvd_idx_lebs = 0; lebs = c->lst.empty_lebs + c->freeable_cnt + c->idx_gc_cnt - c->lst.taken_empty_lebs; lebs -= rsvd_idx_lebs; available += lebs * (c->dark_wm - c->leb_overhead); spin_unlock(&c->space_lock); if (available > outstanding) free = ubifs_reported_space(c, available - outstanding); else free = 0; return free; }