From 23b61265b85f321ae2ceddc6c75771f8881566d8 Mon Sep 17 00:00:00 2001 From: Simo Sorce Date: Fri, 5 Sep 2008 10:13:10 -0400 Subject: Initial Import --- tdb/common/freelist.c | 382 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 382 insertions(+) create mode 100644 tdb/common/freelist.c (limited to 'tdb/common/freelist.c') diff --git a/tdb/common/freelist.c b/tdb/common/freelist.c new file mode 100644 index 00000000..2f2a4c37 --- /dev/null +++ b/tdb/common/freelist.c @@ -0,0 +1,382 @@ + /* + Unix SMB/CIFS implementation. + + trivial database library + + Copyright (C) Andrew Tridgell 1999-2005 + Copyright (C) Paul `Rusty' Russell 2000 + Copyright (C) Jeremy Allison 2000-2003 + + ** NOTE! The following LGPL license applies to the tdb + ** library. This does NOT imply that all of Samba is released + ** under the LGPL + + This library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 3 of the License, or (at your option) any later version. + + This library 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 + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with this library; if not, see . +*/ + +#include "tdb_private.h" + +/* 'right' merges can involve O(n^2) cost when combined with a + traverse, so they are disabled until we find a way to do them in + O(1) time +*/ +#define USE_RIGHT_MERGES 0 + +/* read a freelist record and check for simple errors */ +int tdb_rec_free_read(struct tdb_context *tdb, tdb_off_t off, struct list_struct *rec) +{ + if (tdb->methods->tdb_read(tdb, off, rec, sizeof(*rec),DOCONV()) == -1) + return -1; + + if (rec->magic == TDB_MAGIC) { + /* this happens when a app is showdown while deleting a record - we should + not completely fail when this happens */ + TDB_LOG((tdb, TDB_DEBUG_WARNING, "tdb_rec_free_read non-free magic 0x%x at offset=%d - fixing\n", + rec->magic, off)); + rec->magic = TDB_FREE_MAGIC; + if (tdb->methods->tdb_write(tdb, off, rec, sizeof(*rec)) == -1) + return -1; + } + + if (rec->magic != TDB_FREE_MAGIC) { + /* Ensure ecode is set for log fn. */ + tdb->ecode = TDB_ERR_CORRUPT; + TDB_LOG((tdb, TDB_DEBUG_WARNING, "tdb_rec_free_read bad magic 0x%x at offset=%d\n", + rec->magic, off)); + return TDB_ERRCODE(TDB_ERR_CORRUPT, -1); + } + if (tdb->methods->tdb_oob(tdb, rec->next+sizeof(*rec), 0) != 0) + return -1; + return 0; +} + + +#if USE_RIGHT_MERGES +/* Remove an element from the freelist. Must have alloc lock. */ +static int remove_from_freelist(struct tdb_context *tdb, tdb_off_t off, tdb_off_t next) +{ + tdb_off_t last_ptr, i; + + /* read in the freelist top */ + last_ptr = FREELIST_TOP; + while (tdb_ofs_read(tdb, last_ptr, &i) != -1 && i != 0) { + if (i == off) { + /* We've found it! */ + return tdb_ofs_write(tdb, last_ptr, &next); + } + /* Follow chain (next offset is at start of record) */ + last_ptr = i; + } + TDB_LOG((tdb, TDB_DEBUG_FATAL,"remove_from_freelist: not on list at off=%d\n", off)); + return TDB_ERRCODE(TDB_ERR_CORRUPT, -1); +} +#endif + + +/* update a record tailer (must hold allocation lock) */ +static int update_tailer(struct tdb_context *tdb, tdb_off_t offset, + const struct list_struct *rec) +{ + tdb_off_t totalsize; + + /* Offset of tailer from record header */ + totalsize = sizeof(*rec) + rec->rec_len; + return tdb_ofs_write(tdb, offset + totalsize - sizeof(tdb_off_t), + &totalsize); +} + +/* Add an element into the freelist. Merge adjacent records if + neccessary. */ +int tdb_free(struct tdb_context *tdb, tdb_off_t offset, struct list_struct *rec) +{ + /* Allocation and tailer lock */ + if (tdb_lock(tdb, -1, F_WRLCK) != 0) + return -1; + + /* set an initial tailer, so if we fail we don't leave a bogus record */ + if (update_tailer(tdb, offset, rec) != 0) { + TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_free: update_tailer failed!\n")); + goto fail; + } + +#if USE_RIGHT_MERGES + /* Look right first (I'm an Australian, dammit) */ + if (offset + sizeof(*rec) + rec->rec_len + sizeof(*rec) <= tdb->map_size) { + tdb_off_t right = offset + sizeof(*rec) + rec->rec_len; + struct list_struct r; + + if (tdb->methods->tdb_read(tdb, right, &r, sizeof(r), DOCONV()) == -1) { + TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_free: right read failed at %u\n", right)); + goto left; + } + + /* If it's free, expand to include it. */ + if (r.magic == TDB_FREE_MAGIC) { + if (remove_from_freelist(tdb, right, r.next) == -1) { + TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_free: right free failed at %u\n", right)); + goto left; + } + rec->rec_len += sizeof(r) + r.rec_len; + if (update_tailer(tdb, offset, rec) == -1) { + TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_free: update_tailer failed at %u\n", offset)); + goto fail; + } + } + } +left: +#endif + + /* Look left */ + if (offset - sizeof(tdb_off_t) > TDB_DATA_START(tdb->header.hash_size)) { + tdb_off_t left = offset - sizeof(tdb_off_t); + struct list_struct l; + tdb_off_t leftsize; + + /* Read in tailer and jump back to header */ + if (tdb_ofs_read(tdb, left, &leftsize) == -1) { + TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_free: left offset read failed at %u\n", left)); + goto update; + } + + /* it could be uninitialised data */ + if (leftsize == 0 || leftsize == TDB_PAD_U32) { + goto update; + } + + left = offset - leftsize; + + if (leftsize > offset || + left < TDB_DATA_START(tdb->header.hash_size)) { + goto update; + } + + /* Now read in the left record */ + if (tdb->methods->tdb_read(tdb, left, &l, sizeof(l), DOCONV()) == -1) { + TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_free: left read failed at %u (%u)\n", left, leftsize)); + goto update; + } + + /* If it's free, expand to include it. */ + if (l.magic == TDB_FREE_MAGIC) { + /* we now merge the new record into the left record, rather than the other + way around. This makes the operation O(1) instead of O(n). This change + prevents traverse from being O(n^2) after a lot of deletes */ + l.rec_len += sizeof(*rec) + rec->rec_len; + if (tdb_rec_write(tdb, left, &l) == -1) { + TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_free: update_left failed at %u\n", left)); + goto fail; + } + if (update_tailer(tdb, left, &l) == -1) { + TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_free: update_tailer failed at %u\n", offset)); + goto fail; + } + tdb_unlock(tdb, -1, F_WRLCK); + return 0; + } + } + +update: + + /* Now, prepend to free list */ + rec->magic = TDB_FREE_MAGIC; + + if (tdb_ofs_read(tdb, FREELIST_TOP, &rec->next) == -1 || + tdb_rec_write(tdb, offset, rec) == -1 || + tdb_ofs_write(tdb, FREELIST_TOP, &offset) == -1) { + TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_free record write failed at offset=%d\n", offset)); + goto fail; + } + + /* And we're done. */ + tdb_unlock(tdb, -1, F_WRLCK); + return 0; + + fail: + tdb_unlock(tdb, -1, F_WRLCK); + return -1; +} + + + +/* + the core of tdb_allocate - called when we have decided which + free list entry to use + + Note that we try to allocate by grabbing data from the end of an existing record, + not the beginning. This is so the left merge in a free is more likely to be + able to free up the record without fragmentation + */ +static tdb_off_t tdb_allocate_ofs(struct tdb_context *tdb, + tdb_len_t length, tdb_off_t rec_ptr, + struct list_struct *rec, tdb_off_t last_ptr) +{ +#define MIN_REC_SIZE (sizeof(struct list_struct) + sizeof(tdb_off_t) + 8) + + if (rec->rec_len < length + MIN_REC_SIZE) { + /* we have to grab the whole record */ + + /* unlink it from the previous record */ + if (tdb_ofs_write(tdb, last_ptr, &rec->next) == -1) { + return 0; + } + + /* mark it not free */ + rec->magic = TDB_MAGIC; + if (tdb_rec_write(tdb, rec_ptr, rec) == -1) { + return 0; + } + return rec_ptr; + } + + /* we're going to just shorten the existing record */ + rec->rec_len -= (length + sizeof(*rec)); + if (tdb_rec_write(tdb, rec_ptr, rec) == -1) { + return 0; + } + if (update_tailer(tdb, rec_ptr, rec) == -1) { + return 0; + } + + /* and setup the new record */ + rec_ptr += sizeof(*rec) + rec->rec_len; + + memset(rec, '\0', sizeof(*rec)); + rec->rec_len = length; + rec->magic = TDB_MAGIC; + + if (tdb_rec_write(tdb, rec_ptr, rec) == -1) { + return 0; + } + + if (update_tailer(tdb, rec_ptr, rec) == -1) { + return 0; + } + + return rec_ptr; +} + +/* allocate some space from the free list. The offset returned points + to a unconnected list_struct within the database with room for at + least length bytes of total data + + 0 is returned if the space could not be allocated + */ +tdb_off_t tdb_allocate(struct tdb_context *tdb, tdb_len_t length, struct list_struct *rec) +{ + tdb_off_t rec_ptr, last_ptr, newrec_ptr; + struct { + tdb_off_t rec_ptr, last_ptr; + tdb_len_t rec_len; + } bestfit; + float multiplier = 1.0; + + if (tdb_lock(tdb, -1, F_WRLCK) == -1) + return 0; + + /* Extra bytes required for tailer */ + length += sizeof(tdb_off_t); + length = TDB_ALIGN(length, TDB_ALIGNMENT); + + again: + last_ptr = FREELIST_TOP; + + /* read in the freelist top */ + if (tdb_ofs_read(tdb, FREELIST_TOP, &rec_ptr) == -1) + goto fail; + + bestfit.rec_ptr = 0; + bestfit.last_ptr = 0; + bestfit.rec_len = 0; + + /* + this is a best fit allocation strategy. Originally we used + a first fit strategy, but it suffered from massive fragmentation + issues when faced with a slowly increasing record size. + */ + while (rec_ptr) { + if (tdb_rec_free_read(tdb, rec_ptr, rec) == -1) { + goto fail; + } + + if (rec->rec_len >= length) { + if (bestfit.rec_ptr == 0 || + rec->rec_len < bestfit.rec_len) { + bestfit.rec_len = rec->rec_len; + bestfit.rec_ptr = rec_ptr; + bestfit.last_ptr = last_ptr; + } + } + + /* move to the next record */ + last_ptr = rec_ptr; + rec_ptr = rec->next; + + /* if we've found a record that is big enough, then + stop searching if its also not too big. The + definition of 'too big' changes as we scan + through */ + if (bestfit.rec_len > 0 && + bestfit.rec_len < length * multiplier) { + break; + } + + /* this multiplier means we only extremely rarely + search more than 50 or so records. At 50 records we + accept records up to 11 times larger than what we + want */ + multiplier *= 1.05; + } + + if (bestfit.rec_ptr != 0) { + if (tdb_rec_free_read(tdb, bestfit.rec_ptr, rec) == -1) { + goto fail; + } + + newrec_ptr = tdb_allocate_ofs(tdb, length, bestfit.rec_ptr, + rec, bestfit.last_ptr); + tdb_unlock(tdb, -1, F_WRLCK); + return newrec_ptr; + } + + /* we didn't find enough space. See if we can expand the + database and if we can then try again */ + if (tdb_expand(tdb, length + sizeof(*rec)) == 0) + goto again; + fail: + tdb_unlock(tdb, -1, F_WRLCK); + return 0; +} + + + +/* + return the size of the freelist - used to decide if we should repack +*/ +int tdb_freelist_size(struct tdb_context *tdb) +{ + tdb_off_t ptr; + int count=0; + + if (tdb_lock(tdb, -1, F_RDLCK) == -1) { + return -1; + } + + ptr = FREELIST_TOP; + while (tdb_ofs_read(tdb, ptr, &ptr) == 0 && ptr != 0) { + count++; + } + + tdb_unlock(tdb, -1, F_RDLCK); + return count; +} -- cgit