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samba-mirror/source3/lib/tdb/common/freelist.c

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/*
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 <http://www.gnu.org/licenses/>.
*/
#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
*/
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)
{
struct list_struct newrec;
tdb_off_t newrec_ptr;
memset(&newrec, '\0', sizeof(newrec));
/* found it - now possibly split it up */
if (rec->rec_len > length + MIN_REC_SIZE) {
/* Length of left piece */
length = TDB_ALIGN(length, TDB_ALIGNMENT);
/* Right piece to go on free list */
newrec.rec_len = rec->rec_len - (sizeof(*rec) + length);
newrec_ptr = rec_ptr + sizeof(*rec) + length;
/* And left record is shortened */
rec->rec_len = length;
} else {
newrec_ptr = 0;
}
/* Remove allocated record from the free list */
if (tdb_ofs_write(tdb, last_ptr, &rec->next) == -1) {
return 0;
}
/* Update header: do this before we drop alloc
lock, otherwise tdb_free() might try to
merge with us, thinking we're free.
(Thanks Jeremy Allison). */
rec->magic = TDB_MAGIC;
if (tdb_rec_write(tdb, rec_ptr, rec) == -1) {
return 0;
}
/* Did we create new block? */
if (newrec_ptr) {
/* Update allocated record tailer (we
shortened it). */
if (update_tailer(tdb, rec_ptr, rec) == -1) {
return 0;
}
/* Free new record */
if (tdb_free(tdb, newrec_ptr, &newrec) == -1) {
return 0;
}
}
/* all done - return the new record offset */
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);
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;
}