tdb.c

samba服务器！

 /* 
   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 2 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, write to the Free Software
   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
*/

#include "tdb_private.h"

TDB_DATA tdb_null;

/*
  increment the tdb sequence number if the tdb has been opened using
  the TDB_SEQNUM flag
*/
static void tdb_increment_seqnum(struct tdb_context *tdb)
{
	tdb_off_t seqnum=0;
	
	if (!(tdb->flags & TDB_SEQNUM)) {
		return;
	}

	if (tdb_brlock(tdb, TDB_SEQNUM_OFS, F_WRLCK, F_SETLKW, 1, 1) != 0) {
		return;
	}

	/* we ignore errors from this, as we have no sane way of
	   dealing with them.
	*/
	tdb_ofs_read(tdb, TDB_SEQNUM_OFS, &seqnum);
	seqnum++;
	tdb_ofs_write(tdb, TDB_SEQNUM_OFS, &seqnum);

	tdb_brlock(tdb, TDB_SEQNUM_OFS, F_UNLCK, F_SETLKW, 1, 1);
}

static int tdb_key_compare(TDB_DATA key, TDB_DATA data, void *private_data)
{
	return memcmp(data.dptr, key.dptr, data.dsize);
}

/* Returns 0 on fail.  On success, return offset of record, and fills
   in rec */
static tdb_off_t tdb_find(struct tdb_context *tdb, TDB_DATA key, u32 hash,
			struct list_struct *r)
{
	tdb_off_t rec_ptr;
	
	/* read in the hash top */
	if (tdb_ofs_read(tdb, TDB_HASH_TOP(hash), &rec_ptr) == -1)
		return 0;

	/* keep looking until we find the right record */
	while (rec_ptr) {
		if (tdb_rec_read(tdb, rec_ptr, r) == -1)
			return 0;

		if (!TDB_DEAD(r) && hash==r->full_hash
		    && key.dsize==r->key_len
		    && tdb_parse_data(tdb, key, rec_ptr + sizeof(*r),
				      r->key_len, tdb_key_compare,
				      NULL) == 0) {
			return rec_ptr;
		}
		rec_ptr = r->next;
	}
	return TDB_ERRCODE(TDB_ERR_NOEXIST, 0);
}

/* As tdb_find, but if you succeed, keep the lock */
tdb_off_t tdb_find_lock_hash(struct tdb_context *tdb, TDB_DATA key, u32 hash, int locktype,
			   struct list_struct *rec)
{
	u32 rec_ptr;

	if (tdb_lock(tdb, BUCKET(hash), locktype) == -1)
		return 0;
	if (!(rec_ptr = tdb_find(tdb, key, hash, rec)))
		tdb_unlock(tdb, BUCKET(hash), locktype);
	return rec_ptr;
}


/* update an entry in place - this only works if the new data size
   is <= the old data size and the key exists.
   on failure return -1.
*/
static int tdb_update_hash(struct tdb_context *tdb, TDB_DATA key, u32 hash, TDB_DATA dbuf)
{
	struct list_struct rec;
	tdb_off_t rec_ptr;

	/* find entry */
	if (!(rec_ptr = tdb_find(tdb, key, hash, &rec)))
		return -1;

	/* must be long enough key, data and tailer */
	if (rec.rec_len < key.dsize + dbuf.dsize + sizeof(tdb_off_t)) {
		tdb->ecode = TDB_SUCCESS; /* Not really an error */
		return -1;
	}

	if (tdb->methods->tdb_write(tdb, rec_ptr + sizeof(rec) + rec.key_len,
		      dbuf.dptr, dbuf.dsize) == -1)
		return -1;

	if (dbuf.dsize != rec.data_len) {
		/* update size */
		rec.data_len = dbuf.dsize;
		return tdb_rec_write(tdb, rec_ptr, &rec);
	}
 
	return 0;
}

/* find an entry in the database given a key */
/* If an entry doesn't exist tdb_err will be set to
 * TDB_ERR_NOEXIST. If a key has no data attached
 * then the TDB_DATA will have zero length but
 * a non-zero pointer
 */
TDB_DATA tdb_fetch(struct tdb_context *tdb, TDB_DATA key)
{
	tdb_off_t rec_ptr;
	struct list_struct rec;
	TDB_DATA ret;
	u32 hash;

	/* find which hash bucket it is in */
	hash = tdb->hash_fn(&key);
	if (!(rec_ptr = tdb_find_lock_hash(tdb,key,hash,F_RDLCK,&rec)))
		return tdb_null;

	ret.dptr = tdb_alloc_read(tdb, rec_ptr + sizeof(rec) + rec.key_len,
				  rec.data_len);
	ret.dsize = rec.data_len;
	tdb_unlock(tdb, BUCKET(rec.full_hash), F_RDLCK);
	return ret;
}

/*
 * Find an entry in the database and hand the record's data to a parsing
 * function. The parsing function is executed under the chain read lock, so it
 * should be fast and should not block on other syscalls.
 *
 * DONT CALL OTHER TDB CALLS FROM THE PARSER, THIS MIGHT LEAD TO SEGFAULTS.
 *
 * For mmapped tdb's that do not have a transaction open it points the parsing
 * function directly at the mmap area, it avoids the malloc/memcpy in this
 * case. If a transaction is open or no mmap is available, it has to do
 * malloc/read/parse/free.
 *
 * This is interesting for all readers of potentially large data structures in
 * the tdb records, ldb indexes being one example.
 */

int tdb_parse_record(struct tdb_context *tdb, TDB_DATA key,
		     int (*parser)(TDB_DATA key, TDB_DATA data,
				   void *private_data),
		     void *private_data)
{
	tdb_off_t rec_ptr;
	struct list_struct rec;
	int ret;
	u32 hash;

	/* find which hash bucket it is in */
	hash = tdb->hash_fn(&key);

	if (!(rec_ptr = tdb_find_lock_hash(tdb,key,hash,F_RDLCK,&rec))) {
		return TDB_ERRCODE(TDB_ERR_NOEXIST, 0);
	}

	ret = tdb_parse_data(tdb, key, rec_ptr + sizeof(rec) + rec.key_len,
			     rec.data_len, parser, private_data);

	tdb_unlock(tdb, BUCKET(rec.full_hash), F_RDLCK);

	return ret;
}

/* check if an entry in the database exists 

   note that 1 is returned if the key is found and 0 is returned if not found
   this doesn't match the conventions in the rest of this module, but is
   compatible with gdbm
*/
static int tdb_exists_hash(struct tdb_context *tdb, TDB_DATA key, u32 hash)
{
	struct list_struct rec;
	
	if (tdb_find_lock_hash(tdb, key, hash, F_RDLCK, &rec) == 0)
		return 0;
	tdb_unlock(tdb, BUCKET(rec.full_hash), F_RDLCK);
	return 1;
}

int tdb_exists(struct tdb_context *tdb, TDB_DATA key)
{
	u32 hash = tdb->hash_fn(&key);
	return tdb_exists_hash(tdb, key, hash);
}

/* actually delete an entry in the database given the offset */
int tdb_do_delete(struct tdb_context *tdb, tdb_off_t rec_ptr, struct list_struct*rec)
{
	tdb_off_t last_ptr, i;
	struct list_struct lastrec;

	if (tdb->read_only || tdb->traverse_read) return -1;

	if (tdb_write_lock_record(tdb, rec_ptr) == -1) {
		/* Someone traversing here: mark it as dead */
		rec->magic = TDB_DEAD_MAGIC;
		return tdb_rec_write(tdb, rec_ptr, rec);
	}
	if (tdb_write_unlock_record(tdb, rec_ptr) != 0)
		return -1;

	/* find previous record in hash chain */
	if (tdb_ofs_read(tdb, TDB_HASH_TOP(rec->full_hash), &i) == -1)
		return -1;
	for (last_ptr = 0; i != rec_ptr; last_ptr = i, i = lastrec.next)
		if (tdb_rec_read(tdb, i, &lastrec) == -1)
			return -1;

	/* unlink it: next ptr is at start of record. */
	if (last_ptr == 0)
		last_ptr = TDB_HASH_TOP(rec->full_hash);
	if (tdb_ofs_write(tdb, last_ptr, &rec->next) == -1)
		return -1;

	/* recover the space */
	if (tdb_free(tdb, rec_ptr, rec) == -1)
		return -1;
	return 0;
}

static int tdb_count_dead(struct tdb_context *tdb, u32 hash)
{
	int res = 0;
	tdb_off_t rec_ptr;
	struct list_struct rec;
	
	/* read in the hash top */
	if (tdb_ofs_read(tdb, TDB_HASH_TOP(hash), &rec_ptr) == -1)
		return 0;

	while (rec_ptr) {
		if (tdb_rec_read(tdb, rec_ptr, &rec) == -1)
			return 0;

		if (rec.magic == TDB_DEAD_MAGIC) {
			res += 1;
		}
		rec_ptr = rec.next;
	}
	return res;
}

/*
 * Purge all DEAD records from a hash chain
 */
static int tdb_purge_dead(struct tdb_context *tdb, u32 hash)
{
	int res = -1;
	struct list_struct rec;
	tdb_off_t rec_ptr;

	if (tdb_lock(tdb, -1, F_WRLCK) == -1) {
		return -1;
	}
	
	/* read in the hash top */
	if (tdb_ofs_read(tdb, TDB_HASH_TOP(hash), &rec_ptr) == -1)
		goto fail;

	while (rec_ptr) {
		tdb_off_t next;

		if (tdb_rec_read(tdb, rec_ptr, &rec) == -1) {
			goto fail;
		}

		next = rec.next;

		if (rec.magic == TDB_DEAD_MAGIC
		    && tdb_do_delete(tdb, rec_ptr, &rec) == -1) {
			goto fail;
		}
		rec_ptr = next;
	}
	res = 0;
 fail:
	tdb_unlock(tdb, -1, F_WRLCK);
	return res;
}

/* delete an entry in the database given a key */
static int tdb_delete_hash(struct tdb_context *tdb, TDB_DATA key, u32 hash)
{
	tdb_off_t rec_ptr;
	struct list_struct rec;
	int ret;