tdb.c

自己精简过的PPPD代码。在嵌入中应用可以更好的发挥。比原先的小了很多

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

enum TDB_ERROR tdb_error(TDB_CONTEXT *tdb)
{
	return tdb->ecode;
}

static struct tdb_errname {
	enum TDB_ERROR ecode; const char *estring;
} emap[] = { {TDB_SUCCESS, "Success"},
	     {TDB_ERR_CORRUPT, "Corrupt database"},
	     {TDB_ERR_IO, "IO Error"},
	     {TDB_ERR_LOCK, "Locking error"},
	     {TDB_ERR_OOM, "Out of memory"},
	     {TDB_ERR_EXISTS, "Record exists"},
	     {TDB_ERR_NOLOCK, "Lock exists on other keys"},
	     {TDB_ERR_NOEXIST, "Record does not exist"} };

/* Error string for the last tdb error */
const char *tdb_errorstr(TDB_CONTEXT *tdb)
{
	u32 i;
	for (i = 0; i < sizeof(emap) / sizeof(struct tdb_errname); i++)
		if (tdb->ecode == emap[i].ecode)
			return emap[i].estring;
	return "Invalid error code";
}

/* 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(TDB_CONTEXT *tdb, TDB_DATA key, u32 hash, TDB_DATA dbuf)
{
	struct list_struct rec;
	tdb_off 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)) {
		tdb->ecode = TDB_SUCCESS; /* Not really an error */
		return -1;
	}

	if (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 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
 * tdb_err will not be set. Both will return a
 * zero pptr and zero dsize.
 */

TDB_DATA tdb_fetch(TDB_CONTEXT *tdb, TDB_DATA key)
{
	tdb_off 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;

	if (rec.data_len)
		ret.dptr = tdb_alloc_read(tdb, rec_ptr + sizeof(rec) + rec.key_len,
					  rec.data_len);
	else
		ret.dptr = NULL;
	ret.dsize = rec.data_len;
	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(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(TDB_CONTEXT *tdb, TDB_DATA key)
{
	u32 hash = tdb->hash_fn(&key);
	return tdb_exists_hash(tdb, key, hash);
}

/* record lock stops delete underneath */
static int lock_record(TDB_CONTEXT *tdb, tdb_off off)
{
	return off ? tdb_brlock(tdb, off, F_RDLCK, F_SETLKW, 0) : 0;
}
/*
  Write locks override our own fcntl readlocks, so check it here.
  Note this is meant to be F_SETLK, *not* F_SETLKW, as it's not
  an error to fail to get the lock here.
*/
 
static int write_lock_record(TDB_CONTEXT *tdb, tdb_off off)
{
	struct tdb_traverse_lock *i;
	for (i = &tdb->travlocks; i; i = i->next)
		if (i->off == off)
			return -1;
	return tdb_brlock(tdb, off, F_WRLCK, F_SETLK, 1);
}

/*
  Note this is meant to be F_SETLK, *not* F_SETLKW, as it's not
  an error to fail to get the lock here.
*/

static int write_unlock_record(TDB_CONTEXT *tdb, tdb_off off)
{
	return tdb_brlock(tdb, off, F_UNLCK, F_SETLK, 0);
}
/* fcntl locks don't stack: avoid unlocking someone else's */
static int unlock_record(TDB_CONTEXT *tdb, tdb_off off)
{
	struct tdb_traverse_lock *i;
	u32 count = 0;

	if (off == 0)
		return 0;
	for (i = &tdb->travlocks; i; i = i->next)
		if (i->off == off)
			count++;
	return (count == 1 ? tdb_brlock(tdb, off, F_UNLCK, F_SETLKW, 0) : 0);
}

/* actually delete an entry in the database given the offset */
static int do_delete(TDB_CONTEXT *tdb, tdb_off rec_ptr, struct list_struct*rec)
{
	tdb_off last_ptr, i;
	struct list_struct lastrec;

	if (tdb->read_only) return -1;

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

	/* find previous record in hash chain */
	if (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 (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 (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;
}

/* Uses traverse lock: 0 = finish, -1 = error, other = record offset */
static int tdb_next_lock(TDB_CONTEXT *tdb, struct tdb_traverse_lock *tlock,
			 struct list_struct *rec)
{
	int want_next = (tlock->off != 0);

	/* Lock each chain from the start one. */
	for (; tlock->hash < tdb->header.hash_size; tlock->hash++) {
		if (tdb_lock(tdb, tlock->hash, F_WRLCK) == -1)
			return -1;

		/* No previous record?  Start at top of chain. */
		if (!tlock->off) {
			if (ofs_read(tdb, TDB_HASH_TOP(tlock->hash),
				     &tlock->off) == -1)
				goto fail;
		} else {
			/* Otherwise unlock the previous record. */
			if (unlock_record(tdb, tlock->off) != 0)
				goto fail;
		}

		if (want_next) {
			/* We have offset of old record: grab next */
			if (rec_read(tdb, tlock->off, rec) == -1)
				goto fail;
			tlock->off = rec->next;
		}

		/* Iterate through chain */
		while( tlock->off) {
			tdb_off current;
			if (rec_read(tdb, tlock->off, rec) == -1)
				goto fail;
			if (!TDB_DEAD(rec)) {
				/* Woohoo: we found one! */
				if (lock_record(tdb, tlock->off) != 0)
					goto fail;
				return tlock->off;
			}
			/* Try to clean dead ones from old traverses */
			current = tlock->off;
			tlock->off = rec->next;
			if (!tdb->read_only && 
			    do_delete(tdb, current, rec) != 0)
				goto fail;
		}
		tdb_unlock(tdb, tlock->hash, F_WRLCK);
		want_next = 0;
	}
	/* We finished iteration without finding anything */
	return TDB_ERRCODE(TDB_SUCCESS, 0);

 fail:
	tlock->off = 0;
	if (tdb_unlock(tdb, tlock->hash, F_WRLCK) != 0)
		TDB_LOG((tdb, 0, "tdb_next_lock: On error unlock failed!\n"));
	return -1;
}

/* traverse the entire database - calling fn(tdb, key, data) on each element.
   return -1 on error or the record count traversed
   if fn is NULL then it is not called
   a non-zero return value from fn() indicates that the traversal should stop
  */
int tdb_traverse(TDB_CONTEXT *tdb, tdb_traverse_func fn, void *private)
{
	TDB_DATA key, dbuf;
	struct list_struct rec;
	struct tdb_traverse_lock tl = { NULL, 0, 0 };
	int ret, count = 0;

	/* This was in the initializaton, above, but the IRIX compiler
	 * did not like it.  crh
	 */
	tl.next = tdb->travlocks.next;

	/* fcntl locks don't stack: beware traverse inside traverse */
	tdb->travlocks.next = &tl;

	/* tdb_next_lock places locks on the record returned, and its chain */
	while ((ret = tdb_next_lock(tdb, &tl, &rec)) > 0) {
		count++;
		/* now read the full record */
		key.dptr = tdb_alloc_read(tdb, tl.off + sizeof(rec), 
					  rec.key_len + rec.data_len);
		if (!key.dptr) {
			ret = -1;
			if (tdb_unlock(tdb, tl.hash, F_WRLCK) != 0)
				goto out;
			if (unlock_record(tdb, tl.off) != 0)
				TDB_LOG((tdb, 0, "tdb_traverse: key.dptr == NULL and unlock_record failed!\n"));
			goto out;
		}
		key.dsize = rec.key_len;
		dbuf.dptr = key.dptr + rec.key_len;
		dbuf.dsize = rec.data_len;

		/* Drop chain lock, call out */
		if (tdb_unlock(tdb, tl.hash, F_WRLCK) != 0) {
			ret = -1;
			goto out;
		}
		if (fn && fn(tdb, key, dbuf, private)) {
			/* They want us to terminate traversal */
			ret = count;
			if (unlock_record(tdb, tl.off) != 0) {
				TDB_LOG((tdb, 0, "tdb_traverse: unlock_record failed!\n"));;
				ret = -1;
			}
			tdb->travlocks.next = tl.next;
			SAFE_FREE(key.dptr);
			return count;
		}
		SAFE_FREE(key.dptr);
	}
out:
	tdb->travlocks.next = tl.next;
	if (ret < 0)
		return -1;
	else
		return count;
}

/* find the first entry in the database and return its key */
TDB_DATA tdb_firstkey(TDB_CONTEXT *tdb)
{
	TDB_DATA key;
	struct list_struct rec;

	/* release any old lock */
	if (unlock_record(tdb, tdb->travlocks.off) != 0)
		return tdb_null;
	tdb->travlocks.off = tdb->travlocks.hash = 0;

	if (tdb_next_lock(tdb, &tdb->travlocks, &rec) <= 0)
		return tdb_null;
	/* now read the key */
	key.dsize = rec.key_len;
	key.dptr =tdb_alloc_read(tdb,tdb->travlocks.off+sizeof(rec),key.dsize);
	if (tdb_unlock(tdb, BUCKET(tdb->travlocks.hash), F_WRLCK) != 0)
		TDB_LOG((tdb, 0, "tdb_firstkey: error occurred while tdb_unlocking!\n"));
	return key;
}

/* find the next entry in the database, returning its key */
TDB_DATA tdb_nextkey(TDB_CONTEXT *tdb, TDB_DATA oldkey)
{
	u32 oldhash;
	TDB_DATA key = tdb_null;
	struct list_struct rec;
	char *k = NULL;

	/* Is locked key the old key?  If so, traverse will be reliable. */
	if (tdb->travlocks.off) {
		if (tdb_lock(tdb,tdb->travlocks.hash,F_WRLCK))
			return tdb_null;
		if (rec_read(tdb, tdb->travlocks.off, &rec) == -1
		    || !(k = tdb_alloc_read(tdb,tdb->travlocks.off+sizeof(rec),
					    rec.key_len))
		    || memcmp(k, oldkey.dptr, oldkey.dsize) != 0) {
			/* No, it wasn't: unlock it and start from scratch */
			if (unlock_record(tdb, tdb->travlocks.off) != 0)
				return tdb_null;
			if (tdb_unlock(tdb, tdb->travlocks.hash, F_WRLCK) != 0)
				return tdb_null;
			tdb->travlocks.off = 0;
		}

		SAFE_FREE(k);
	}

	if (!tdb->travlocks.off) {
		/* No previous element: do normal find, and lock record */
		tdb->travlocks.off = tdb_find_lock_hash(tdb, oldkey, tdb->hash_fn(&oldkey), F_WRLCK, &rec);
		if (!tdb->travlocks.off)
			return tdb_null;
		tdb->travlocks.hash = BUCKET(rec.full_hash);
		if (lock_record(tdb, tdb->travlocks.off) != 0) {
			TDB_LOG((tdb, 0, "tdb_nextkey: lock_record failed (%s)!\n", strerror(errno)));
			return tdb_null;
		}
	}
	oldhash = tdb->travlocks.hash;

	/* Grab next record: locks chain and returned record,
	   unlocks old record */
	if (tdb_next_lock(tdb, &tdb->travlocks, &rec) > 0) {
		key.dsize = rec.key_len;
		key.dptr = tdb_alloc_read(tdb, tdb->travlocks.off+sizeof(rec),
					  key.dsize);
		/* Unlock the chain of this new record */
		if (tdb_unlock(tdb, tdb->travlocks.hash, F_WRLCK) != 0)
			TDB_LOG((tdb, 0, "tdb_nextkey: WARNING tdb_unlock failed!\n"));
	}
	/* Unlock the chain of old record */
	if (tdb_unlock(tdb, BUCKET(oldhash), F_WRLCK) != 0)
		TDB_LOG((tdb, 0, "tdb_nextkey: WARNING tdb_unlock failed!\n"));
	return key;
}

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

	if (!(rec_ptr = tdb_find_lock_hash(tdb, key, hash, F_WRLCK, &rec)))
		return -1;
	ret = do_delete(tdb, rec_ptr, &rec);
	if (tdb_unlock(tdb, BUCKET(rec.full_hash), F_WRLCK) != 0)
		TDB_LOG((tdb, 0, "tdb_delete: WARNING tdb_unlock failed!\n"));
	return ret;
}

int tdb_delete(TDB_CONTEXT *tdb, TDB_DATA key)
{
	u32 hash = tdb->hash_fn(&key);
	return tdb_delete_hash(tdb, key, hash);
}

/* store an element in the database, replacing any existing element
   with the same key 

   return 0 on success, -1 on failure
*/
int tdb_store(TDB_CONTEXT *tdb, TDB_DATA key, TDB_DATA dbuf, int flag)
{
	struct list_struct rec;
	u32 hash;
	tdb_off rec_ptr;
	char *p = NULL;
	int ret = 0;

	/* find which hash bucket it is in */
	hash = tdb->hash_fn(&key);
	if (tdb_lock(tdb, BUCKET(hash), F_WRLCK) == -1)
		return -1;

	/* check for it existing, on insert. */
	if (flag == TDB_INSERT) {
		if (tdb_exists_hash(tdb, key, hash)) {
			tdb->ecode = TDB_ERR_EXISTS;
			goto fail;
		}
	} else {
		/* first try in-place update, on modify or replace. */
		if (tdb_update_hash(tdb, key, hash, dbuf) == 0)
			goto out;
		if (tdb->ecode == TDB_ERR_NOEXIST &&
		    flag == TDB_MODIFY) {
			/* if the record doesn't exist and we are in TDB_MODIFY mode then
			 we should fail the store */
			goto fail;
	}
	}
	/* reset the error code potentially set by the tdb_update() */
	tdb->ecode = TDB_SUCCESS;

	/* delete any existing record - if it doesn't exist we don't
           care.  Doing this first reduces fragmentation, and avoids
           coalescing with `allocated' block before it's updated. */
	if (flag != TDB_INSERT)
		tdb_delete_hash(tdb, key, hash);

	/* Copy key+value *before* allocating free space in case malloc
	   fails and we are left with a dead spot in the tdb. */

	if (!(p = (char *)malloc(key.dsize + dbuf.dsize))) {
		tdb->ecode = TDB_ERR_OOM;
		goto fail;
	}

	memcpy(p, key.dptr, key.dsize);
	if (dbuf.dsize)
		memcpy(p+key.dsize, dbuf.dptr, dbuf.dsize);

	/* we have to allocate some space */
	if (!(rec_ptr = tdb_allocate(tdb, key.dsize + dbuf.dsize, &rec)))
		goto fail;

	/* Read hash top into next ptr */
	if (ofs_read(tdb, TDB_HASH_TOP(hash), &rec.next) == -1)
		goto fail;

	rec.key_len = key.dsize;
	rec.data_len = dbuf.dsize;
	rec.full_hash = hash;
	rec.magic = TDB_MAGIC;

	/* write out and point the top of the hash chain at it */
	if (rec_write(tdb, rec_ptr, &rec) == -1
	    || tdb_write(tdb, rec_ptr+sizeof(rec), p, key.dsize+dbuf.dsize)==-1
	    || ofs_write(tdb, TDB_HASH_TOP(hash), &rec_ptr) == -1) {
		/* Need to tdb_unallocate() here */
		goto fail;
	}
 out:
	SAFE_FREE(p); 
	tdb_unlock(tdb, BUCKET(hash), F_WRLCK);
	return ret;
fail:
	ret = -1;
	goto out;
}

/* Attempt to append data to 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. Record must be locked before calling.