tdb.c

经典的ppp程序

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

 out:
	tdb_unlock(tdb, BUCKET(hash));
	return ret;
}

/* find an entry in the database given a key */
TDB_DATA tdb_fetch(TDB_CONTEXT *tdb, TDB_DATA key)
{
	unsigned hash;
	tdb_off rec_ptr;
	struct list_struct rec;
	TDB_DATA ret = null_data;

        if (tdb == NULL) {
#ifdef TDB_DEBUG
            printf("tdb_fetch() called with null context\n");
#endif
            return null_data;
        }

	/* find which hash bucket it is in */
	hash = tdb_hash(&key);

	tdb_lock(tdb, BUCKET(hash));
	rec_ptr = tdb_find(tdb, key, hash, &rec);

	if (rec_ptr) {
		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(hash));
	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
*/
int tdb_exists(TDB_CONTEXT *tdb, TDB_DATA key)
{
	unsigned hash;
	tdb_off rec_ptr;
	struct list_struct rec;
	
        if (tdb == NULL) {
#ifdef TDB_DEBUG
            printf("tdb_exists() called with null context\n");
#endif
            return 0;
        }

	/* find which hash bucket it is in */
	hash = tdb_hash(&key);

	tdb_lock(tdb, BUCKET(hash));
	rec_ptr = tdb_find(tdb, key, hash, &rec);
	tdb_unlock(tdb, BUCKET(hash));

	return rec_ptr != 0;
}

/* 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, int (*fn)(TDB_CONTEXT *tdb, TDB_DATA key, TDB_DATA dbuf, void* state), void* state)
{
	int count = 0;
	unsigned h;
	tdb_off offset, rec_ptr;
	struct list_struct rec;
	char *data;
	TDB_DATA key, dbuf;

        if (tdb == NULL) {
#ifdef TDB_DEBUG
            printf("tdb_traverse() called with null context\n");
#endif
            return -1;
        }

	/* loop over all hash chains */
	for (h = 0; h < tdb->header.hash_size; h++) {
		tdb_lock(tdb, BUCKET(h));

		/* read in the hash top */
		offset = tdb_hash_top(tdb, h);
		if (ofs_read(tdb, offset, &rec_ptr) == -1) {
			goto fail;
		}

		/* traverse all records for this hash */
		while (rec_ptr) {
			if (rec_read(tdb, rec_ptr, &rec) == -1) {
				goto fail;
			}

			/* now read the full record */
			data = tdb_alloc_read(tdb, rec_ptr + sizeof(rec), 
					     rec.key_len + rec.data_len);
			if (!data) {
				goto fail;
			}

			key.dptr = data;
			key.dsize = rec.key_len;
			dbuf.dptr = data + rec.key_len;
			dbuf.dsize = rec.data_len;
			count++;

			if (fn && fn(tdb, key, dbuf, state) != 0) {
				/* they want us to stop traversing */
				free(data);
				tdb_unlock(tdb, BUCKET(h));
				return count;
			}

			/* a miss - drat */
			free(data);

			/* move to the next record */
			rec_ptr = rec.next;
		}
		tdb_unlock(tdb, BUCKET(h));
	}

	/* return the number traversed */
	return count;

 fail:
	tdb_unlock(tdb, BUCKET(h));
	return -1;
}


/* find the first entry in the database and return its key */
TDB_DATA tdb_firstkey(TDB_CONTEXT *tdb)
{
	tdb_off offset, rec_ptr;
	struct list_struct rec;
	unsigned hash;
	TDB_DATA ret;

        if (tdb == NULL) {
#ifdef TDB_DEBUG
            printf("tdb_firstkey() called with null context\n");
#endif
            return null_data;
        }

	/* look for a non-empty hash chain */
	for (hash = 0, rec_ptr = 0; 
	     hash < tdb->header.hash_size;
	     hash++) {
		/* find the top of the hash chain */
		offset = tdb_hash_top(tdb, hash);

		tdb_lock(tdb, BUCKET(hash));

		/* read in the hash top */
		if (ofs_read(tdb, offset, &rec_ptr) == -1) {
			goto fail;
		}

		if (rec_ptr) break;

		tdb_unlock(tdb, BUCKET(hash));
	}

	if (rec_ptr == 0) return null_data;

	/* we've found a non-empty chain, now read the record */
	if (rec_read(tdb, rec_ptr, &rec) == -1) {
		goto fail;
	}

	/* allocate and read the key space */
	ret.dptr = tdb_alloc_read(tdb, rec_ptr + sizeof(rec), rec.key_len);
	ret.dsize = rec.key_len;
	tdb_unlock(tdb, BUCKET(hash));
	return ret;

 fail:
	tdb_unlock(tdb, BUCKET(hash));
	return null_data;
}

/* find the next entry in the database, returning its key */
TDB_DATA tdb_nextkey(TDB_CONTEXT *tdb, TDB_DATA key)
{
	unsigned hash, hbucket;
	tdb_off rec_ptr, offset;
	struct list_struct rec;
	TDB_DATA ret;

        if (tdb == NULL) {
#ifdef TDB_DEBUG
            printf("tdb_nextkey() called with null context\n");
#endif
            return null_data;
        }

	/* find which hash bucket it is in */
	hash = tdb_hash(&key);
	hbucket = BUCKET(hash);
	
	tdb_lock(tdb, hbucket);
	rec_ptr = tdb_find(tdb, key, hash, &rec);
	if (rec_ptr) {
		/* we want the next record after this one */
		rec_ptr = rec.next;
	}

	/* not found or last in hash: look for next non-empty hash chain */
	while (rec_ptr == 0) {
		tdb_unlock(tdb, hbucket);

		if (++hbucket >= tdb->header.hash_size - 1)
			return null_data;

		offset = tdb_hash_top(tdb, hbucket);
		tdb_lock(tdb, hbucket);
		/* read in the hash top */
		if (ofs_read(tdb, offset, &rec_ptr) == -1) {
			tdb_unlock(tdb, hbucket);
			return null_data;
		}
	}

	/* Read the record. */
	if (rec_read(tdb, rec_ptr, &rec) == -1) {
		tdb_unlock(tdb, hbucket);
		return null_data;
	}
	/* allocate and read the key */
	ret.dptr = tdb_alloc_read(tdb, rec_ptr + sizeof(rec), rec.key_len);
	ret.dsize = rec.key_len;
	tdb_unlock(tdb, hbucket);

	return ret;
}

/* delete an entry in the database given a key */
int tdb_delete(TDB_CONTEXT *tdb, TDB_DATA key)
{
	unsigned hash;
	tdb_off offset, rec_ptr, last_ptr;
	struct list_struct rec, lastrec;
	char *data = NULL;

        if (tdb == NULL) {
#ifdef TDB_DEBUG
            printf("tdb_delete() called with null context\n");
#endif
            return -1;
        }

	/* find which hash bucket it is in */
	hash = tdb_hash(&key);

	tdb_lock(tdb, BUCKET(hash));

	/* find the top of the hash chain */
	offset = tdb_hash_top(tdb, hash);

	/* read in the hash top */
	if (ofs_read(tdb, offset, &rec_ptr) == -1) {
		goto fail;
	}

	last_ptr = 0;

	/* keep looking until we find the right record */
	while (rec_ptr) {
		if (rec_read(tdb, rec_ptr, &rec) == -1) {
			goto fail;
		}

		if (hash == rec.full_hash && key.dsize == rec.key_len) {
			/* a very likely hit - read the record and full key */
			data = tdb_alloc_read(tdb, rec_ptr + sizeof(rec), 
					     rec.key_len);
			if (!data) {
				goto fail;
			}

			if (memcmp(key.dptr, data, key.dsize) == 0) {
				/* a definite match - delete it */
				if (last_ptr == 0) {
					offset = tdb_hash_top(tdb, hash);
					if (ofs_write(tdb, offset, &rec.next) == -1) {
						goto fail;
					}
				} else {
					lastrec.next = rec.next;
					if (rec_write(tdb, last_ptr, &lastrec) == -1) {
						goto fail;
					}					
				}
				tdb_unlock(tdb, BUCKET(hash));
				tdb_lock(tdb, -1);
				/* and recover the space */
				offset = FREELIST_TOP;
				if (ofs_read(tdb, offset, &rec.next) == -1) {
					goto fail2;
				}
				rec.magic = TDB_FREE_MAGIC;
				if (rec_write(tdb, rec_ptr, &rec) == -1) {
					goto fail2;
				}
				if (ofs_write(tdb, offset, &rec_ptr) == -1) {
					goto fail2;
				}

				/* yipee - all done */
				free(data);
				tdb_unlock(tdb, -1);
				return 0;
			}

			/* a miss - drat */
			free(data);
			data = NULL;
		}

		/* move to the next record */
		last_ptr = rec_ptr;
		lastrec = rec;
		rec_ptr = rec.next;
	}

 fail:
	if (data) free(data);
	tdb_unlock(tdb, BUCKET(hash));
	return -1;

 fail2:
	if (data) free(data);
	tdb_unlock(tdb, -1);
	return -1;
}


/* 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;
	unsigned hash;
	tdb_off rec_ptr, offset;
	char *p = NULL;

        if (tdb == NULL) {
#ifdef TDB_DEBUG
            printf("tdb_store() called with null context\n");
#endif
            return -1;
        }

	/* find which hash bucket it is in */
	hash = tdb_hash(&key);

	/* check for it existing */
	if (flag == TDB_INSERT && tdb_exists(tdb, key)) {
		tdb->ecode = TDB_ERR_EXISTS;
		return -1;
	}

	/* first try in-place update */
	if (flag != TDB_INSERT && tdb_update(tdb, key, dbuf) == 0) {
		return 0;
	}

	rec_ptr = tdb_allocate(tdb, key.dsize + dbuf.dsize);
	if (rec_ptr == 0) {
		return -1;
	}

	tdb_lock(tdb, BUCKET(hash));

	/* delete any existing record - if it doesn't exist we don't care */
	if (flag != TDB_INSERT) {
		tdb_delete(tdb, key);
	}

	/* read the newly created record */
	if (tdb_read(tdb, rec_ptr, (char *)&rec, sizeof(rec)) == -1) {
		goto fail;
	}

	if (rec.magic != TDB_FREE_MAGIC) goto fail;

	/* find the top of the hash chain */
	offset = tdb_hash_top(tdb, hash);

	/* read in the hash top diretcly into our next pointer */
	if (ofs_read(tdb, offset, &rec.next) == -1) {
		goto fail;
	}

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

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

	memcpy(p, &rec, sizeof(rec));
	memcpy(p+sizeof(rec), key.dptr, key.dsize);
	memcpy(p+sizeof(rec)+key.dsize, dbuf.dptr, dbuf.dsize);

	if (tdb_write(tdb, rec_ptr, p, sizeof(rec)+key.dsize+dbuf.dsize) == -1)
		goto fail;

	free(p); 
	p = NULL;

	/* and point the top of the hash chain at it */
	if (ofs_write(tdb, offset, &rec_ptr) == -1) goto fail;

	tdb_unlock(tdb, BUCKET(hash));
	return 0;

 fail:
#if TDB_DEBUG
	printf("store failed for hash 0x%08x in bucket %u\n", hash, BUCKET(hash));
#endif
	if (p) free(p);
	tdb_unlock(tdb, BUCKET(hash));
	return -1;
}


/* open the database, creating it if necessary 

   The open_flags and mode are passed straight to the open call on the database
   file. A flags value of O_WRONLY is invalid

   The hash size is advisory, use zero for a default value. 

   return is NULL on error
*/
TDB_CONTEXT *tdb_open(char *name, int hash_size, int tdb_flags,
		      int open_flags, mode_t mode)
{
	TDB_CONTEXT tdb, *ret;
	struct stat st;

	memset(&tdb, 0, sizeof(tdb));

	tdb.fd = -1;
	tdb.name = NULL;
	tdb.map_ptr = NULL;

	if ((open_flags & O_ACCMODE) == O_WRONLY) {
		goto fail;
	}

	if (hash_size == 0) hash_size = DEFAULT_HASH_SIZE;

	tdb.read_only = ((open_flags & O_ACCMODE) == O_RDONLY);

        if (name != NULL) {
            tdb.fd = open(name, open_flags, mode);
            if (tdb.fd == -1) {
		goto fail;
            }
        }

	/* ensure there is only one process initialising at once */
	tdb_brlock(&tdb, GLOBAL_LOCK, LOCK_SET, F_WRLCK, F_SETLKW);
	
	if (tdb_flags & TDB_CLEAR_IF_FIRST) {
		/* we need to zero the database if we are the only
		   one with it open */
		if (tdb_brlock(&tdb, ACTIVE_LOCK, LOCK_SET, F_WRLCK, F_SETLK) == 0) {
			ftruncate(tdb.fd, 0);
			tdb_brlock(&tdb, ACTIVE_LOCK, LOCK_CLEAR, F_WRLCK, F_SETLK);
		}
	}

	/* leave this lock in place */
	tdb_brlock(&tdb, ACTIVE_LOCK, LOCK_SET, F_RDLCK, F_SETLKW);

	if (read(tdb.fd, &tdb.header, sizeof(tdb.header)) != sizeof(tdb.header) ||
	    strcmp(tdb.header.magic_food, TDB_MAGIC_FOOD) != 0 ||
	    tdb.header.version != TDB_VERSION) {
		/* its not a valid database - possibly initialise it */
		if (!(open_flags & O_CREAT)) {
			goto fail;
		}
		if (tdb_new_database(&tdb, hash_size) == -1) goto fail;

		lseek(tdb.fd, 0, SEEK_SET);
		if (tdb.fd != -1 && read(tdb.fd, &tdb.header, 
                                         sizeof(tdb.header)) != 
                                         sizeof(tdb.header)) 
                    goto fail;
	}

        if (tdb.fd != -1) {
            fstat(tdb.fd, &st);

            /* map the database and fill in the return structure */
            tdb.name = (char *)strdup(name);
            tdb.map_size = st.st_size;
        }

        tdb.locked = (int *)calloc(tdb.header.hash_size+1, 
                                   sizeof(tdb.locked[0]));
        if (!tdb.locked) {
            goto fail;
        }

#if HAVE_MMAP
        if (tdb.fd != -1) {
            tdb.map_ptr = (void *)mmap(NULL, st.st_size, 
                                       tdb.read_only? PROT_READ : PROT_READ|PROT_WRITE,
                                       MAP_SHARED | MAP_FILE, tdb.fd, 0);
        }
#endif

	ret = (TDB_CONTEXT *)malloc(sizeof(tdb));
	if (!ret) goto fail;

	*ret = tdb;

#if TDB_DEBUG
	printf("mapped database of hash_size %u map_size=%u\n", 
	       hash_size, tdb.map_size);
#endif

	tdb_brlock(&tdb, GLOBAL_LOCK, LOCK_CLEAR, F_WRLCK, F_SETLKW);
	return ret;

 fail:
        if (tdb.name) free(tdb.name);
	if (tdb.fd != -1) close(tdb.fd);
	if (tdb.map_ptr) munmap(tdb.map_ptr, tdb.map_size);

	return NULL;
}

/* close a database */
int tdb_close(TDB_CONTEXT *tdb)
{
	if (!tdb) return -1;

	if (tdb->name) free(tdb->name);
	if (tdb->fd != -1) close(tdb->fd);
	if (tdb->locked) free(tdb->locked);

	if (tdb->map_ptr) {
            if (tdb->fd != -1) {
                munmap(tdb->map_ptr, tdb->map_size);
            } else {
                free(tdb->map_ptr);
            }
        }

	memset(tdb, 0, sizeof(*tdb));
	free(tdb);

	return 0;
}

/* lock the database. If we already have it locked then don't do anything */
int tdb_writelock(TDB_CONTEXT *tdb)
{
        if (tdb == NULL) {
#ifdef TDB_DEBUG
            printf("tdb_writelock() called with null context\n");
#endif
            return -1;
        }

	return tdb_lock(tdb, -1);
}

/* unlock the database. */
int tdb_writeunlock(TDB_CONTEXT *tdb)
{
        if (tdb == NULL) {
#ifdef TDB_DEBUG
            printf("tdb_writeunlock() called with null context\n");
#endif
            return -1;
        }

	return tdb_unlock(tdb, -1);
}

/* lock one hash chain. This is meant to be used to reduce locking
   contention - it cannot guarantee how many records will be locked */
int tdb_lockchain(TDB_CONTEXT *tdb, TDB_DATA key)
{
        if (tdb == NULL) {
#ifdef TDB_DEBUG
            printf("tdb_lockchain() called with null context\n");
#endif
            return -1;
        }

	return tdb_lock(tdb, BUCKET(tdb_hash(&key)));
}


/* unlock one hash chain */
int tdb_unlockchain(TDB_CONTEXT *tdb, TDB_DATA key)
{
        if (tdb == NULL) {
#ifdef TDB_DEBUG
            printf("tdb_unlockchain() called with null context\n");
#endif
            return -1;
        }

	return tdb_unlock(tdb, BUCKET(tdb_hash(&key)));
}