From: Volker Lendecke <vl@samba.org>
Date: Sun, 28 Oct 2018 08:06:39 +0000 (+0100)
Subject: tdb: Add tdb_traverse_chain
X-Git-Tag: tdb-1.3.17~867
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=46a87f2cbafdc84199e7e131f1d88961b37a2f78;p=thirdparty%2Fsamba.git

tdb: Add tdb_traverse_chain

This is a lightweight readonly traverse of a single chain, see the
comment in the header file.

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>
---

diff --git a/lib/tdb/common/traverse.c b/lib/tdb/common/traverse.c
index a9af1d4b824..54a69dc8d03 100644
--- a/lib/tdb/common/traverse.c
+++ b/lib/tdb/common/traverse.c
@@ -399,3 +399,113 @@ _PUBLIC_ TDB_DATA tdb_nextkey(struct tdb_context *tdb, TDB_DATA oldkey)
 	return key;
 }
 
+_PUBLIC_ int tdb_traverse_chain(struct tdb_context *tdb,
+				unsigned chain,
+				tdb_traverse_func fn,
+				void *private_data)
+{
+	tdb_off_t rec_ptr;
+	struct tdb_chainwalk_ctx chainwalk;
+	int count = 0;
+	int ret;
+
+	if (chain >= tdb->hash_size) {
+		tdb->ecode = TDB_ERR_EINVAL;
+		return -1;
+	}
+
+	if (tdb->traverse_read != 0) {
+		tdb->ecode = TDB_ERR_LOCK;
+		return -1;
+	}
+
+	ret = tdb_lock(tdb, chain, F_RDLCK);
+	if (ret == -1) {
+		return -1;
+	}
+
+	tdb->traverse_read += 1;
+
+	ret = tdb_ofs_read(tdb, TDB_HASH_TOP(chain), &rec_ptr);
+	if (ret == -1) {
+		goto fail;
+	}
+
+	tdb_chainwalk_init(&chainwalk, rec_ptr);
+
+	while (rec_ptr != 0) {
+		struct tdb_record rec;
+		bool ok;
+
+		ret = tdb_rec_read(tdb, rec_ptr, &rec);
+		if (ret == -1) {
+			goto fail;
+		}
+
+		if (!TDB_DEAD(&rec)) {
+			/* no overflow checks, tdb_rec_read checked it */
+			tdb_off_t key_ofs = rec_ptr + sizeof(rec);
+			size_t full_len = rec.key_len + rec.data_len;
+			uint8_t *buf = NULL;
+
+			TDB_DATA key = { .dsize = rec.key_len };
+			TDB_DATA data = { .dsize = rec.data_len };
+
+			if ((tdb->transaction == NULL) &&
+			    (tdb->map_ptr != NULL)) {
+				ret = tdb->methods->tdb_oob(
+					tdb, key_ofs, full_len, 0);
+				if (ret == -1) {
+					goto fail;
+				}
+				key.dptr = (uint8_t *)tdb->map_ptr + key_ofs;
+			} else {
+				buf = tdb_alloc_read(tdb, key_ofs, full_len);
+				if (buf == NULL) {
+					goto fail;
+				}
+				key.dptr = buf;
+			}
+			data.dptr = key.dptr + key.dsize;
+
+			ret = fn(tdb, key, data, private_data);
+			free(buf);
+
+			count += 1;
+
+			if (ret != 0) {
+				break;
+			}
+		}
+
+		rec_ptr = rec.next;
+
+		ok = tdb_chainwalk_check(tdb, &chainwalk, rec_ptr);
+		if (!ok) {
+			goto fail;
+		}
+	}
+	tdb->traverse_read -= 1;
+	tdb_unlock(tdb, chain, F_RDLCK);
+	return count;
+
+fail:
+	tdb->traverse_read -= 1;
+	tdb_unlock(tdb, chain, F_RDLCK);
+	return -1;
+}
+
+_PUBLIC_ int tdb_traverse_key_chain(struct tdb_context *tdb,
+				    TDB_DATA key,
+				    tdb_traverse_func fn,
+				    void *private_data)
+{
+	uint32_t hash, chain;
+	int ret;
+
+	hash = tdb->hash_fn(&key);
+	chain = BUCKET(hash);
+	ret = tdb_traverse_chain(tdb, chain, fn, private_data);
+
+	return ret;
+}
diff --git a/lib/tdb/include/tdb.h b/lib/tdb/include/tdb.h
index 535f07ac00a..445f48c1fd9 100644
--- a/lib/tdb/include/tdb.h
+++ b/lib/tdb/include/tdb.h
@@ -480,6 +480,73 @@ int tdb_traverse(struct tdb_context *tdb, tdb_traverse_func fn, void *private_da
  */
 int tdb_traverse_read(struct tdb_context *tdb, tdb_traverse_func fn, void *private_data);
 
+/**
+ * @brief Traverse a single hash chain
+ *
+ * Traverse a single hash chain under a single lock operation. No
+ * database modification is possible in the callback.
+ *
+ * This exists for background cleanup of databases. In normal
+ * operations, traversing a complete database can be much too
+ * expensive. Databases can have many chains, which will all have to
+ * be looked at before tdb_traverse finishes. Also tdb_traverse does a
+ * lot of fcntl activity to protect against concurrent record deletes.
+ *
+ * With this you can walk a fraction of the whole tdb, collect the
+ * entries you want to prune, leave the traverse, and then modify or
+ * delete the records in a subsequent step.
+ *
+ * To walk the entire database, call this function tdb_hash_size()
+ * times, with 0<=chain<tdb_hash_size(tdb).
+ *
+ * @param[in]  tdb      The database to traverse.
+ *
+ * @param[in]  chain    The hash chain number to traverse.
+ *
+ * @param[in]  fn       The function to call on each entry.
+ *
+ * @param[in]  private_data The private data which should be passed to the
+ *                          traversing function.
+ *
+ * @return              The record count traversed, -1 on error.
+ */
+
+int tdb_traverse_chain(struct tdb_context *tdb,
+		       unsigned chain,
+		       tdb_traverse_func fn,
+		       void *private_data);
+
+/**
+ * @brief Traverse a single hash chain
+ *
+ * This is like tdb_traverse_chain(), but for all records that are in
+ * the same chain as the record corresponding to the key parameter.
+ *
+ * Use it for ongoing database maintenance under a lock. Whenever you
+ * are about to modify a database, you know which record you are going
+ * to write to. For that tdb_store(), an exclusive chainlock is taken
+ * behind the scenes. To utilize this exclusive lock for incremental
+ * database cleanup as well, tdb_chainlock() the key you are about to
+ * modify, then tdb_traverse_key_chain() to do the incremental
+ * maintenance, modify your record and tdb_chainunlock() the key
+ * again.
+ *
+ * @param[in]  tdb      The database to traverse.
+ *
+ * @param[in]  key      The record key to walk the chain for.
+ *
+ * @param[in]  fn       The function to call on each entry.
+ *
+ * @param[in]  private_data The private data which should be passed to the
+ *                          traversing function.
+ *
+ * @return              The record count traversed, -1 on error.
+ */
+
+int tdb_traverse_key_chain(struct tdb_context *tdb,
+			   TDB_DATA key,
+			   tdb_traverse_func fn,
+			   void *private_data);
 /**
  * @brief Check if an entry in the database exists.
  *