source: branches/samba-3.2.x/source/lib/dbwrap_tdb2.c

/*
   Unix SMB/CIFS implementation.

   Database interface wrapper around tdb/ctdb

   Copyright (C) Volker Lendecke 2005-2007
   Copyright (C) Stefan Metzmacher 2008

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   This program 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 General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

#include "includes.h"
#include "librpc/gen_ndr/ndr_messaging.h"

struct db_tdb2_ctx {
        struct db_context *db;
        const char *name;
        struct tdb_wrap *mtdb;
        const char *mtdb_path;
        bool master_transaction;
        struct {
                int hash_size;
                int tdb_flags;
                int open_flags;
                mode_t mode;
        } open;
        struct tdb_wrap *ltdb;
        const char *ltdb_path;
        bool local_transaction;
        int transaction;
        bool out_of_sync;
        uint32_t lseqnum;
        uint32_t mseqnum;
#define DB_TDB2_MASTER_SEQNUM_KEYSTR "DB_TDB2_MASTER_SEQNUM_KEYSTR"
        TDB_DATA mseqkey;
        uint32_t max_buffer_size;
        uint32_t current_buffer_size;
        struct dbwrap_tdb2_changes changes;
};


static NTSTATUS db_tdb2_store(struct db_record *rec, TDB_DATA data, int flag);
static NTSTATUS db_tdb2_delete(struct db_record *rec);

static void db_tdb2_queue_change(struct db_tdb2_ctx *db_ctx, const TDB_DATA key);
static void db_tdb2_send_notify(struct db_tdb2_ctx *db_ctx);

static struct db_context *db_open_tdb2_ex(TALLOC_CTX *mem_ctx,
                                          const char *name,
                                          int hash_size, int tdb_flags,
                                          int open_flags, mode_t mode,
                                          const struct dbwrap_tdb2_changes *chgs);

static int db_tdb2_sync_from_master(struct db_tdb2_ctx *db_ctx,
                                    const struct dbwrap_tdb2_changes *changes);

static int db_tdb2_open_master(struct db_tdb2_ctx *db_ctx, bool transaction,
                               const struct dbwrap_tdb2_changes *changes);
static int db_tdb2_commit_local(struct db_tdb2_ctx *db_ctx, uint32_t mseqnum);
static int db_tdb2_close_master(struct db_tdb2_ctx *db_ctx);
static int db_tdb2_transaction_cancel(struct db_context *db);

static void db_tdb2_receive_changes(struct messaging_context *msg,
                                    void *private_data,
                                    uint32_t msg_type,
                                    struct server_id server_id,
                                    DATA_BLOB *data);

static struct messaging_context *global_tdb2_msg_ctx;
static bool global_tdb2_msg_ctx_initialized;

void db_tdb2_setup_messaging(struct messaging_context *msg_ctx, bool server)
{
        global_tdb2_msg_ctx = msg_ctx;

        global_tdb2_msg_ctx_initialized = true;

        if (!server) {
                return;
        }

        if (!lp_parm_bool(-1, "dbwrap", "use_tdb2", false)) {
                return;
        }

        messaging_register(msg_ctx, NULL, MSG_DBWRAP_TDB2_CHANGES,
                           db_tdb2_receive_changes);
}

static struct messaging_context *db_tdb2_get_global_messaging_context(void)
{
        struct messaging_context *msg_ctx;

        if (global_tdb2_msg_ctx_initialized) {
                return global_tdb2_msg_ctx;
        }

        msg_ctx = messaging_init(NULL, procid_self(),
                                 event_context_init(NULL));

        db_tdb2_setup_messaging(msg_ctx, false);

        return global_tdb2_msg_ctx;
}

struct tdb_fetch_locked_state {
        TALLOC_CTX *mem_ctx;
        struct db_record *result;
};

static int db_tdb2_fetchlock_parse(TDB_DATA key, TDB_DATA data,
                                  void *private_data)
{
        struct tdb_fetch_locked_state *state =
                (struct tdb_fetch_locked_state *)private_data;

        state->result = (struct db_record *)talloc_size(
                state->mem_ctx,
                sizeof(struct db_record) + key.dsize + data.dsize);

        if (state->result == NULL) {
                return 0;
        }

        state->result->key.dsize = key.dsize;
        state->result->key.dptr = ((uint8 *)state->result)
                + sizeof(struct db_record);
        memcpy(state->result->key.dptr, key.dptr, key.dsize);

        state->result->value.dsize = data.dsize;

        if (data.dsize > 0) {
                state->result->value.dptr = state->result->key.dptr+key.dsize;
                memcpy(state->result->value.dptr, data.dptr, data.dsize);
        }
        else {
                state->result->value.dptr = NULL;
        }

        return 0;
}

static struct db_record *db_tdb2_fetch_locked(struct db_context *db,
                                              TALLOC_CTX *mem_ctx, TDB_DATA key)
{
        struct db_tdb2_ctx *ctx = talloc_get_type_abort(db->private_data,
                                                        struct db_tdb2_ctx);
        struct tdb_fetch_locked_state state;

        /* Do not accidently allocate/deallocate w/o need when debug level is lower than needed */
        if(DEBUGLEVEL >= 10) {
                char *keystr = hex_encode(NULL, (unsigned char*)key.dptr, key.dsize);
                DEBUG(10, (DEBUGLEVEL > 10
                           ? "Locking key %s\n" : "Locking key %.20s\n",
                           keystr));
                TALLOC_FREE(keystr);
        }

        /*
         * we only support modifications within a
         * started transaction.
         */
        if (ctx->transaction == 0) {
                DEBUG(0, ("db_tdb2_fetch_locked[%s]: no transaction started\n",
                          ctx->name));
                smb_panic("no transaction");
                return NULL;
        }

        state.mem_ctx = mem_ctx;
        state.result = NULL;

        tdb_parse_record(ctx->mtdb->tdb, key, db_tdb2_fetchlock_parse, &state);

        if (state.result == NULL) {
                db_tdb2_fetchlock_parse(key, tdb_null, &state);
        }

        if (state.result == NULL) {
                return NULL;
        }

        state.result->private_data = talloc_reference(state.result, ctx);
        state.result->store = db_tdb2_store;
        state.result->delete_rec = db_tdb2_delete;

        DEBUG(10, ("Allocated locked data 0x%p\n", state.result));

        return state.result;
}

struct tdb_fetch_state {
        TALLOC_CTX *mem_ctx;
        int result;
        TDB_DATA data;
};

static int db_tdb2_fetch_parse(TDB_DATA key, TDB_DATA data,
                               void *private_data)
{
        struct tdb_fetch_state *state =
                (struct tdb_fetch_state *)private_data;

        state->data.dptr = (uint8 *)talloc_memdup(state->mem_ctx, data.dptr,
                                                  data.dsize);
        if (state->data.dptr == NULL) {
                state->result = -1;
                return 0;
        }

        state->data.dsize = data.dsize;
        return 0;
}

static void db_tdb2_resync_before_read(struct db_tdb2_ctx *db_ctx, TDB_DATA *kbuf)
{
        if (db_ctx->mtdb) {
                return;
        }

        if (!db_ctx->out_of_sync) {
                return;
        }

        /*
         * this function operates on the local copy,
         * so hide the DB_TDB2_MASTER_SEQNUM_KEYSTR from the caller.
         */
        if (kbuf && (db_ctx->mseqkey.dsize == kbuf->dsize) &&
            (memcmp(db_ctx->mseqkey.dptr, kbuf->dptr, kbuf->dsize) == 0)) {
                return;
        }

        DEBUG(0,("resync_before_read[%s/%s]\n",
                 db_ctx->mtdb_path, db_ctx->ltdb_path));

        db_tdb2_open_master(db_ctx, false, NULL);
        db_tdb2_close_master(db_ctx);
}

static int db_tdb2_fetch(struct db_context *db, TALLOC_CTX *mem_ctx,
                         TDB_DATA key, TDB_DATA *pdata)
{
        struct db_tdb2_ctx *ctx = talloc_get_type_abort(
                db->private_data, struct db_tdb2_ctx);

        struct tdb_fetch_state state;

        db_tdb2_resync_before_read(ctx, &key);

        if (ctx->out_of_sync) {
                DEBUG(0,("out of sync[%s] failing fetch\n",
                         ctx->ltdb_path));
                errno = EIO;
                return -1;
        }

        state.mem_ctx = mem_ctx;
        state.result = 0;
        state.data = tdb_null;

        tdb_parse_record(ctx->ltdb->tdb, key, db_tdb2_fetch_parse, &state);

        if (state.result == -1) {
                return -1;
        }

        *pdata = state.data;
        return 0;
}

static NTSTATUS db_tdb2_store(struct db_record *rec, TDB_DATA data, int flag)
{
        struct db_tdb2_ctx *ctx = talloc_get_type_abort(rec->private_data,
                                                       struct db_tdb2_ctx);
        int ret;

        /*
         * This has a bug: We need to replace rec->value for correct
         * operation, but right now brlock and locking don't use the value
         * anymore after it was stored.
         */

        /* first store it to the master copy */
        ret = tdb_store(ctx->mtdb->tdb, rec->key, data, flag);
        if (ret != 0) {
                return NT_STATUS_UNSUCCESSFUL;
        }

        /* then store it to the local copy */
        ret = tdb_store(ctx->ltdb->tdb, rec->key, data, flag);
        if (ret != 0) {
                /* try to restore the old value in the master copy */
                if (rec->value.dptr) {
                        tdb_store(ctx->mtdb->tdb, rec->key,
                                  rec->value, TDB_REPLACE);
                } else {
                        tdb_delete(ctx->mtdb->tdb, rec->key);
                }
                return NT_STATUS_INTERNAL_DB_CORRUPTION;
        }

        db_tdb2_queue_change(ctx, rec->key);

        return NT_STATUS_OK;
}

static NTSTATUS db_tdb2_delete(struct db_record *rec)
{
        struct db_tdb2_ctx *ctx = talloc_get_type_abort(rec->private_data,
                                                       struct db_tdb2_ctx);
        int ret;

        ret = tdb_delete(ctx->mtdb->tdb, rec->key);
        if (ret != 0) {
                if (tdb_error(ctx->mtdb->tdb) == TDB_ERR_NOEXIST) {
                        return NT_STATUS_NOT_FOUND;
                }

                return NT_STATUS_UNSUCCESSFUL;
        }

        ret = tdb_delete(ctx->ltdb->tdb, rec->key);
        if (ret != 0) {
                /* try to restore the value in the master copy */
                tdb_store(ctx->mtdb->tdb, rec->key,
                          rec->value, TDB_REPLACE);
                return NT_STATUS_INTERNAL_DB_CORRUPTION;
        }

        db_tdb2_queue_change(ctx, rec->key);

        return NT_STATUS_OK;
}

struct db_tdb2_traverse_ctx {
        struct db_tdb2_ctx *db_ctx;
        int (*f)(struct db_record *rec, void *private_data);
        void *private_data;
};

static int db_tdb2_traverse_func(TDB_CONTEXT *tdb, TDB_DATA kbuf, TDB_DATA dbuf,
                                void *private_data)
{
        struct db_tdb2_traverse_ctx *ctx =
                (struct db_tdb2_traverse_ctx *)private_data;
        struct db_record rec;

        /* this function operates on the master copy */

        rec.key = kbuf;
        rec.value = dbuf;
        rec.store = db_tdb2_store;
        rec.delete_rec = db_tdb2_delete;
        rec.private_data = ctx->db_ctx;

        return ctx->f(&rec, ctx->private_data);
}

static int db_tdb2_traverse(struct db_context *db,
                           int (*f)(struct db_record *rec, void *private_data),
                           void *private_data)
{
        struct db_tdb2_ctx *db_ctx =
                talloc_get_type_abort(db->private_data, struct db_tdb2_ctx);
        struct db_tdb2_traverse_ctx ctx;

        /*
         * we only support modifications within a
         * started transaction.
         */
        if (db_ctx->transaction == 0) {
                DEBUG(0, ("db_tdb2_traverse[%s]: no transaction started\n",
                          db_ctx->name));
                smb_panic("no transaction");
                return -1;
        }

        /* here we traverse the master copy */
        ctx.db_ctx = db_ctx;
        ctx.f = f;
        ctx.private_data = private_data;
        return tdb_traverse(db_ctx->mtdb->tdb, db_tdb2_traverse_func, &ctx);
}

static NTSTATUS db_tdb2_store_deny(struct db_record *rec, TDB_DATA data, int flag)
{
        return NT_STATUS_MEDIA_WRITE_PROTECTED;
}

static NTSTATUS db_tdb2_delete_deny(struct db_record *rec)
{
        return NT_STATUS_MEDIA_WRITE_PROTECTED;
}

static int db_tdb2_traverse_read_func(TDB_CONTEXT *tdb, TDB_DATA kbuf, TDB_DATA dbuf,
                                void *private_data)
{
        struct db_tdb2_traverse_ctx *ctx =
                (struct db_tdb2_traverse_ctx *)private_data;
        struct db_record rec;

        /*
         * this function operates on the local copy,
         * so hide the DB_TDB2_MASTER_SEQNUM_KEYSTR from the caller.
         */
        if ((ctx->db_ctx->mseqkey.dsize == kbuf.dsize) &&
            (memcmp(ctx->db_ctx->mseqkey.dptr, kbuf.dptr, kbuf.dsize) == 0)) {
                return 0;
        }

        rec.key = kbuf;
        rec.value = dbuf;
        rec.store = db_tdb2_store_deny;
        rec.delete_rec = db_tdb2_delete_deny;
        rec.private_data = ctx->db_ctx;

        return ctx->f(&rec, ctx->private_data);
}

static int db_tdb2_traverse_read(struct db_context *db,
                           int (*f)(struct db_record *rec, void *private_data),
                           void *private_data)
{
        struct db_tdb2_ctx *db_ctx =
                talloc_get_type_abort(db->private_data, struct db_tdb2_ctx);
        struct db_tdb2_traverse_ctx ctx;
        int ret;

        db_tdb2_resync_before_read(db_ctx, NULL);

        if (db_ctx->out_of_sync) {
                DEBUG(0,("out of sync[%s] failing traverse_read\n",
                         db_ctx->ltdb_path));
                errno = EIO;
                return -1;
        }

        /* here we traverse the local copy */
        ctx.db_ctx = db_ctx;
        ctx.f = f;
        ctx.private_data = private_data;
        ret = tdb_traverse_read(db_ctx->ltdb->tdb, db_tdb2_traverse_read_func, &ctx);
        if (ret > 0) {
                /* we have filtered one entry */
                ret--;
        }

        return ret;
}

static int db_tdb2_get_seqnum(struct db_context *db)

{
        struct db_tdb2_ctx *db_ctx =
                talloc_get_type_abort(db->private_data, struct db_tdb2_ctx);
        uint32_t nlseq;
        uint32_t nmseq;
        bool ok;

        nlseq = tdb_get_seqnum(db_ctx->ltdb->tdb);

        if (nlseq == db_ctx->lseqnum) {
                return db_ctx->mseqnum;
        }

        ok = tdb_fetch_uint32_byblob(db_ctx->ltdb->tdb,
                                     db_ctx->mseqkey,
                                     &nmseq);
        if (!ok) {
                /* TODO: what should we do here? */
                return db_ctx->mseqnum;
        }

        db_ctx->lseqnum = nlseq;
        db_ctx->mseqnum = nmseq;

        return db_ctx->mseqnum;
}

static int db_tdb2_transaction_start(struct db_context *db)
{
        struct db_tdb2_ctx *db_ctx =
                talloc_get_type_abort(db->private_data, struct db_tdb2_ctx);
        int ret;

        if (db_ctx->transaction) {
                db_ctx->transaction++;
                return 0;
        }

        /* we need to open the master tdb in order to */
        ret = db_tdb2_open_master(db_ctx, true, NULL);
        if (ret != 0) {
                return ret;
        }

        ret = tdb_transaction_start(db_ctx->ltdb->tdb);
        if (ret != 0) {
                db_tdb2_close_master(db_ctx);
                return ret;
        }

        db_ctx->local_transaction = true;
        db_ctx->transaction = 1;

        return 0;
}

static void db_tdb2_queue_change(struct db_tdb2_ctx *db_ctx, const TDB_DATA key)
{
        size_t size_needed = 4 + key.dsize;
        size_t size_new = db_ctx->current_buffer_size + size_needed;
        uint32_t i;
        DATA_BLOB *keys;

        db_ctx->changes.num_changes++;

        if (db_ctx->changes.num_changes > 1 &&
            db_ctx->changes.keys == NULL) {
                /*
                 * this means we already overflowed
                 */
                return;
        }

        if (db_ctx->changes.num_changes == 1) {
                db_ctx->changes.old_seqnum = db_ctx->mseqnum;
        }

        for (i=0; i < db_ctx->changes.num_keys; i++) {
                int ret;

                if (key.dsize != db_ctx->changes.keys[i].length) {
                        continue;
                }
                ret = memcmp(key.dptr, db_ctx->changes.keys[i].data, key.dsize);
                if (ret != 0) {
                        continue;
                }

                /*
                 * the key is already in the list
                 * so we're done
                 */
                return;
        }

        if (db_ctx->max_buffer_size < size_new) {
                goto overflow;
        }

        keys = TALLOC_REALLOC_ARRAY(db_ctx, db_ctx->changes.keys,
                                    DATA_BLOB,
                                    db_ctx->changes.num_keys + 1);
        if (!keys) {
                goto overflow;
        }
        db_ctx->changes.keys = keys;

        keys[db_ctx->changes.num_keys].data = (uint8_t *)talloc_memdup(keys,
                                                                key.dptr,
                                                                key.dsize);
        if (!keys[db_ctx->changes.num_keys].data) {
                goto overflow;
        }
        keys[db_ctx->changes.num_keys].length = key.dsize;
        db_ctx->changes.num_keys++;
        db_ctx->current_buffer_size = size_new;

        return;

overflow:
        /*
         * on overflow discard the buffer and let
         * the others reload the whole tdb
         */
        db_ctx->current_buffer_size = 0;
        db_ctx->changes.num_keys = 0;
        TALLOC_FREE(db_ctx->changes.keys);
        return;
}

static void db_tdb2_send_notify(struct db_tdb2_ctx *db_ctx)
{
        enum ndr_err_code ndr_err;
        bool ok;
        DATA_BLOB blob;
        struct messaging_context *msg_ctx;
        int num_msgs = 0;
        struct server_id self = procid_self();

        msg_ctx = db_tdb2_get_global_messaging_context();

        db_ctx->changes.name = db_ctx->name;

        DEBUG(10,("%s[%s] size[%u/%u] changes[%u] keys[%u] seqnum[%u=>%u]\n",
                 __FUNCTION__,
                 db_ctx->changes.name,
                 db_ctx->current_buffer_size,
                 db_ctx->max_buffer_size,
                 db_ctx->changes.num_changes,
                 db_ctx->changes.num_keys,
                 db_ctx->changes.old_seqnum,
                 db_ctx->changes.new_seqnum));

        if (db_ctx->changes.num_changes == 0) {
                DEBUG(10,("db_tdb2_send_notify[%s]: no changes\n",
                        db_ctx->changes.name));
                goto done;
        }

        if (!msg_ctx) {
                DEBUG(1,("db_tdb2_send_notify[%s]: skipped (no msg ctx)\n",
                        db_ctx->changes.name));
                goto done;
        }

        ndr_err = ndr_push_struct_blob(
                &blob, talloc_tos(), &db_ctx->changes,
                (ndr_push_flags_fn_t)ndr_push_dbwrap_tdb2_changes);
        if (!NDR_ERR_CODE_IS_SUCCESS(ndr_err)) {
                DEBUG(0,("db_tdb2_send_notify[%s]: failed to push changes: %s\n",
                        db_ctx->changes.name,
                        nt_errstr(ndr_map_error2ntstatus(ndr_err))));
                goto done;
        }

        ok = message_send_all(msg_ctx, MSG_DBWRAP_TDB2_CHANGES,
                              blob.data, blob.length, &num_msgs);
        if (!ok) {
                DEBUG(0,("db_tdb2_send_notify[%s]: failed to send changes\n",
                        db_ctx->changes.name));
                goto done;
        }

        DEBUG(10,("db_tdb2_send_notify[%s]: pid %s send %u messages\n",
                db_ctx->name, procid_str_static(&self), num_msgs));

done:
        TALLOC_FREE(db_ctx->changes.keys);
        ZERO_STRUCT(db_ctx->changes);

        return;
}

static void db_tdb2_receive_changes(struct messaging_context *msg,
                                    void *private_data,
                                    uint32_t msg_type,
                                    struct server_id server_id,
                                    DATA_BLOB *data)
{
        enum ndr_err_code ndr_err;
        struct dbwrap_tdb2_changes changes;
        struct db_context *db;
        struct server_id self;

        if (procid_is_me(&server_id)) {
                DEBUG(0,("db_tdb2_receive_changes: ignore selfpacket\n"));
                return;
        }

        self = procid_self();

        DEBUG(10,("db_tdb2_receive_changes: from %s to %s\n",
                procid_str(debug_ctx(), &server_id),
                procid_str(debug_ctx(), &self)));

        ndr_err = ndr_pull_struct_blob_all(
                data, talloc_tos(), &changes,
                (ndr_pull_flags_fn_t)ndr_pull_dbwrap_tdb2_changes);
        if (!NDR_ERR_CODE_IS_SUCCESS(ndr_err)) {
                DEBUG(0,("db_tdb2_receive_changes: failed to pull changes: %s\n",
                        nt_errstr(ndr_map_error2ntstatus(ndr_err))));
                goto done;
        }

        if(DEBUGLEVEL >= 10) {
                NDR_PRINT_DEBUG(dbwrap_tdb2_changes, &changes);
        }

        /* open the db, this will sync it */
        db = db_open_tdb2_ex(talloc_tos(), changes.name, 0,
                             0, O_RDWR, 0600, &changes);
        TALLOC_FREE(db);
done:
        return;
}

static int db_tdb2_transaction_commit(struct db_context *db)
{
        struct db_tdb2_ctx *db_ctx =
                talloc_get_type_abort(db->private_data, struct db_tdb2_ctx);
        int ret;
        uint32_t mseqnum;

        if (db_ctx->transaction == 0) {
                return -1;
        } else if (db_ctx->transaction > 1) {
                db_ctx->transaction--;
                return 0;
        }

        mseqnum = tdb_get_seqnum(db_ctx->mtdb->tdb);
        db_ctx->changes.new_seqnum = mseqnum;

        /* first commit to the master copy */
        ret = tdb_transaction_commit(db_ctx->mtdb->tdb);
        db_ctx->master_transaction = false;
        if (ret != 0) {
                int saved_errno = errno;
                db_tdb2_transaction_cancel(db);
                errno = saved_errno;
                return ret;
        }

        /*
         * Note: as we've already commited the changes to the master copy
         *       so we ignore errors in the following functions
         */
        ret = db_tdb2_commit_local(db_ctx, mseqnum);
        if (ret == 0) {
                db_ctx->out_of_sync = false;
        } else {
                db_ctx->out_of_sync = true;
        }

        db_ctx->transaction = 0;

        db_tdb2_close_master(db_ctx);

        db_tdb2_send_notify(db_ctx);

        return 0;
}

static int db_tdb2_transaction_cancel(struct db_context *db)
{
        struct db_tdb2_ctx *db_ctx =
                talloc_get_type_abort(db->private_data, struct db_tdb2_ctx);
        int saved_errno;
        int ret;

        if (db_ctx->transaction == 0) {
                return -1;
        }
        if (db_ctx->transaction > 1) {
                db_ctx->transaction--;
                return 0;
        }

        /* cancel the transaction and close the master copy */
        ret = db_tdb2_close_master(db_ctx);
        saved_errno = errno;

        /* now cancel on the local copy and ignore any error */
        tdb_transaction_cancel(db_ctx->ltdb->tdb);
        db_ctx->local_transaction = false;

        db_ctx->transaction = 0;

        errno = saved_errno;
        return ret;
}

static int db_tdb2_open_master(struct db_tdb2_ctx *db_ctx, bool transaction,
                               const struct dbwrap_tdb2_changes *changes)
{
        int ret;

        db_ctx->mtdb = tdb_wrap_open(db_ctx,
                                     db_ctx->mtdb_path,
                                     db_ctx->open.hash_size,
                                     db_ctx->open.tdb_flags|TDB_NOMMAP|TDB_SEQNUM,
                                     db_ctx->open.open_flags,
                                     db_ctx->open.mode);
        if (db_ctx->mtdb == NULL) {
                DEBUG(0, ("Could not open master tdb[%s]: %s\n",
                          db_ctx->mtdb_path,
                          strerror(errno)));
                return -1;
        }
        DEBUG(10,("open_master[%s]\n", db_ctx->mtdb_path));

        if (!db_ctx->ltdb) {
                struct stat st;

                if (fstat(tdb_fd(db_ctx->mtdb->tdb), &st) == 0) {
                        db_ctx->open.mode = st.st_mode;
                }

                /* make sure the local one uses the same hash size as the master one */
                db_ctx->open.hash_size = tdb_hash_size(db_ctx->mtdb->tdb);

                db_ctx->ltdb = tdb_wrap_open(db_ctx,
                                             db_ctx->ltdb_path,
                                             db_ctx->open.hash_size,
                                             db_ctx->open.tdb_flags|TDB_SEQNUM,
                                             db_ctx->open.open_flags|O_CREAT,
                                             db_ctx->open.mode);
                if (db_ctx->ltdb == NULL) {
                        DEBUG(0, ("Could not open local tdb[%s]: %s\n",
                                  db_ctx->ltdb_path,
                                  strerror(errno)));
                        TALLOC_FREE(db_ctx->mtdb);
                        return -1;
                }
                DEBUG(10,("open_local[%s]\n", db_ctx->ltdb_path));
        }

        if (transaction) {
                ret = tdb_transaction_start(db_ctx->mtdb->tdb);
                if (ret != 0) {
                        DEBUG(0,("open failed to start transaction[%s]\n",
                                 db_ctx->mtdb_path));
                        db_tdb2_close_master(db_ctx);
                        return ret;
                }
                db_ctx->master_transaction = true;
        }

        ret = db_tdb2_sync_from_master(db_ctx, changes);
        if (ret != 0) {
                DEBUG(0,("open failed to sync from master[%s]\n",
                         db_ctx->ltdb_path));
                db_tdb2_close_master(db_ctx);
                return ret;
        }

        return 0;
}

static int db_tdb2_commit_local(struct db_tdb2_ctx *db_ctx, uint32_t mseqnum)
{
        bool ok;
        int ret;

        /* first fetch the master seqnum */
        db_ctx->mseqnum = mseqnum;

        /* now we try to store the master seqnum in the local tdb */
        ok = tdb_store_uint32_byblob(db_ctx->ltdb->tdb,
                                     db_ctx->mseqkey,
                                     db_ctx->mseqnum);
        if (!ok) {
                tdb_transaction_cancel(db_ctx->ltdb->tdb);
                db_ctx->local_transaction = false;
                DEBUG(0,("local failed[%s] store mseq[%u]\n",
                         db_ctx->ltdb_path, db_ctx->mseqnum));
                return -1;
        }

        /* now commit all changes to the local tdb */
        ret = tdb_transaction_commit(db_ctx->ltdb->tdb);
        db_ctx->local_transaction = false;
        if (ret != 0) {
                DEBUG(0,("local failed[%s] commit mseq[%u]\n",
                         db_ctx->ltdb_path, db_ctx->mseqnum));
                return ret;
        }

        /*
         * and update the cached local seqnum this is needed to
         * let us cache the master seqnum.
         */
        db_ctx->lseqnum = tdb_get_seqnum(db_ctx->ltdb->tdb);
        DEBUG(10,("local updated[%s] mseq[%u]\n",
                  db_ctx->ltdb_path, db_ctx->mseqnum));

        return 0;
}

static int db_tdb2_close_master(struct db_tdb2_ctx *db_ctx)
{
        if (db_ctx->master_transaction) {
                tdb_transaction_cancel(db_ctx->mtdb->tdb);
        }
        db_ctx->master_transaction = false;
        /* now we can close the master handle */
        TALLOC_FREE(db_ctx->mtdb);

        DEBUG(10,("close_master[%s] ok\n", db_ctx->mtdb_path));
        return 0;
}

static int db_tdb2_traverse_sync_all_func(TDB_CONTEXT *tdb,
                                          TDB_DATA kbuf, TDB_DATA dbuf,
                                          void *private_data)
{
        struct db_tdb2_traverse_ctx *ctx =
                (struct db_tdb2_traverse_ctx *)private_data;
        uint32_t *seqnum = (uint32_t *)ctx->private_data;
        int ret;

        DEBUG(10,("sync_entry[%s]\n", ctx->db_ctx->mtdb_path));

        /* Do not accidently allocate/deallocate w/o need when debug level is lower than needed */
        if(DEBUGLEVEL >= 10) {
                char *keystr = hex_encode(NULL, (unsigned char*)kbuf.dptr, kbuf.dsize);
                DEBUG(10, (DEBUGLEVEL > 10
                           ? "Locking key %s\n" : "Locking key %.20s\n",
                           keystr));
                TALLOC_FREE(keystr);
        }

        ret = tdb_store(ctx->db_ctx->ltdb->tdb, kbuf, dbuf, TDB_INSERT);
        if (ret != 0) {
                DEBUG(0,("sync_entry[%s] %d: %s\n",
                        ctx->db_ctx->ltdb_path, ret,
                        tdb_errorstr(ctx->db_ctx->ltdb->tdb)));
                return ret;
        }

        *seqnum = tdb_get_seqnum(ctx->db_ctx->mtdb->tdb);

        return 0;
}

static int db_tdb2_sync_all(struct db_tdb2_ctx *db_ctx, uint32_t *seqnum)
{
        struct db_tdb2_traverse_ctx ctx;
        int ret;

        ret = tdb_wipe_all(db_ctx->ltdb->tdb);
        if (ret != 0) {
                DEBUG(0,("tdb_wipe_all[%s] failed %d: %s\n",
                         db_ctx->ltdb_path, ret,
                         tdb_errorstr(db_ctx->ltdb->tdb)));
                return ret;
        }

        ctx.db_ctx = db_ctx;
        ctx.f = NULL;
        ctx.private_data = seqnum;
        ret = tdb_traverse_read(db_ctx->mtdb->tdb,
                                db_tdb2_traverse_sync_all_func,
                                &ctx);
        DEBUG(10,("db_tdb2_sync_all[%s] count[%d]\n",
                  db_ctx->mtdb_path, ret));
        if (ret < 0) {
                return ret;
        }

        return 0;
}

static int db_tdb2_sync_changes(struct db_tdb2_ctx *db_ctx,
                                const struct dbwrap_tdb2_changes *changes,
                                uint32_t *seqnum)
{
        uint32_t cseqnum;
        uint32_t mseqnum;
        uint32_t i;
        int ret;
        bool need_full_sync = false;

        DEBUG(10,("db_tdb2_sync_changes[%s] changes[%u]\n",
                  changes->name, changes->num_changes));
        if(DEBUGLEVEL >= 10) {
                NDR_PRINT_DEBUG(dbwrap_tdb2_changes, discard_const(changes));
        }

        /* for the master tdb for reading */
        ret = tdb_lockall_read(db_ctx->mtdb->tdb);
        if (ret != 0) {
                DEBUG(0,("tdb_lockall_read[%s] %d\n", db_ctx->mtdb_path, ret));
                return ret;
        }

        /* first fetch seqnum we know about */
        cseqnum = db_tdb2_get_seqnum(db_ctx->db);

        /* then fetch the master seqnum */
        mseqnum = tdb_get_seqnum(db_ctx->mtdb->tdb);

        if (cseqnum == mseqnum) {
                DEBUG(10,("db_tdb2_sync_changes[%s] uptodate[%u]\n",
                          db_ctx->mtdb_path, mseqnum));
                /* we hit a race before and now noticed we're uptodate */
                goto done;
        }

        /* now see if the changes describe what we need */
        if (changes->old_seqnum != cseqnum) {
                need_full_sync = true;
        }

        if (changes->new_seqnum != mseqnum) {
                need_full_sync = true;
        }

        /* this was the overflow case */
        if (changes->num_keys == 0) {
                need_full_sync = true;
        }

        if (need_full_sync) {
                tdb_unlockall_read(db_ctx->mtdb->tdb);
                DEBUG(0,("fallback to full sync[%s] seq[%u=>%u] keys[%u]\n",
                        db_ctx->ltdb_path, cseqnum, mseqnum,
                        changes->num_keys));
                return db_tdb2_sync_all(db_ctx, &mseqnum);
        }

        for (i=0; i < changes->num_keys; i++) {
                const char *op = NULL;
                bool del = false;
                TDB_DATA key;
                TDB_DATA val;

                key.dsize = changes->keys[i].length;
                key.dptr = changes->keys[i].data;

                val = tdb_fetch(db_ctx->mtdb->tdb, key);
                ret = tdb_error(db_ctx->mtdb->tdb);
                if (ret == TDB_ERR_NOEXIST) {
                        del = true;
                } else if (ret != 0) {
                        DEBUG(0,("sync_changes[%s] failure %d\n",
                                 db_ctx->mtdb_path, ret));
                        goto failed;
                }

                if (del) {
                        op = "delete";
                        ret = tdb_delete(db_ctx->ltdb->tdb, key);
                        DEBUG(10,("sync_changes[%s] delete key[%u] %d\n",
                                  db_ctx->mtdb_path, i, ret));
                } else {
                        op = "store";
                        ret = tdb_store(db_ctx->ltdb->tdb, key,
                                        val, TDB_REPLACE);
                        DEBUG(10,("sync_changes[%s] store key[%u] %d\n",
                                  db_ctx->mtdb_path, i, ret));
                }
                SAFE_FREE(val.dptr);
                if (ret != 0) {
                        DEBUG(0,("sync_changes[%s] %s key[%u] failed %d\n",
                                 db_ctx->mtdb_path, op, i, ret));
                        goto failed;
                }
        }

done:
        tdb_unlockall_read(db_ctx->mtdb->tdb);

        *seqnum = mseqnum;
        return 0;
failed:
        tdb_unlockall_read(db_ctx->mtdb->tdb);
        return ret;
}

static int db_tdb2_sync_from_master(struct db_tdb2_ctx *db_ctx,
                                    const struct dbwrap_tdb2_changes *changes)
{
        int ret;
        uint32_t cseqnum;
        uint32_t mseqnum;
        bool force = false;

        /* first fetch seqnum we know about */
        cseqnum = db_tdb2_get_seqnum(db_ctx->db);

        /* then fetch the master seqnum */
        mseqnum = tdb_get_seqnum(db_ctx->mtdb->tdb);

        if (db_ctx->lseqnum == 0) {
                force = true;
        }

        if (!force && cseqnum == mseqnum) {
                DEBUG(10,("uptodate[%s] mseq[%u]\n",
                          db_ctx->ltdb_path, mseqnum));
                /* the local copy is uptodate, close the master db */
                return 0;
        }
        DEBUG(10,("not uptodate[%s] seq[%u=>%u]\n",
                  db_ctx->ltdb_path, cseqnum, mseqnum));

        ret = tdb_transaction_start(db_ctx->ltdb->tdb);
        if (ret != 0) {
                DEBUG(0,("failed to start transaction[%s] %d: %s\n",
                         db_ctx->ltdb_path, ret,
                         tdb_errorstr(db_ctx->ltdb->tdb)));
                db_ctx->out_of_sync = true;
                return ret;
        }
        db_ctx->local_transaction = true;

        if (changes && !force) {
                ret = db_tdb2_sync_changes(db_ctx, changes, &mseqnum);
                if (ret != 0) {
                        db_ctx->out_of_sync = true;
                        tdb_transaction_cancel(db_ctx->ltdb->tdb);
                        db_ctx->local_transaction = false;
                        return ret;
                }
        } else {
                ret = db_tdb2_sync_all(db_ctx, &mseqnum);
                if (ret != 0) {
                        db_ctx->out_of_sync = true;
                        tdb_transaction_cancel(db_ctx->ltdb->tdb);
                        db_ctx->local_transaction = false;
                        return ret;
                }
        }

        ret = db_tdb2_commit_local(db_ctx, mseqnum);
        if (ret != 0) {
                db_ctx->out_of_sync = true;
                return ret;
        }

        db_ctx->out_of_sync = false;

        return 0;
}

static int db_tdb2_ctx_destructor(struct db_tdb2_ctx *db_tdb2)
{
        db_tdb2_close_master(db_tdb2);
        if (db_tdb2->local_transaction) {
                tdb_transaction_cancel(db_tdb2->ltdb->tdb);
        }
        db_tdb2->local_transaction = false;
        TALLOC_FREE(db_tdb2->ltdb);
        return 0;
}

static struct db_context *db_open_tdb2_ex(TALLOC_CTX *mem_ctx,
                                          const char *name,
                                          int hash_size, int tdb_flags,
                                          int open_flags, mode_t mode,
                                          const struct dbwrap_tdb2_changes *chgs)
{
        struct db_context *result = NULL;
        struct db_tdb2_ctx *db_tdb2;
        int ret;
        const char *md;
        const char *ld;
        const char *bn;

        bn = strrchr_m(name, '/');
        if (bn) {
                bn++;
                DEBUG(3,("db_open_tdb2: use basename[%s] of abspath[%s]:\n",
                        bn, name));
        } else {
                bn = name;
        }

        md = lp_parm_const_string(-1, "dbwrap_tdb2", "master directory", NULL);
        if (!md) {
                DEBUG(0,("'dbwrap_tdb2:master directory' empty\n"));
                goto fail;
        }

        ld = lp_parm_const_string(-1, "dbwrap_tdb2", "local directory", NULL);
        if (!ld) {
                DEBUG(0,("'dbwrap_tdb2:local directory' empty\n"));
                goto fail;
        }

        result = TALLOC_ZERO_P(mem_ctx, struct db_context);
        if (result == NULL) {
                DEBUG(0, ("talloc failed\n"));
                goto fail;
        }

        result->private_data = db_tdb2 = TALLOC_ZERO_P(result, struct db_tdb2_ctx);
        if (db_tdb2 == NULL) {
                DEBUG(0, ("talloc failed\n"));
                goto fail;
        }

        db_tdb2->db = result;

        db_tdb2->open.hash_size = hash_size;
        db_tdb2->open.tdb_flags = tdb_flags;
        db_tdb2->open.open_flags= open_flags;
        db_tdb2->open.mode      = mode;

        db_tdb2->max_buffer_size = lp_parm_ulong(-1, "dbwrap_tdb2",
                                                 "notify buffer size", 512);

        db_tdb2->name = talloc_strdup(db_tdb2, bn);
        if (db_tdb2->name == NULL) {
                DEBUG(0, ("talloc_strdup failed\n"));
                goto fail;
        }

        db_tdb2->mtdb_path = talloc_asprintf(db_tdb2, "%s/%s",
                                             md, bn);
        if (db_tdb2->mtdb_path == NULL) {
                DEBUG(0, ("talloc_asprintf failed\n"));
                goto fail;
        }

        db_tdb2->ltdb_path = talloc_asprintf(db_tdb2, "%s/%s.tdb2",
                                             ld, bn);
        if (db_tdb2->ltdb_path == NULL) {
                DEBUG(0, ("talloc_asprintf failed\n"));
                goto fail;
        }

        db_tdb2->mseqkey = string_term_tdb_data(DB_TDB2_MASTER_SEQNUM_KEYSTR);

        /*
         * this implicit opens the local one if as it's not yet open
         * it syncs the local copy.
         */
        ret = db_tdb2_open_master(db_tdb2, false, chgs);
        if (ret != 0) {
                goto fail;
        }

        ret = db_tdb2_close_master(db_tdb2);
        if (ret != 0) {
                goto fail;
        }

        DEBUG(10,("db_open_tdb2[%s] opened with mseq[%u]\n",
                  db_tdb2->name, db_tdb2->mseqnum));

        result->fetch_locked = db_tdb2_fetch_locked;
        result->fetch = db_tdb2_fetch;
        result->traverse = db_tdb2_traverse;
        result->traverse_read = db_tdb2_traverse_read;
        result->get_seqnum = db_tdb2_get_seqnum;
        result->persistent = ((tdb_flags & TDB_CLEAR_IF_FIRST) == 0);
        result->transaction_start = db_tdb2_transaction_start;
        result->transaction_commit = db_tdb2_transaction_commit;
        result->transaction_cancel = db_tdb2_transaction_cancel;

        talloc_set_destructor(db_tdb2, db_tdb2_ctx_destructor);

        return result;

 fail:
        if (result != NULL) {
                TALLOC_FREE(result);
        }
        return NULL;
}

struct db_context *db_open_tdb2(TALLOC_CTX *mem_ctx,
                                const char *name,
                                int hash_size, int tdb_flags,
                                int open_flags, mode_t mode)
{
        return db_open_tdb2_ex(mem_ctx, name, hash_size,
                               tdb_flags, open_flags, mode, NULL);
}