dbwrap_ctdb: avoid smbd/ctdb deadlocks: check whether we can work locally in db_ctdb_...

[Samba.git] / source3 / lib / dbwrap / dbwrap_ctdb.c

/*
   Unix SMB/CIFS implementation.
   Database interface wrapper around ctdbd
   Copyright (C) Volker Lendecke 2007-2009
   Copyright (C) Michael Adam 2009

   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 "system/filesys.h"
#include "lib/tdb_wrap/tdb_wrap.h"
#include "util_tdb.h"
#include "dbwrap/dbwrap.h"
#include "dbwrap/dbwrap_ctdb.h"
#include "dbwrap/dbwrap_rbt.h"
#include "lib/param/param.h"

#ifdef CLUSTER_SUPPORT

/*
 * It is not possible to include ctdb.h and tdb_compat.h (included via
 * some other include above) without warnings. This fixes those
 * warnings.
 */

#ifdef typesafe_cb
#undef typesafe_cb
#endif

#ifdef typesafe_cb_preargs
#undef typesafe_cb_preargs
#endif

#ifdef typesafe_cb_postargs
#undef typesafe_cb_postargs
#endif

#include "ctdb.h"
#include "ctdb_private.h"
#include "ctdbd_conn.h"
#include "dbwrap/dbwrap.h"
#include "dbwrap/dbwrap_private.h"
#include "dbwrap/dbwrap_ctdb.h"
#include "g_lock.h"
#include "messages.h"

struct db_ctdb_transaction_handle {
        struct db_ctdb_ctx *ctx;
        /*
         * we store the writes done under a transaction:
         */
        struct ctdb_marshall_buffer *m_write;
        uint32_t nesting;
        bool nested_cancel;
        char *lock_name;
};

struct db_ctdb_ctx {
        struct db_context *db;
        struct tdb_wrap *wtdb;
        uint32_t db_id;
        struct db_ctdb_transaction_handle *transaction;
        struct g_lock_ctx *lock_ctx;

        /* thresholds for warning messages */
        int warn_unlock_msecs;
        int warn_migrate_msecs;
        int warn_migrate_attempts;
        int warn_locktime_msecs;
};

struct db_ctdb_rec {
        struct db_ctdb_ctx *ctdb_ctx;
        struct ctdb_ltdb_header header;
        struct timeval lock_time;
};

static NTSTATUS tdb_error_to_ntstatus(struct tdb_context *tdb)
{
        enum TDB_ERROR tret = tdb_error(tdb);

        return map_nt_error_from_tdb(tret);
}

struct db_ctdb_ltdb_parse_state {
        void (*parser)(TDB_DATA key, struct ctdb_ltdb_header *header,
                       TDB_DATA data, void *private_data);
        void *private_data;
};

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

        if (data.dsize < sizeof(struct ctdb_ltdb_header)) {
                return -1;
        }

        state->parser(
                key, (struct ctdb_ltdb_header *)data.dptr,
                make_tdb_data(data.dptr + sizeof(struct ctdb_ltdb_header),
                              data.dsize - sizeof(struct ctdb_ltdb_header)),
                state->private_data);
        return 0;
}

static NTSTATUS db_ctdb_ltdb_parse(
        struct db_ctdb_ctx *db, TDB_DATA key,
        void (*parser)(TDB_DATA key, struct ctdb_ltdb_header *header,
                       TDB_DATA data, void *private_data),
        void *private_data)
{
        struct db_ctdb_ltdb_parse_state state;
        int ret;

        state.parser = parser;
        state.private_data = private_data;

        ret = tdb_parse_record(db->wtdb->tdb, key, db_ctdb_ltdb_parser,
                               &state);
        if (ret == -1) {
                return NT_STATUS_NOT_FOUND;
        }
        return NT_STATUS_OK;
}

/*
 * Store a record together with the ctdb record header
 * in the local copy of the database.
 */
static NTSTATUS db_ctdb_ltdb_store(struct db_ctdb_ctx *db,
                                   TDB_DATA key,
                                   struct ctdb_ltdb_header *header,
                                   TDB_DATA data)
{
        TDB_DATA rec;
        int ret;

        rec.dsize = data.dsize + sizeof(struct ctdb_ltdb_header);
        rec.dptr = (uint8_t *)talloc_size(talloc_tos(), rec.dsize);

        if (rec.dptr == NULL) {
                return NT_STATUS_NO_MEMORY;
        }

        memcpy(rec.dptr, header, sizeof(struct ctdb_ltdb_header));
        memcpy(sizeof(struct ctdb_ltdb_header) + (uint8_t *)rec.dptr, data.dptr, data.dsize);

        ret = tdb_store(db->wtdb->tdb, key, rec, TDB_REPLACE);

        talloc_free(rec.dptr);

        return (ret == 0) ? NT_STATUS_OK
                          : tdb_error_to_ntstatus(db->wtdb->tdb);

}

/*
  form a ctdb_rec_data record from a key/data pair
 */
static struct ctdb_rec_data *db_ctdb_marshall_record(TALLOC_CTX *mem_ctx, uint32_t reqid,
                                                  TDB_DATA key,
                                                  struct ctdb_ltdb_header *header,
                                                  TDB_DATA data)
{
        size_t length;
        struct ctdb_rec_data *d;

        length = offsetof(struct ctdb_rec_data, data) + key.dsize +
                data.dsize + sizeof(*header);
        d = (struct ctdb_rec_data *)talloc_size(mem_ctx, length);
        if (d == NULL) {
                return NULL;
        }
        d->length = length;
        d->reqid = reqid;
        d->keylen = key.dsize;
        memcpy(&d->data[0], key.dptr, key.dsize);

        d->datalen = data.dsize + sizeof(*header);
        memcpy(&d->data[key.dsize], header, sizeof(*header));
        memcpy(&d->data[key.dsize+sizeof(*header)], data.dptr, data.dsize);
        return d;
}


/* helper function for marshalling multiple records */
static struct ctdb_marshall_buffer *db_ctdb_marshall_add(TALLOC_CTX *mem_ctx,
                                               struct ctdb_marshall_buffer *m,
                                               uint64_t db_id,
                                               uint32_t reqid,
                                               TDB_DATA key,
                                               struct ctdb_ltdb_header *header,
                                               TDB_DATA data)
{
        struct ctdb_rec_data *r;
        size_t m_size, r_size;
        struct ctdb_marshall_buffer *m2 = NULL;

        r = db_ctdb_marshall_record(talloc_tos(), reqid, key, header, data);
        if (r == NULL) {
                talloc_free(m);
                return NULL;
        }

        if (m == NULL) {
                m = (struct ctdb_marshall_buffer *)talloc_zero_size(
                        mem_ctx, offsetof(struct ctdb_marshall_buffer, data));
                if (m == NULL) {
                        goto done;
                }
                m->db_id = db_id;
        }

        m_size = talloc_get_size(m);
        r_size = talloc_get_size(r);

        m2 = (struct ctdb_marshall_buffer *)talloc_realloc_size(
                mem_ctx, m,  m_size + r_size);
        if (m2 == NULL) {
                talloc_free(m);
                goto done;
        }

        memcpy(m_size + (uint8_t *)m2, r, r_size);

        m2->count++;

done:
        talloc_free(r);
        return m2;
}

/* we've finished marshalling, return a data blob with the marshalled records */
static TDB_DATA db_ctdb_marshall_finish(struct ctdb_marshall_buffer *m)
{
        TDB_DATA data;
        data.dptr = (uint8_t *)m;
        data.dsize = talloc_get_size(m);
        return data;
}

/*
   loop over a marshalling buffer

     - pass r==NULL to start
     - loop the number of times indicated by m->count
*/
static struct ctdb_rec_data *db_ctdb_marshall_loop_next_key(
        struct ctdb_marshall_buffer *m, struct ctdb_rec_data *r, TDB_DATA *key)
{
        if (r == NULL) {
                r = (struct ctdb_rec_data *)&m->data[0];
        } else {
                r = (struct ctdb_rec_data *)(r->length + (uint8_t *)r);
        }

        key->dptr   = &r->data[0];
        key->dsize  = r->keylen;
        return r;
}

static bool db_ctdb_marshall_buf_parse(
        struct ctdb_rec_data *r, uint32_t *reqid,
        struct ctdb_ltdb_header **header, TDB_DATA *data)
{
        if (r->datalen < sizeof(struct ctdb_ltdb_header)) {
                return false;
        }

        *reqid = r->reqid;

        data->dptr  = &r->data[r->keylen] + sizeof(struct ctdb_ltdb_header);
        data->dsize = r->datalen - sizeof(struct ctdb_ltdb_header);

        *header = (struct ctdb_ltdb_header *)&r->data[r->keylen];

        return true;
}

/**
 * CTDB transaction destructor
 */
static int db_ctdb_transaction_destructor(struct db_ctdb_transaction_handle *h)
{
        NTSTATUS status;

        status = g_lock_unlock(h->ctx->lock_ctx, h->lock_name);
        if (!NT_STATUS_IS_OK(status)) {
                DEBUG(0, ("g_lock_unlock failed for %s: %s\n", h->lock_name,
                          nt_errstr(status)));
                return -1;
        }
        return 0;
}

/**
 * CTDB dbwrap API: transaction_start function
 * starts a transaction on a persistent database
 */
static int db_ctdb_transaction_start(struct db_context *db)
{
        struct db_ctdb_transaction_handle *h;
        NTSTATUS status;
        struct db_ctdb_ctx *ctx = talloc_get_type_abort(db->private_data,
                                                        struct db_ctdb_ctx);

        if (!db->persistent) {
                DEBUG(0,("transactions not supported on non-persistent database 0x%08x\n", 
                         ctx->db_id));
                return -1;
        }

        if (ctx->transaction) {
                ctx->transaction->nesting++;
                DEBUG(5, (__location__ " transaction start on db 0x%08x: nesting %d -> %d\n",
                          ctx->db_id, ctx->transaction->nesting - 1, ctx->transaction->nesting));
                return 0;
        }

        h = talloc_zero(db, struct db_ctdb_transaction_handle);
        if (h == NULL) {
                DEBUG(0,(__location__ " oom for transaction handle\n"));
                return -1;
        }

        h->ctx = ctx;

        h->lock_name = talloc_asprintf(h, "transaction_db_0x%08x",
                                       (unsigned int)ctx->db_id);
        if (h->lock_name == NULL) {
                DEBUG(0, ("talloc_asprintf failed\n"));
                TALLOC_FREE(h);
                return -1;
        }

        /*
         * Wait a day, i.e. forever...
         */
        status = g_lock_lock(ctx->lock_ctx, h->lock_name, G_LOCK_WRITE,
                             timeval_set(86400, 0));
        if (!NT_STATUS_IS_OK(status)) {
                DEBUG(0, ("g_lock_lock failed: %s\n", nt_errstr(status)));
                TALLOC_FREE(h);
                return -1;
        }

        talloc_set_destructor(h, db_ctdb_transaction_destructor);

        ctx->transaction = h;

        DEBUG(5,(__location__ " transaction started on db 0x%08x\n", ctx->db_id));

        return 0;
}

static bool parse_newest_in_marshall_buffer(
        struct ctdb_marshall_buffer *buf, TDB_DATA key,
        void (*parser)(TDB_DATA key, struct ctdb_ltdb_header *header,
                       TDB_DATA data, void *private_data),
        void *private_data)
{
        struct ctdb_rec_data *rec = NULL;
        struct ctdb_ltdb_header *h = NULL;
        TDB_DATA data;
        int i;

        if (buf == NULL) {
                return false;
        }

        /*
         * Walk the list of records written during this
         * transaction. If we want to read one we have already
         * written, return the last written sample. Thus we do not do
         * a "break;" for the first hit, this record might have been
         * overwritten later.
         */

        for (i=0; i<buf->count; i++) {
                TDB_DATA tkey;
                uint32_t reqid;

                rec = db_ctdb_marshall_loop_next_key(buf, rec, &tkey);
                if (rec == NULL) {
                        return false;
                }

                if (!tdb_data_equal(key, tkey)) {
                        continue;
                }

                if (!db_ctdb_marshall_buf_parse(rec, &reqid, &h, &data)) {
                        return false;
                }
        }

        if (h == NULL) {
                return false;
        }

        parser(key, h, data, private_data);

        return true;
}

struct pull_newest_from_marshall_buffer_state {
        struct ctdb_ltdb_header *pheader;
        TALLOC_CTX *mem_ctx;
        TDB_DATA *pdata;
};

static void pull_newest_from_marshall_buffer_parser(
        TDB_DATA key, struct ctdb_ltdb_header *header,
        TDB_DATA data, void *private_data)
{
        struct pull_newest_from_marshall_buffer_state *state =
                (struct pull_newest_from_marshall_buffer_state *)private_data;

        if (state->pheader != NULL) {
                memcpy(state->pheader, header, sizeof(*state->pheader));
        }
        if (state->pdata != NULL) {
                state->pdata->dsize = data.dsize;
                state->pdata->dptr = (uint8_t *)talloc_memdup(
                        state->mem_ctx, data.dptr, data.dsize);
        }
}

static bool pull_newest_from_marshall_buffer(struct ctdb_marshall_buffer *buf,
                                             TDB_DATA key,
                                             struct ctdb_ltdb_header *pheader,
                                             TALLOC_CTX *mem_ctx,
                                             TDB_DATA *pdata)
{
        struct pull_newest_from_marshall_buffer_state state;

        state.pheader = pheader;
        state.mem_ctx = mem_ctx;
        state.pdata = pdata;

        if (!parse_newest_in_marshall_buffer(
                    buf, key, pull_newest_from_marshall_buffer_parser,
                    &state)) {
                return false;
        }
        if ((pdata != NULL) && (pdata->dsize != 0) && (pdata->dptr == NULL)) {
                /* ENOMEM */
                return false;
        }
        return true;
}

static NTSTATUS db_ctdb_store_transaction(struct db_record *rec, TDB_DATA data, int flag);
static NTSTATUS db_ctdb_delete_transaction(struct db_record *rec);

static struct db_record *db_ctdb_fetch_locked_transaction(struct db_ctdb_ctx *ctx,
                                                          TALLOC_CTX *mem_ctx,
                                                          TDB_DATA key)
{
        struct db_record *result;
        TDB_DATA ctdb_data;

        if (!(result = talloc(mem_ctx, struct db_record))) {
                DEBUG(0, ("talloc failed\n"));
                return NULL;
        }

        result->db = ctx->db;
        result->private_data = ctx->transaction;

        result->key.dsize = key.dsize;
        result->key.dptr = (uint8_t *)talloc_memdup(result, key.dptr,
                                                    key.dsize);
        if (result->key.dptr == NULL) {
                DEBUG(0, ("talloc failed\n"));
                TALLOC_FREE(result);
                return NULL;
        }

        result->store = db_ctdb_store_transaction;
        result->delete_rec = db_ctdb_delete_transaction;

        if (pull_newest_from_marshall_buffer(ctx->transaction->m_write, key,
                                             NULL, result, &result->value)) {
                return result;
        }

        ctdb_data = tdb_fetch_compat(ctx->wtdb->tdb, key);
        if (ctdb_data.dptr == NULL) {
                /* create the record */
                result->value = tdb_null;
                return result;
        }

        result->value.dsize = ctdb_data.dsize - sizeof(struct ctdb_ltdb_header);
        result->value.dptr = NULL;

        if ((result->value.dsize != 0)
            && !(result->value.dptr = (uint8_t *)talloc_memdup(
                         result, ctdb_data.dptr + sizeof(struct ctdb_ltdb_header),
                         result->value.dsize))) {
                DEBUG(0, ("talloc failed\n"));
                TALLOC_FREE(result);
        }

        SAFE_FREE(ctdb_data.dptr);

        return result;
}

static int db_ctdb_record_destructor(struct db_record **recp)
{
        struct db_record *rec = talloc_get_type_abort(*recp, struct db_record);
        struct db_ctdb_transaction_handle *h = talloc_get_type_abort(
                rec->private_data, struct db_ctdb_transaction_handle);
        int ret = h->ctx->db->transaction_commit(h->ctx->db);
        if (ret != 0) {
                DEBUG(0,(__location__ " transaction_commit failed\n"));
        }
        return 0;
}

/*
  auto-create a transaction for persistent databases
 */
static struct db_record *db_ctdb_fetch_locked_persistent(struct db_ctdb_ctx *ctx,
                                                         TALLOC_CTX *mem_ctx,
                                                         TDB_DATA key)
{
        int res;
        struct db_record *rec, **recp;

        res = db_ctdb_transaction_start(ctx->db);
        if (res == -1) {
                return NULL;
        }

        rec = db_ctdb_fetch_locked_transaction(ctx, mem_ctx, key);
        if (rec == NULL) {
                ctx->db->transaction_cancel(ctx->db);
                return NULL;
        }

        /* destroy this transaction when we release the lock */
        recp = talloc(rec, struct db_record *);
        if (recp == NULL) {
                ctx->db->transaction_cancel(ctx->db);
                talloc_free(rec);
                return NULL;
        }
        *recp = rec;
        talloc_set_destructor(recp, db_ctdb_record_destructor);
        return rec;
}


/*
  stores a record inside a transaction
 */
static NTSTATUS db_ctdb_transaction_store(struct db_ctdb_transaction_handle *h,
                                          TDB_DATA key, TDB_DATA data)
{
        TALLOC_CTX *tmp_ctx = talloc_new(h);
        TDB_DATA rec;
        struct ctdb_ltdb_header header;

        ZERO_STRUCT(header);

        /* we need the header so we can update the RSN */

        if (!pull_newest_from_marshall_buffer(h->m_write, key, &header,
                                              NULL, NULL)) {

                rec = tdb_fetch_compat(h->ctx->wtdb->tdb, key);

                if (rec.dptr != NULL) {
                        memcpy(&header, rec.dptr,
                               sizeof(struct ctdb_ltdb_header));
                        rec.dsize -= sizeof(struct ctdb_ltdb_header);

                        /*
                         * a special case, we are writing the same
                         * data that is there now
                         */
                        if (data.dsize == rec.dsize &&
                            memcmp(data.dptr,
                                   rec.dptr + sizeof(struct ctdb_ltdb_header),
                                   data.dsize) == 0) {
                                SAFE_FREE(rec.dptr);
                                talloc_free(tmp_ctx);
                                return NT_STATUS_OK;
                        }
                }
                SAFE_FREE(rec.dptr);
        }

        header.dmaster = get_my_vnn();
        header.rsn++;

        h->m_write = db_ctdb_marshall_add(h, h->m_write, h->ctx->db_id, 0, key, &header, data);
        if (h->m_write == NULL) {
                DEBUG(0,(__location__ " Failed to add to marshalling record\n"));
                talloc_free(tmp_ctx);
                return NT_STATUS_NO_MEMORY;
        }

        talloc_free(tmp_ctx);
        return NT_STATUS_OK;
}


/* 
   a record store inside a transaction
 */
static NTSTATUS db_ctdb_store_transaction(struct db_record *rec, TDB_DATA data, int flag)
{
        struct db_ctdb_transaction_handle *h = talloc_get_type_abort(
                rec->private_data, struct db_ctdb_transaction_handle);
        NTSTATUS status;

        status = db_ctdb_transaction_store(h, rec->key, data);
        return status;
}

/*
   a record delete inside a transaction
 */
static NTSTATUS db_ctdb_delete_transaction(struct db_record *rec)
{
        struct db_ctdb_transaction_handle *h = talloc_get_type_abort(
                rec->private_data, struct db_ctdb_transaction_handle);
        NTSTATUS status;

        status =  db_ctdb_transaction_store(h, rec->key, tdb_null);
        return status;
}

static void db_ctdb_fetch_db_seqnum_parser(
        TDB_DATA key, struct ctdb_ltdb_header *header,
        TDB_DATA data, void *private_data)
{
        uint64_t *seqnum = (uint64_t *)private_data;

        if (data.dsize != sizeof(uint64_t)) {
                *seqnum = 0;
                return;
        }
        memcpy(seqnum, data.dptr, sizeof(*seqnum));
}

/**
 * Fetch the db sequence number of a persistent db directly from the db.
 */
static NTSTATUS db_ctdb_fetch_db_seqnum_from_db(struct db_ctdb_ctx *db,
                                                uint64_t *seqnum)
{
        NTSTATUS status;
        TDB_DATA key;

        if (seqnum == NULL) {
                return NT_STATUS_INVALID_PARAMETER;
        }

        key = string_term_tdb_data(CTDB_DB_SEQNUM_KEY);

        status = db_ctdb_ltdb_parse(
                db, key, db_ctdb_fetch_db_seqnum_parser, seqnum);

        if (NT_STATUS_IS_OK(status)) {
                return NT_STATUS_OK;
        }
        if (NT_STATUS_EQUAL(status, NT_STATUS_NOT_FOUND)) {
                *seqnum = 0;
                return NT_STATUS_OK;
        }
        return status;
}

/**
 * Store the database sequence number inside a transaction.
 */
static NTSTATUS db_ctdb_store_db_seqnum(struct db_ctdb_transaction_handle *h,
                                        uint64_t seqnum)
{
        NTSTATUS status;
        const char *keyname = CTDB_DB_SEQNUM_KEY;
        TDB_DATA key;
        TDB_DATA data;

        key = string_term_tdb_data(keyname);

        data.dptr = (uint8_t *)&seqnum;
        data.dsize = sizeof(uint64_t);

        status = db_ctdb_transaction_store(h, key, data);

        return status;
}

/*
  commit a transaction
 */
static int db_ctdb_transaction_commit(struct db_context *db)
{
        struct db_ctdb_ctx *ctx = talloc_get_type_abort(db->private_data,
                                                        struct db_ctdb_ctx);
        NTSTATUS rets;
        int status;
        struct db_ctdb_transaction_handle *h = ctx->transaction;
        uint64_t old_seqnum, new_seqnum;
        int ret;

        if (h == NULL) {
                DEBUG(0,(__location__ " transaction commit with no open transaction on db 0x%08x\n", ctx->db_id));
                return -1;
        }

        if (h->nested_cancel) {
                db->transaction_cancel(db);
                DEBUG(5,(__location__ " Failed transaction commit after nested cancel\n"));
                return -1;
        }

        if (h->nesting != 0) {
                h->nesting--;
                DEBUG(5, (__location__ " transaction commit on db 0x%08x: nesting %d -> %d\n",
                          ctx->db_id, ctx->transaction->nesting + 1, ctx->transaction->nesting));
                return 0;
        }

        if (h->m_write == NULL) {
                /*
                 * No changes were made, so don't change the seqnum,
                 * don't push to other node, just exit with success.
                 */
                ret = 0;
                goto done;
        }

        DEBUG(5,(__location__ " transaction commit on db 0x%08x\n", ctx->db_id));

        /*
         * As the last db action before committing, bump the database sequence
         * number. Note that this undoes all changes to the seqnum records
         * performed under the transaction. This record is not meant to be
         * modified by user interaction. It is for internal use only...
         */
        rets = db_ctdb_fetch_db_seqnum_from_db(ctx, &old_seqnum);
        if (!NT_STATUS_IS_OK(rets)) {
                DEBUG(1, (__location__ " failed to fetch the db sequence number "
                          "in transaction commit on db 0x%08x\n", ctx->db_id));
                ret = -1;
                goto done;
        }

        new_seqnum = old_seqnum + 1;

        rets = db_ctdb_store_db_seqnum(h, new_seqnum);
        if (!NT_STATUS_IS_OK(rets)) {
                DEBUG(1, (__location__ "failed to store the db sequence number "
                          " in transaction commit on db 0x%08x\n", ctx->db_id));
                ret = -1;
                goto done;
        }

again:
        /* tell ctdbd to commit to the other nodes */
        rets = ctdbd_control_local(messaging_ctdbd_connection(),
                                   CTDB_CONTROL_TRANS3_COMMIT,
                                   h->ctx->db_id, 0,
                                   db_ctdb_marshall_finish(h->m_write),
                                   NULL, NULL, &status);
        if (!NT_STATUS_IS_OK(rets) || status != 0) {
                /*
                 * The TRANS3_COMMIT control should only possibly fail when a
                 * recovery has been running concurrently. In any case, the db
                 * will be the same on all nodes, either the new copy or the
                 * old copy.  This can be detected by comparing the old and new
                 * local sequence numbers.
                 */
                rets = db_ctdb_fetch_db_seqnum_from_db(ctx, &new_seqnum);
                if (!NT_STATUS_IS_OK(rets)) {
                        DEBUG(1, (__location__ " failed to refetch db sequence "
                                  "number after failed TRANS3_COMMIT\n"));
                        ret = -1;
                        goto done;
                }

                if (new_seqnum == old_seqnum) {
                        /* Recovery prevented all our changes: retry. */
                        goto again;
                }
                if (new_seqnum != (old_seqnum + 1)) {
                        DEBUG(0, (__location__ " ERROR: new_seqnum[%lu] != "
                                  "old_seqnum[%lu] + (0 or 1) after failed "
                                  "TRANS3_COMMIT - this should not happen!\n",
                                  (unsigned long)new_seqnum,
                                  (unsigned long)old_seqnum));
                        ret = -1;
                        goto done;
                }
                /*
                 * Recovery propagated our changes to all nodes, completing
                 * our commit for us - succeed.
                 */
        }

        ret = 0;

done:
        h->ctx->transaction = NULL;
        talloc_free(h);
        return ret;
}


/*
  cancel a transaction
 */
static int db_ctdb_transaction_cancel(struct db_context *db)
{
        struct db_ctdb_ctx *ctx = talloc_get_type_abort(db->private_data,
                                                        struct db_ctdb_ctx);
        struct db_ctdb_transaction_handle *h = ctx->transaction;

        if (h == NULL) {
                DEBUG(0,(__location__ " transaction cancel with no open transaction on db 0x%08x\n", ctx->db_id));
                return -1;
        }

        if (h->nesting != 0) {
                h->nesting--;
                h->nested_cancel = true;
                DEBUG(5, (__location__ " transaction cancel on db 0x%08x: nesting %d -> %d\n",
                          ctx->db_id, ctx->transaction->nesting + 1, ctx->transaction->nesting));
                return 0;
        }

        DEBUG(5,(__location__ " Cancel transaction on db 0x%08x\n", ctx->db_id));

        ctx->transaction = NULL;
        talloc_free(h);
        return 0;
}


static NTSTATUS db_ctdb_store(struct db_record *rec, TDB_DATA data, int flag)
{
        struct db_ctdb_rec *crec = talloc_get_type_abort(
                rec->private_data, struct db_ctdb_rec);

        return db_ctdb_ltdb_store(crec->ctdb_ctx, rec->key, &(crec->header), data);
}



#ifdef HAVE_CTDB_CONTROL_SCHEDULE_FOR_DELETION_DECL
static NTSTATUS db_ctdb_send_schedule_for_deletion(struct db_record *rec)
{
        NTSTATUS status;
        struct ctdb_control_schedule_for_deletion *dd;
        TDB_DATA indata;
        int cstatus;
        struct db_ctdb_rec *crec = talloc_get_type_abort(
                rec->private_data, struct db_ctdb_rec);

        indata.dsize = offsetof(struct ctdb_control_schedule_for_deletion, key) + rec->key.dsize;
        indata.dptr = talloc_zero_array(crec, uint8_t, indata.dsize);
        if (indata.dptr == NULL) {
                DEBUG(0, (__location__ " talloc failed!\n"));
                return NT_STATUS_NO_MEMORY;
        }

        dd = (struct ctdb_control_schedule_for_deletion *)(void *)indata.dptr;
        dd->db_id = crec->ctdb_ctx->db_id;
        dd->hdr = crec->header;
        dd->keylen = rec->key.dsize;
        memcpy(dd->key, rec->key.dptr, rec->key.dsize);

        status = ctdbd_control_local(messaging_ctdbd_connection(),
                                     CTDB_CONTROL_SCHEDULE_FOR_DELETION,
                                     crec->ctdb_ctx->db_id,
                                     CTDB_CTRL_FLAG_NOREPLY, /* flags */
                                     indata,
                                     NULL, /* outdata */
                                     NULL, /* errmsg */
                                     &cstatus);
        talloc_free(indata.dptr);

        if (!NT_STATUS_IS_OK(status) || cstatus != 0) {
                DEBUG(1, (__location__ " Error sending local control "
                          "SCHEDULE_FOR_DELETION: %s, cstatus = %d\n",
                          nt_errstr(status), cstatus));
                if (NT_STATUS_IS_OK(status)) {
                        status = NT_STATUS_UNSUCCESSFUL;
                }
        }

        return status;
}
#endif

static NTSTATUS db_ctdb_delete(struct db_record *rec)
{
        NTSTATUS status;

        /*
         * We have to store the header with empty data. TODO: Fix the
         * tdb-level cleanup
         */

        status = db_ctdb_store(rec, tdb_null, 0);
        if (!NT_STATUS_IS_OK(status)) {
                return status;
        }

#ifdef HAVE_CTDB_CONTROL_SCHEDULE_FOR_DELETION_DECL
        status = db_ctdb_send_schedule_for_deletion(rec);
#endif

        return status;
}

static int db_ctdb_record_destr(struct db_record* data)
{
        struct db_ctdb_rec *crec = talloc_get_type_abort(
                data->private_data, struct db_ctdb_rec);
        int threshold;
        int ret;
        struct timeval before;
        double timediff;

        DEBUG(10, (DEBUGLEVEL > 10
                   ? "Unlocking db %u key %s\n"
                   : "Unlocking db %u key %.20s\n",
                   (int)crec->ctdb_ctx->db_id,
                   hex_encode_talloc(data, (unsigned char *)data->key.dptr,
                              data->key.dsize)));

        before = timeval_current();

        ret = tdb_chainunlock(crec->ctdb_ctx->wtdb->tdb, data->key);

        timediff = timeval_elapsed(&before);
        timediff *= 1000;       /* get us milliseconds */

        if (timediff > crec->ctdb_ctx->warn_unlock_msecs) {
                char *key;
                key = hex_encode_talloc(talloc_tos(),
                                        (unsigned char *)data->key.dptr,
                                        data->key.dsize);
                DEBUG(0, ("tdb_chainunlock on db %s, key %s took %f milliseconds\n",
                          tdb_name(crec->ctdb_ctx->wtdb->tdb), key,
                          timediff));
                TALLOC_FREE(key);
        }

        if (ret != 0) {
                DEBUG(0, ("tdb_chainunlock failed\n"));
                return -1;
        }

        threshold = crec->ctdb_ctx->warn_locktime_msecs;
        if (threshold != 0) {
                timediff = timeval_elapsed(&crec->lock_time) * 1000;
                if (timediff > threshold) {
                        const char *key;

                        key = hex_encode_talloc(data,
                                                (unsigned char *)data->key.dptr,
                                                data->key.dsize);
                        DEBUG(0, ("Held tdb lock on db %s, key %s "
                                  "%f milliseconds\n",
                                  tdb_name(crec->ctdb_ctx->wtdb->tdb),
                                  key, timediff));
                }
        }

        return 0;
}

/**
 * Check whether we have a valid local copy of the given record,
 * either for reading or for writing.
 */
static bool db_ctdb_can_use_local_hdr(const struct ctdb_ltdb_header *hdr,
                                      bool read_only)
{
#ifdef HAVE_CTDB_WANT_READONLY_DECL
        if (hdr->dmaster != get_my_vnn()) {
                /* If we're not dmaster, it must be r/o copy. */
                return read_only && (hdr->flags & CTDB_REC_RO_HAVE_READONLY);
        }

        /*
         * If we want write access, no one may have r/o copies.
         */
        return read_only || !(hdr->flags & CTDB_REC_RO_HAVE_DELEGATIONS);
#else
        return (hdr->dmaster == get_my_vnn());
#endif
}

static bool db_ctdb_can_use_local_copy(TDB_DATA ctdb_data, bool read_only)
{
        if (ctdb_data.dptr == NULL) {
                return false;
        }

        if (ctdb_data.dsize < sizeof(struct ctdb_ltdb_header)) {
                return false;
        }

        return db_ctdb_can_use_local_hdr(
                (struct ctdb_ltdb_header *)ctdb_data.dptr, read_only);
}

static struct db_record *fetch_locked_internal(struct db_ctdb_ctx *ctx,
                                               TALLOC_CTX *mem_ctx,
                                               TDB_DATA key,
                                               bool tryonly)
{
        struct db_record *result;
        struct db_ctdb_rec *crec;
        NTSTATUS status;
        TDB_DATA ctdb_data;
        int migrate_attempts;
        struct timeval migrate_start;
        struct timeval chainlock_start;
        struct timeval ctdb_start_time;
        double chainlock_time = 0;
        double ctdb_time = 0;
        int duration_msecs;
        int lockret;

        if (!(result = talloc(mem_ctx, struct db_record))) {
                DEBUG(0, ("talloc failed\n"));
                return NULL;
        }

        if (!(crec = talloc_zero(result, struct db_ctdb_rec))) {
                DEBUG(0, ("talloc failed\n"));
                TALLOC_FREE(result);
                return NULL;
        }

        result->db = ctx->db;
        result->private_data = (void *)crec;
        crec->ctdb_ctx = ctx;

        result->key.dsize = key.dsize;
        result->key.dptr = (uint8_t *)talloc_memdup(result, key.dptr,
                                                    key.dsize);
        if (result->key.dptr == NULL) {
                DEBUG(0, ("talloc failed\n"));
                TALLOC_FREE(result);
                return NULL;
        }

        migrate_attempts = 0;
        GetTimeOfDay(&migrate_start);

        /*
         * Do a blocking lock on the record
         */
again:

        if (DEBUGLEVEL >= 10) {
                char *keystr = hex_encode_talloc(result, key.dptr, key.dsize);
                DEBUG(10, (DEBUGLEVEL > 10
                           ? "Locking db %u key %s\n"
                           : "Locking db %u key %.20s\n",
                           (int)crec->ctdb_ctx->db_id, keystr));
                TALLOC_FREE(keystr);
        }

        GetTimeOfDay(&chainlock_start);
        lockret = tryonly
                ? tdb_chainlock_nonblock(ctx->wtdb->tdb, key)
                : tdb_chainlock(ctx->wtdb->tdb, key);
        chainlock_time += timeval_elapsed(&chainlock_start);

        if (lockret != 0) {
                DEBUG(3, ("tdb_chainlock failed\n"));
                TALLOC_FREE(result);
                return NULL;
        }

        result->store = db_ctdb_store;
        result->delete_rec = db_ctdb_delete;
        talloc_set_destructor(result, db_ctdb_record_destr);

        ctdb_data = tdb_fetch_compat(ctx->wtdb->tdb, key);

        /*
         * See if we have a valid record and we are the dmaster. If so, we can
         * take the shortcut and just return it.
         */

        if (!db_ctdb_can_use_local_copy(ctdb_data, false)) {
                SAFE_FREE(ctdb_data.dptr);
                tdb_chainunlock(ctx->wtdb->tdb, key);
                talloc_set_destructor(result, NULL);

                if (tryonly && (migrate_attempts != 0)) {
                        DEBUG(5, ("record migrated away again\n"));
                        TALLOC_FREE(result);
                        return NULL;
                }

                migrate_attempts += 1;

                DEBUG(10, ("ctdb_data.dptr = %p, dmaster = %u (%u) %u\n",
                           ctdb_data.dptr, ctdb_data.dptr ?
                           ((struct ctdb_ltdb_header *)ctdb_data.dptr)->dmaster : -1,
                           get_my_vnn(),
                           ctdb_data.dptr ?
                           ((struct ctdb_ltdb_header *)ctdb_data.dptr)->flags : 0));

                GetTimeOfDay(&ctdb_start_time);
                status = ctdbd_migrate(messaging_ctdbd_connection(), ctx->db_id,
                                       key);
                ctdb_time += timeval_elapsed(&ctdb_start_time);

                if (!NT_STATUS_IS_OK(status)) {
                        DEBUG(5, ("ctdb_migrate failed: %s\n",
                                  nt_errstr(status)));
                        TALLOC_FREE(result);
                        return NULL;
                }
                /* now its migrated, try again */
                goto again;
        }

        {
                double duration;
                duration = timeval_elapsed(&migrate_start);

                /*
                 * Convert the duration to milliseconds to avoid a
                 * floating-point division of
                 * lp_parm_int("migrate_duration") by 1000.
                 */
                duration_msecs = duration * 1000;
        }

        if ((migrate_attempts > ctx->warn_migrate_attempts) ||
            (duration_msecs > ctx->warn_migrate_msecs)) {
                int chain = 0;

                if (tdb_get_flags(ctx->wtdb->tdb) & TDB_INCOMPATIBLE_HASH) {
                        chain = tdb_jenkins_hash(&key) %
                                tdb_hash_size(ctx->wtdb->tdb);
                }

                DEBUG(0, ("db_ctdb_fetch_locked for %s key %s, chain %d "
                          "needed %d attempts, %d milliseconds, "
                          "chainlock: %d ms, CTDB %d ms\n",
                          tdb_name(ctx->wtdb->tdb),
                          hex_encode_talloc(talloc_tos(),
                                            (unsigned char *)key.dptr,
                                            key.dsize),
                          chain,
                          migrate_attempts, duration_msecs,
                          (int) chainlock_time * 1000,
                          (int) ctdb_time * 1000));
        }

        GetTimeOfDay(&crec->lock_time);

        memcpy(&crec->header, ctdb_data.dptr, sizeof(crec->header));

        result->value.dsize = ctdb_data.dsize - sizeof(crec->header);
        result->value.dptr = NULL;

        if ((result->value.dsize != 0)
            && !(result->value.dptr = (uint8_t *)talloc_memdup(
                         result, ctdb_data.dptr + sizeof(crec->header),
                         result->value.dsize))) {
                DEBUG(0, ("talloc failed\n"));
                TALLOC_FREE(result);
        }

        SAFE_FREE(ctdb_data.dptr);

        return result;
}

static struct db_record *db_ctdb_fetch_locked(struct db_context *db,
                                              TALLOC_CTX *mem_ctx,
                                              TDB_DATA key)
{
        struct db_ctdb_ctx *ctx = talloc_get_type_abort(db->private_data,
                                                        struct db_ctdb_ctx);

        if (ctx->transaction != NULL) {
                return db_ctdb_fetch_locked_transaction(ctx, mem_ctx, key);
        }

        if (db->persistent) {
                return db_ctdb_fetch_locked_persistent(ctx, mem_ctx, key);
        }

        return fetch_locked_internal(ctx, mem_ctx, key, false);
}

static struct db_record *db_ctdb_try_fetch_locked(struct db_context *db,
                                                  TALLOC_CTX *mem_ctx,
                                                  TDB_DATA key)
{
        struct db_ctdb_ctx *ctx = talloc_get_type_abort(db->private_data,
                                                        struct db_ctdb_ctx);

        if (ctx->transaction != NULL) {
                return db_ctdb_fetch_locked_transaction(ctx, mem_ctx, key);
        }

        if (db->persistent) {
                return db_ctdb_fetch_locked_persistent(ctx, mem_ctx, key);
        }

        return fetch_locked_internal(ctx, mem_ctx, key, true);
}

struct db_ctdb_parse_record_state {
        void (*parser)(TDB_DATA key, TDB_DATA data, void *private_data);
        void *private_data;
        bool ask_for_readonly_copy;
        bool done;
};

static void db_ctdb_parse_record_parser(
        TDB_DATA key, struct ctdb_ltdb_header *header,
        TDB_DATA data, void *private_data)
{
        struct db_ctdb_parse_record_state *state =
                (struct db_ctdb_parse_record_state *)private_data;
        state->parser(key, data, state->private_data);
}

static void db_ctdb_parse_record_parser_nonpersistent(
        TDB_DATA key, struct ctdb_ltdb_header *header,
        TDB_DATA data, void *private_data)
{
        struct db_ctdb_parse_record_state *state =
                (struct db_ctdb_parse_record_state *)private_data;

        if (db_ctdb_can_use_local_hdr(header, true)) {
                state->parser(key, data, state->private_data);
                state->done = true;
        } else {
                /*
                 * We found something in the db, so it seems that this record,
                 * while not usable locally right now, is popular. Ask for a
                 * R/O copy.
                 */
                state->ask_for_readonly_copy = true;
        }
}

static NTSTATUS db_ctdb_parse_record(struct db_context *db, TDB_DATA key,
                                     void (*parser)(TDB_DATA key,
                                                    TDB_DATA data,
                                                    void *private_data),
                                     void *private_data)
{
        struct db_ctdb_ctx *ctx = talloc_get_type_abort(
                db->private_data, struct db_ctdb_ctx);
        struct db_ctdb_parse_record_state state;
        NTSTATUS status;

        state.parser = parser;
        state.private_data = private_data;

        if (ctx->transaction != NULL) {
                struct db_ctdb_transaction_handle *h = ctx->transaction;
                bool found;

                /*
                 * Transactions only happen for persistent db's.
                 */

                found = parse_newest_in_marshall_buffer(
                        h->m_write, key, db_ctdb_parse_record_parser, &state);

                if (found) {
                        return NT_STATUS_OK;
                }
        }

        if (db->persistent) {
                /*
                 * Persistent db, but not found in the transaction buffer
                 */
                return db_ctdb_ltdb_parse(
                        ctx, key, db_ctdb_parse_record_parser, &state);
        }

        state.done = false;
        state.ask_for_readonly_copy = false;

        status = db_ctdb_ltdb_parse(
                ctx, key, db_ctdb_parse_record_parser_nonpersistent, &state);
        if (NT_STATUS_IS_OK(status) && state.done) {
                return NT_STATUS_OK;
        }

        return ctdbd_parse(messaging_ctdbd_connection(), ctx->db_id, key,
                           state.ask_for_readonly_copy, parser, private_data);
}

struct traverse_state {
        struct db_context *db;
        int (*fn)(struct db_record *rec, void *private_data);
        void *private_data;
        int count;
};

static void traverse_callback(TDB_DATA key, TDB_DATA data, void *private_data)
{
        struct traverse_state *state = (struct traverse_state *)private_data;
        struct db_record *rec;
        TALLOC_CTX *tmp_ctx = talloc_new(state->db);
        /* we have to give them a locked record to prevent races */
        rec = db_ctdb_fetch_locked(state->db, tmp_ctx, key);
        if (rec && rec->value.dsize > 0) {
                state->fn(rec, state->private_data);
        }
        talloc_free(tmp_ctx);
}

static int traverse_persistent_callback(TDB_CONTEXT *tdb, TDB_DATA kbuf, TDB_DATA dbuf,
                                        void *private_data)
{
        struct traverse_state *state = (struct traverse_state *)private_data;
        struct db_record *rec;
        TALLOC_CTX *tmp_ctx = talloc_new(state->db);
        int ret = 0;

        /*
         * Skip the __db_sequence_number__ key:
         * This is used for persistent transactions internally.
         */
        if (kbuf.dsize == strlen(CTDB_DB_SEQNUM_KEY) + 1 &&
            strcmp((const char*)kbuf.dptr, CTDB_DB_SEQNUM_KEY) == 0)
        {
                goto done;
        }

        /* we have to give them a locked record to prevent races */
        rec = db_ctdb_fetch_locked(state->db, tmp_ctx, kbuf);
        if (rec && rec->value.dsize > 0) {
                ret = state->fn(rec, state->private_data);
        }

done:
        talloc_free(tmp_ctx);
        return ret;
}

/* wrapper to use traverse_persistent_callback with dbwrap */
static int traverse_persistent_callback_dbwrap(struct db_record *rec, void* data)
{
        return traverse_persistent_callback(NULL, rec->key, rec->value, data);
}


static int db_ctdb_traverse(struct db_context *db,
                            int (*fn)(struct db_record *rec,
                                      void *private_data),
                            void *private_data)
{
        NTSTATUS status;
        struct db_ctdb_ctx *ctx = talloc_get_type_abort(db->private_data,
                                                        struct db_ctdb_ctx);
        struct traverse_state state;

        state.db = db;
        state.fn = fn;
        state.private_data = private_data;
        state.count = 0;

        if (db->persistent) {
                struct tdb_context *ltdb = ctx->wtdb->tdb;
                int ret;

                /* for persistent databases we don't need to do a ctdb traverse,
                   we can do a faster local traverse */
                ret = tdb_traverse(ltdb, traverse_persistent_callback, &state);
                if (ret < 0) {
                        return ret;
                }
                if (ctx->transaction && ctx->transaction->m_write) {
                        /*
                         * we now have to handle keys not yet
                         * present at transaction start
                         */
                        struct db_context *newkeys = db_open_rbt(talloc_tos());
                        struct ctdb_marshall_buffer *mbuf = ctx->transaction->m_write;
                        struct ctdb_rec_data *rec=NULL;
                        int i;
                        int count = 0;

                        if (newkeys == NULL) {
                                return -1;
                        }

                        for (i=0; i<mbuf->count; i++) {
                                TDB_DATA key;
                                rec = db_ctdb_marshall_loop_next_key(
                                        mbuf, rec, &key);
                                SMB_ASSERT(rec != NULL);

                                if (!tdb_exists(ltdb, key)) {
                                        dbwrap_store(newkeys, key, tdb_null, 0);
                                }
                        }
                        status = dbwrap_traverse(newkeys,
                                                 traverse_persistent_callback_dbwrap,
                                                 &state,
                                                 &count);
                        talloc_free(newkeys);
                        if (!NT_STATUS_IS_OK(status)) {
                                return -1;
                        }
                        ret += count;
                }
                return ret;
        }

        status = ctdbd_traverse(ctx->db_id, traverse_callback, &state);
        if (!NT_STATUS_IS_OK(status)) {
                return -1;
        }
        return state.count;
}

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

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

static void traverse_read_callback(TDB_DATA key, TDB_DATA data, void *private_data)
{
        struct traverse_state *state = (struct traverse_state *)private_data;
        struct db_record rec;

        ZERO_STRUCT(rec);
        rec.db = state->db;
        rec.key = key;
        rec.value = data;
        rec.store = db_ctdb_store_deny;
        rec.delete_rec = db_ctdb_delete_deny;
        rec.private_data = NULL;
        state->fn(&rec, state->private_data);
        state->count++;
}

static int traverse_persistent_callback_read(TDB_CONTEXT *tdb, TDB_DATA kbuf, TDB_DATA dbuf,
                                        void *private_data)
{
        struct traverse_state *state = (struct traverse_state *)private_data;
        struct db_record rec;

        /*
         * Skip the __db_sequence_number__ key:
         * This is used for persistent transactions internally.
         */
        if (kbuf.dsize == strlen(CTDB_DB_SEQNUM_KEY) + 1 &&
            strcmp((const char*)kbuf.dptr, CTDB_DB_SEQNUM_KEY) == 0)
        {
                return 0;
        }

        ZERO_STRUCT(rec);
        rec.db = state->db;
        rec.key = kbuf;
        rec.value = dbuf;
        rec.store = db_ctdb_store_deny;
        rec.delete_rec = db_ctdb_delete_deny;
        rec.private_data = NULL;

        if (rec.value.dsize <= sizeof(struct ctdb_ltdb_header)) {
                /* a deleted record */
                return 0;
        }
        rec.value.dsize -= sizeof(struct ctdb_ltdb_header);
        rec.value.dptr += sizeof(struct ctdb_ltdb_header);

        state->count++;
        return state->fn(&rec, state->private_data);
}

static int db_ctdb_traverse_read(struct db_context *db,
                                 int (*fn)(struct db_record *rec,
                                           void *private_data),
                                 void *private_data)
{
        NTSTATUS status;
        struct db_ctdb_ctx *ctx = talloc_get_type_abort(db->private_data,
                                                        struct db_ctdb_ctx);
        struct traverse_state state;

        state.db = db;
        state.fn = fn;
        state.private_data = private_data;
        state.count = 0;

        if (db->persistent) {
                /* for persistent databases we don't need to do a ctdb traverse,
                   we can do a faster local traverse */
                return tdb_traverse_read(ctx->wtdb->tdb, traverse_persistent_callback_read, &state);
        }

        status = ctdbd_traverse(ctx->db_id, traverse_read_callback, &state);
        if (!NT_STATUS_IS_OK(status)) {
                return -1;
        }
        return state.count;
}

static int db_ctdb_get_seqnum(struct db_context *db)
{
        struct db_ctdb_ctx *ctx = talloc_get_type_abort(db->private_data,
                                                        struct db_ctdb_ctx);
        return tdb_get_seqnum(ctx->wtdb->tdb);
}

static void db_ctdb_id(struct db_context *db, const uint8_t **id,
                       size_t *idlen)
{
        struct db_ctdb_ctx *ctx = talloc_get_type_abort(
                db->private_data, struct db_ctdb_ctx);

        *id = (uint8_t *)&ctx->db_id;
        *idlen = sizeof(ctx->db_id);
}

struct db_context *db_open_ctdb(TALLOC_CTX *mem_ctx,
                                const char *name,
                                int hash_size, int tdb_flags,
                                int open_flags, mode_t mode,
                                enum dbwrap_lock_order lock_order,
                                uint64_t dbwrap_flags)
{
        struct db_context *result;
        struct db_ctdb_ctx *db_ctdb;
        char *db_path;
        struct ctdbd_connection *conn;
        struct loadparm_context *lp_ctx;
        struct ctdb_db_priority prio;
        NTSTATUS status;
        int cstatus;

        if (!lp_clustering()) {
                DEBUG(10, ("Clustering disabled -- no ctdb\n"));
                return NULL;
        }

        if (!(result = talloc_zero(mem_ctx, struct db_context))) {
                DEBUG(0, ("talloc failed\n"));
                TALLOC_FREE(result);
                return NULL;
        }

        if (!(db_ctdb = talloc(result, struct db_ctdb_ctx))) {
                DEBUG(0, ("talloc failed\n"));
                TALLOC_FREE(result);
                return NULL;
        }

        result->name = talloc_strdup(result, name);
        if (result->name == NULL) {
                DEBUG(0, ("talloc failed\n"));
                TALLOC_FREE(result);
                return NULL;
        }

        db_ctdb->transaction = NULL;
        db_ctdb->db = result;

        conn = messaging_ctdbd_connection();
        if (conn == NULL) {
                DEBUG(1, ("Could not connect to ctdb\n"));
                TALLOC_FREE(result);
                return NULL;
        }

        if (!NT_STATUS_IS_OK(ctdbd_db_attach(conn, name, &db_ctdb->db_id, tdb_flags))) {
                DEBUG(0, ("ctdbd_db_attach failed for %s\n", name));
                TALLOC_FREE(result);
                return NULL;
        }

        db_path = ctdbd_dbpath(conn, db_ctdb, db_ctdb->db_id);

        result->persistent = ((tdb_flags & TDB_CLEAR_IF_FIRST) == 0);
        result->lock_order = lock_order;

        /* only pass through specific flags */
        tdb_flags &= TDB_SEQNUM;

        /* honor permissions if user has specified O_CREAT */
        if (open_flags & O_CREAT) {
                chmod(db_path, mode);
        }

        prio.db_id = db_ctdb->db_id;
        prio.priority = lock_order;

        status = ctdbd_control_local(
                conn, CTDB_CONTROL_SET_DB_PRIORITY, 0, 0,
                make_tdb_data((uint8_t *)&prio, sizeof(prio)),
                NULL, NULL, &cstatus);

        if (!NT_STATUS_IS_OK(status) || (cstatus != 0)) {
                DEBUG(1, ("CTDB_CONTROL_SET_DB_PRIORITY failed: %s, %d\n",
                          nt_errstr(status), cstatus));
                TALLOC_FREE(result);
                return NULL;
        }

#ifdef HAVE_CTDB_WANT_READONLY_DECL
        if (!result->persistent &&
            (dbwrap_flags & DBWRAP_FLAG_OPTIMIZE_READONLY_ACCESS))
        {
                TDB_DATA indata;

                indata = make_tdb_data((uint8_t *)&db_ctdb->db_id,
                                       sizeof(db_ctdb->db_id));

                status = ctdbd_control_local(
                        conn, CTDB_CONTROL_SET_DB_READONLY, 0, 0, indata,
                        NULL, NULL, &cstatus);
                if (!NT_STATUS_IS_OK(status) || (cstatus != 0)) {
                        DEBUG(1, ("CTDB_CONTROL_SET_DB_READONLY failed: "
                                  "%s, %d\n", nt_errstr(status), cstatus));
                        TALLOC_FREE(result);
                        return NULL;
                }
        }
#endif

        lp_ctx = loadparm_init_s3(db_path, loadparm_s3_helpers());

        db_ctdb->wtdb = tdb_wrap_open(db_ctdb, db_path, hash_size, tdb_flags,
                                      O_RDWR, 0, lp_ctx);
        talloc_unlink(db_path, lp_ctx);
        if (db_ctdb->wtdb == NULL) {
                DEBUG(0, ("Could not open tdb %s: %s\n", db_path, strerror(errno)));
                TALLOC_FREE(result);
                return NULL;
        }
        talloc_free(db_path);

        if (result->persistent) {
                db_ctdb->lock_ctx = g_lock_ctx_init(db_ctdb,
                                                    ctdb_conn_msg_ctx(conn));
                if (db_ctdb->lock_ctx == NULL) {
                        DEBUG(0, ("g_lock_ctx_init failed\n"));
                        TALLOC_FREE(result);
                        return NULL;
                }
        }

        db_ctdb->warn_unlock_msecs = lp_parm_int(-1, "ctdb",
                                                 "unlock_warn_threshold", 5);
        db_ctdb->warn_migrate_attempts = lp_parm_int(-1, "ctdb",
                                                     "migrate_attempts", 10);
        db_ctdb->warn_migrate_msecs = lp_parm_int(-1, "ctdb",
                                                  "migrate_duration", 5000);
        db_ctdb->warn_locktime_msecs = lp_ctdb_locktime_warn_threshold();

        result->private_data = (void *)db_ctdb;
        result->fetch_locked = db_ctdb_fetch_locked;
        result->try_fetch_locked = db_ctdb_try_fetch_locked;
        result->parse_record = db_ctdb_parse_record;
        result->traverse = db_ctdb_traverse;
        result->traverse_read = db_ctdb_traverse_read;
        result->get_seqnum = db_ctdb_get_seqnum;
        result->transaction_start = db_ctdb_transaction_start;
        result->transaction_commit = db_ctdb_transaction_commit;
        result->transaction_cancel = db_ctdb_transaction_cancel;
        result->id = db_ctdb_id;
        result->stored_callback = NULL;

        DEBUG(3,("db_open_ctdb: opened database '%s' with dbid 0x%x\n",
                 name, db_ctdb->db_id));

        return result;
}

#else /* CLUSTER_SUPPORT */

struct db_context *db_open_ctdb(TALLOC_CTX *mem_ctx,
                                const char *name,
                                int hash_size, int tdb_flags,
                                int open_flags, mode_t mode,
                                enum dbwrap_lock_order lock_order,
                                uint64_t dbwrap_flags)
{
        DEBUG(3, ("db_open_ctdb: no cluster support!\n"));
        errno = ENOSYS;
        return NULL;
}

#endif