s3:smbXsrv_client: only change the dbwrap_watch instance when the record has changed

This will become important in the following commits when the
dbwrap_watch layer will only wake up one watcher at a time
and each woken watcher will wakeup the next one.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15125

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>

diff --git a/source3/smbd/smbXsrv_client.c b/source3/smbd/smbXsrv_client.c
index 93eef753b62259431948c6c9912097a1544893f3..079ca80ad121b4208d88b7a59909dde6da69be05 100644 (file)
--- a/source3/smbd/smbXsrv_client.c
+++ b/source3/smbd/smbXsrv_client.c
@@ -189,7 +189,8 @@ static void smbXsrv_client_global_verify_record(struct db_record *db_rec,
                                        bool *is_free,
                                        bool *was_free,
                                        TALLOC_CTX *mem_ctx,
-                                       struct smbXsrv_client_global0 **_g)
+                                       struct smbXsrv_client_global0 **_g,
+                                       uint32_t *pseqnum)
 {
        TDB_DATA key;
        TDB_DATA val;
@@ -208,6 +209,9 @@ static void smbXsrv_client_global_verify_record(struct db_record *db_rec,
        if (_g) {
                *_g = NULL;
        }
+       if (pseqnum) {
+               *pseqnum = 0;
+       }
 
        key = dbwrap_record_get_key(db_rec);
 
@@ -270,6 +274,9 @@ static void smbXsrv_client_global_verify_record(struct db_record *db_rec,
        if (_g) {
                *_g = talloc_move(mem_ctx, &global);
        }
+       if (pseqnum) {
+               *pseqnum = global_blob.seqnum;
+       }
        TALLOC_FREE(frame);
 }
 
@@ -414,6 +421,8 @@ struct smb2srv_client_mc_negprot_state {
        struct tevent_context *ev;
        struct smbd_smb2_request *smb2req;
        struct db_record *db_rec;
+       uint64_t watch_instance;
+       uint32_t last_seqnum;
 };
 
 static void smb2srv_client_mc_negprot_cleanup(struct tevent_req *req,
@@ -423,7 +432,12 @@ static void smb2srv_client_mc_negprot_cleanup(struct tevent_req *req,
                tevent_req_data(req,
                struct smb2srv_client_mc_negprot_state);
 
-       TALLOC_FREE(state->db_rec);
+       if (state->db_rec != NULL) {
+               dbwrap_watched_watch_remove_instance(state->db_rec,
+                                                    state->watch_instance);
+               state->watch_instance = 0;
+               TALLOC_FREE(state->db_rec);
+       }
 }
 
 static void smb2srv_client_mc_negprot_next(struct tevent_req *req);
@@ -470,6 +484,7 @@ static void smb2srv_client_mc_negprot_next(struct tevent_req *req)
        bool is_free = false;
        struct tevent_req *subreq = NULL;
        NTSTATUS status;
+       uint32_t seqnum = 0;
 
        SMB_ASSERT(state->db_rec == NULL);
        state->db_rec = smbXsrv_client_global_fetch_locked(table->global.db_ctx,
@@ -484,8 +499,13 @@ static void smb2srv_client_mc_negprot_next(struct tevent_req *req)
                                            &is_free,
                                            NULL,
                                            state,
-                                           &global);
+                                           &global,
+                                           &seqnum);
        if (is_free) {
+               dbwrap_watched_watch_remove_instance(state->db_rec,
+                                                    state->watch_instance);
+               state->watch_instance = 0;
+
                /*
                 * This stores the new client information in
                 * smbXsrv_client_global.tdb
@@ -542,10 +562,31 @@ static void smb2srv_client_mc_negprot_next(struct tevent_req *req)
        }
        tevent_req_set_callback(subreq, smb2srv_client_mc_negprot_done, req);
 
+       /*
+        * If the record changed, but we are not happy with the change yet,
+        * we better remove ourself from the waiter list
+        * (most likely the first position)
+        * and re-add us at the end of the list.
+        *
+        * This gives other waiters a change
+        * to make progress.
+        *
+        * Otherwise we'll keep our waiter instance alive,
+        * keep waiting (most likely at first position).
+        * It means the order of watchers stays fair.
+        */
+       if (state->last_seqnum != seqnum) {
+               state->last_seqnum = seqnum;
+               dbwrap_watched_watch_remove_instance(state->db_rec,
+                                                    state->watch_instance);
+               state->watch_instance =
+                       dbwrap_watched_watch_add_instance(state->db_rec);
+       }
+
        subreq = dbwrap_watched_watch_send(state,
                                           state->ev,
                                           state->db_rec,
-                                          0, /* resume_instance */
+                                          state->watch_instance,
                                           global->server_id);
        if (tevent_req_nomem(subreq, req)) {
                return;
@@ -674,14 +715,20 @@ static void smb2srv_client_mc_negprot_watched(struct tevent_req *subreq)
        struct tevent_req *req =
                tevent_req_callback_data(subreq,
                struct tevent_req);
+       struct smb2srv_client_mc_negprot_state *state =
+               tevent_req_data(req,
+               struct smb2srv_client_mc_negprot_state);
        NTSTATUS status;
+       uint64_t instance = 0;
 
-       status = dbwrap_watched_watch_recv(subreq, NULL, NULL, NULL);
+       status = dbwrap_watched_watch_recv(subreq, &instance, NULL, NULL);
        TALLOC_FREE(subreq);
        if (tevent_req_nterror(req, status)) {
                return;
        }
 
+       state->watch_instance = instance;
+
        smb2srv_client_mc_negprot_next(req);
 }