s3:smbXsrv_session: 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_session.c b/source3/smbd/smbXsrv_session.c
index 05b382ce506ff1b773f0705c577696447d8e0fcb..59c6b49f2d99058a2100491b896e081f256e80d9 100644 (file)
--- a/source3/smbd/smbXsrv_session.c
+++ b/source3/smbd/smbXsrv_session.c
@@ -709,7 +709,8 @@ static void smbXsrv_session_global_verify_record(struct db_record *db_rec,
                                        bool *is_free,
                                        bool *was_free,
                                        TALLOC_CTX *mem_ctx,
-                                       struct smbXsrv_session_global0 **_g);
+                                       struct smbXsrv_session_global0 **_g,
+                                       uint32_t *pseqnum);
 
 static NTSTATUS smbXsrv_session_global_allocate(struct db_context *db,
                                        TALLOC_CTX *mem_ctx,
@@ -761,7 +762,7 @@ static NTSTATUS smbXsrv_session_global_allocate(struct db_context *db,
                smbXsrv_session_global_verify_record(global->db_rec,
                                                     &is_free,
                                                     &was_free,
-                                                    NULL, NULL);
+                                                    NULL, NULL, NULL);
 
                if (!is_free) {
                        TALLOC_FREE(global->db_rec);
@@ -801,7 +802,8 @@ static void smbXsrv_session_global_verify_record(struct db_record *db_rec,
                                        bool *is_free,
                                        bool *was_free,
                                        TALLOC_CTX *mem_ctx,
-                                       struct smbXsrv_session_global0 **_g)
+                                       struct smbXsrv_session_global0 **_g,
+                                       uint32_t *pseqnum)
 {
        TDB_DATA key;
        TDB_DATA val;
@@ -820,6 +822,9 @@ static void smbXsrv_session_global_verify_record(struct db_record *db_rec,
        if (_g) {
                *_g = NULL;
        }
+       if (pseqnum) {
+               *pseqnum = 0;
+       }
 
        key = dbwrap_record_get_key(db_rec);
 
@@ -909,6 +914,9 @@ static void smbXsrv_session_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);
 }
 
@@ -981,6 +989,8 @@ struct smb2srv_session_close_previous_state {
        uint64_t previous_session_id;
        uint64_t current_session_id;
        struct db_record *db_rec;
+       uint64_t watch_instance;
+       uint32_t last_seqnum;
 };
 
 static void smb2srv_session_close_previous_cleanup(struct tevent_req *req,
@@ -990,7 +1000,12 @@ static void smb2srv_session_close_previous_cleanup(struct tevent_req *req,
                tevent_req_data(req,
                struct smb2srv_session_close_previous_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_session_close_previous_check(struct tevent_req *req);
@@ -1080,12 +1095,14 @@ static void smb2srv_session_close_previous_check(struct tevent_req *req)
        struct tevent_req *subreq = NULL;
        NTSTATUS status;
        bool is_free = false;
+       uint32_t seqnum = 0;
 
        smbXsrv_session_global_verify_record(state->db_rec,
                                             &is_free,
                                             NULL,
                                             state,
-                                            &global);
+                                            &global,
+                                            &seqnum);
 
        if (is_free) {
                tevent_req_done(req);
@@ -1104,8 +1121,29 @@ static void smb2srv_session_close_previous_check(struct tevent_req *req)
                return;
        }
 
+       /*
+        * 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,
                                           (struct server_id){0});
        if (tevent_req_nomem(subreq, req)) {
                return;
@@ -1158,13 +1196,16 @@ static void smb2srv_session_close_previous_modified(struct tevent_req *subreq)
                struct smb2srv_session_close_previous_state);
        uint32_t global_id;
        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;
+
        global_id = state->previous_session_id & UINT32_MAX;
 
        state->db_rec = smbXsrv_session_global_fetch_locked(
@@ -2323,7 +2364,8 @@ NTSTATUS smb2srv_session_lookup_global(struct smbXsrv_client *client,
                                             &is_free,
                                             NULL,
                                             session,
-                                            &session->global);
+                                            &session->global,
+                                            NULL);
        if (is_free) {
                TALLOC_FREE(frame);
                return NT_STATUS_USER_SESSION_DELETED;