mgmtd, vtysh: fix possible conflict when reading the config

When FRR starts, after mgmtd is initialized, backend clients connect to
it and request their config. To supply the config, mgmtd creates a
configuration transaction. At the same time, `vtysh -b` tries to read
the startup config and configure mgmtd, which also creates a
configuration transaction. If these two actions happen at the exact same
time, there's a conflict between them, because only a single
configuration translaction is allowed. Because of that, vtysh fails and
the config is completely ignored.

When starting the config reading, vtysh locks candidate and running
datastores in mgmtd. This commit adds locking of running datastore when
initializing the backend client. It allows to retry locking on the vtysh
side and read the config only when the lock is aquired instead of
failing.

This change also prevents running datastore from being changed during
initialization of backend clients. This could lead to a desynchronized
state between mgmtd and backends.

Signed-off-by: Igor Ryzhov <iryzhov@nfware.com>

1 files changed, 25 insertions, 3 deletions

diff --git a/mgmtd/mgmt_txn.c b/mgmtd/mgmt_txn.c
index df2a1d852d..664f42f4ba 100644
--- a/mgmtd/mgmt_txn.c
+++ b/mgmtd/mgmt_txn.c
@@ -105,6 +105,7 @@ struct mgmt_commit_cfg_req {
 	uint8_t abort : 1;
 	uint8_t implicit : 1;
 	uint8_t rollback : 1;
+	uint8_t init : 1;
 
 	/* Track commit phases */
 	enum mgmt_commit_phase phase;
@@ -750,6 +751,14 @@ static int mgmt_txn_send_commit_cfg_reply(struct mgmt_txn_ctx *txn,
 		mgmt_history_rollback_complete(success);
 	}
 
+	if (txn->commit_cfg_req->req.commit_cfg.init) {
+		/*
+		 * This is the backend init request.
+		 * We need to unlock the running datastore.
+		 */
+		mgmt_ds_unlock(txn->commit_cfg_req->req.commit_cfg.dst_ds_ctx);
+	}
+
 	txn->commit_cfg_req->req.commit_cfg.cmt_stats = NULL;
 	mgmt_txn_req_free(&txn->commit_cfg_req);
 
@@ -2081,15 +2090,26 @@ int mgmt_txn_notify_be_adapter_conn(struct mgmt_be_client_adapter *adapter,
 	struct mgmt_commit_cfg_req *cmtcfg_req;
 	static struct mgmt_commit_stats dummy_stats;
 	struct nb_config_cbs *adapter_cfgs = NULL;
+	struct mgmt_ds_ctx *ds_ctx;
 
 	memset(&dummy_stats, 0, sizeof(dummy_stats));
 	if (connect) {
-		/* Get config for this single backend client */
+		ds_ctx = mgmt_ds_get_ctx_by_id(mm, MGMTD_DS_RUNNING);
+		assert(ds_ctx);
+
+		/*
+		 * Lock the running datastore to prevent any changes while we
+		 * are initializing the backend.
+		 */
+		if (mgmt_ds_lock(ds_ctx, 0) != 0)
+			return -1;
 
+		/* Get config for this single backend client */
 		mgmt_be_get_adapter_config(adapter, &adapter_cfgs);
 		if (!adapter_cfgs || RB_EMPTY(nb_config_cbs, adapter_cfgs)) {
 			SET_FLAG(adapter->flags,
 				 MGMTD_BE_ADAPTER_FLAGS_CFG_SYNCED);
+			mgmt_ds_unlock(ds_ctx);
 			return 0;
 		}
 
@@ -2101,6 +2121,7 @@ int mgmt_txn_notify_be_adapter_conn(struct mgmt_be_client_adapter *adapter,
 		if (!txn) {
 			__log_err("Failed to create CONFIG Transaction for downloading CONFIGs for client '%s'",
 				  adapter->name);
+			mgmt_ds_unlock(ds_ctx);
 			nb_config_diff_del_changes(adapter_cfgs);
 			return -1;
 		}
@@ -2114,10 +2135,11 @@ int mgmt_txn_notify_be_adapter_conn(struct mgmt_be_client_adapter *adapter,
 		txn_req = mgmt_txn_req_alloc(txn, 0, MGMTD_TXN_PROC_COMMITCFG);
 		txn_req->req.commit_cfg.src_ds_id = MGMTD_DS_NONE;
 		txn_req->req.commit_cfg.src_ds_ctx = 0;
-		txn_req->req.commit_cfg.dst_ds_id = MGMTD_DS_NONE;
-		txn_req->req.commit_cfg.dst_ds_ctx = 0;
+		txn_req->req.commit_cfg.dst_ds_id = MGMTD_DS_RUNNING;
+		txn_req->req.commit_cfg.dst_ds_ctx = ds_ctx;
 		txn_req->req.commit_cfg.validate_only = false;
 		txn_req->req.commit_cfg.abort = false;
+		txn_req->req.commit_cfg.init = true;
 		txn_req->req.commit_cfg.cmt_stats = &dummy_stats;
 		txn_req->req.commit_cfg.cfg_chgs = adapter_cfgs;