Generate RDB with Functions only via redis-cli --functions-rdb (#9968)

This is needed in order to ease the deployment of functions for ephemeral cases, where user
needs to spin up a server with functions pre-loaded.

#### Details:

* Added `--functions-rdb` option to _redis-cli_.
* Functions only rdb via `REPLCONF rdb-filter-only functions`. This is a placeholder for a space
  separated inclusion filter for the RDB. In the future can be `REPLCONF rdb-filter-only
  "functions db:3 key-patten:user*"` and a complementing `rdb-filter-exclude` `REPLCONF`
  can also be added.
* Handle "slave requirements" specification to RDB saving code so we can use the same RDB
  when different slaves express the same requirements (like functions-only) and not share the
  RDB when their requirements differ. This is currently just a flags `int`, but can be extended to
  a more complex structure with various filter fields.
* make sure to support filters only in diskless replication mode (not to override the persistence file),
  we do that by forcing diskless (even if disabled by config)

other changes:
* some refactoring in rdb.c (extract portion of a big function to a sub-function)
* rdb_key_save_delay used in AOFRW too
* sendChildInfo takes the number of updated keys (incremental, rather than absolute)

Co-authored-by: Oran Agra <oran@redislabs.com>

1 files changed, 3 insertions, 3 deletions

diff --git a/src/server.c b/src/server.c
index 6d531449e..a5a95d1d8 100644
--- a/src/server.c
+++ b/src/server.c
@@ -1209,7 +1209,7 @@ int serverCron(struct aeEventLoop *eventLoop, long long id, void *clientData) {
                     sp->changes, (int)sp->seconds);
                 rdbSaveInfo rsi, *rsiptr;
                 rsiptr = rdbPopulateSaveInfo(&rsi);
-                rdbSaveBackground(server.rdb_filename,rsiptr);
+                rdbSaveBackground(SLAVE_REQ_NONE, server.rdb_filename,rsiptr);
                 break;
             }
         }
@@ -1298,7 +1298,7 @@ int serverCron(struct aeEventLoop *eventLoop, long long id, void *clientData) {
     {
         rdbSaveInfo rsi, *rsiptr;
         rsiptr = rdbPopulateSaveInfo(&rsi);
-        if (rdbSaveBackground(server.rdb_filename,rsiptr) == C_OK)
+        if (rdbSaveBackground(SLAVE_REQ_NONE, server.rdb_filename,rsiptr) == C_OK)
             server.rdb_bgsave_scheduled = 0;
     }
 
@@ -3692,7 +3692,7 @@ int prepareForShutdown(int flags) {
         /* Snapshotting. Perform a SYNC SAVE and exit */
         rdbSaveInfo rsi, *rsiptr;
         rsiptr = rdbPopulateSaveInfo(&rsi);
-        if (rdbSave(server.rdb_filename,rsiptr) != C_OK) {
+        if (rdbSave(SLAVE_REQ_NONE, server.rdb_filename,rsiptr) != C_OK) {
             /* Ooops.. error saving! The best we can do is to continue
              * operating. Note that if there was a background saving process,
              * in the next cron() Redis will be notified that the background