--storageEngine confusingly reported as ignored in sharded deployments

[p-mongo]

I used mlaunch to create a sharded cluster using mmapv1 storage engine, as follows:

butler% mlaunch init --sharded 2 --replicaset 2 --storageEngine mmapv1 --dir /mnt/zram/sandbox/mmap1
warning: ignoring unknown argument --storageEngine for mongod
warning: ignoring unknown argument --storageEngine for mongos

Note that mlaunch stated it would ignore --storageEngine for mongod.

Requesting a replica set with mmapv1 does not produce either warning:

butler% mlaunch init  --replicaset 2 --storageEngine mmapv1 --dir /mnt/zram/sandbox/mmap2

However, looking at the created processes it appears that --storageEngine was in fact passed to mongod:

butler% ps awwxu|grep sandbox|grep 99
sandbox   7469  0.8  0.7 10345660 57944 ?      Sl   14:01   0:00 mongod --replSet replset --dbpath /mnt/zram/sandbox/mmap3/replset/rs1/db --logpath /mnt/zram/sandbox/mmap3/replset/rs1/mongod.log --port 9999 --fork --storageEngine mmapv1 --wiredTigerCacheSizeGB 1
sandbox   7492  0.8  1.1 6009996 88712 ?       Sl   14:01   0:00 mongod --replSet replset --dbpath /mnt/zram/sandbox/mmap3/replset/rs2/db --logpath /mnt/zram/sandbox/mmap3/replset/rs2/mongod.log --port 10000 --fork --storageEngine mmapv1 --wiredTigerCacheSizeGB 1
sandbox   7828  0.9  0.6 6180072 52832 ?       Sl   14:01   0:00 mongod --replSet shard01 --dbpath /mnt/zram/sandbox/mmap4/shard01/rs1/db --logpath /mnt/zram/sandbox/mmap4/shard01/rs1/mongod.log --port 9904 --fork --storageEngine mmapv1 --shardsvr --wiredTigerCacheSizeGB 1
sandbox   7852  1.0  1.0 6066372 86080 ?       Sl   14:01   0:00 mongod --replSet shard01 --dbpath /mnt/zram/sandbox/mmap4/shard01/rs2/db --logpath /mnt/zram/sandbox/mmap4/shard01/rs2/mongod.log --port 9905 --fork --storageEngine mmapv1 --shardsvr --wiredTigerCacheSizeGB 1
sandbox   7874  1.0  1.0 6074568 86500 ?       Sl   14:01   0:00 mongod --replSet shard01 --dbpath /mnt/zram/sandbox/mmap4/shard01/rs3/db --logpath /mnt/zram/sandbox/mmap4/shard01/rs3/mongod.log --port 9906 --fork --storageEngine mmapv1 --shardsvr --wiredTigerCacheSizeGB 1
sandbox   7896  0.9  0.6 6180076 53160 ?       Sl   14:01   0:00 mongod --replSet shard02 --dbpath /mnt/zram/sandbox/mmap4/shard02/rs1/db --logpath /mnt/zram/sandbox/mmap4/shard02/rs1/mongod.log --port 9907 --fork --storageEngine mmapv1 --shardsvr --wiredTigerCacheSizeGB 1
sandbox   7918  1.0  0.6 6066372 52212 ?       Sl   14:01   0:00 mongod --replSet shard02 --dbpath /mnt/zram/sandbox/mmap4/shard02/rs2/db --logpath /mnt/zram/sandbox/mmap4/shard02/rs2/mongod.log --port 9908 --fork --storageEngine mmapv1 --shardsvr --wiredTigerCacheSizeGB 1
sandbox   7943  0.9  0.6 6074568 52792 ?       Sl   14:01   0:00 mongod --replSet shard02 --dbpath /mnt/zram/sandbox/mmap4/shard02/rs3/db --logpath /mnt/zram/sandbox/mmap4/shard02/rs3/mongod.log --port 9909 --fork --storageEngine mmapv1 --shardsvr --wiredTigerCacheSizeGB 1
sandbox   7965  3.0  0.8 1473804 70168 ?       Sl   14:01   0:01 mongod --replSet configRepl --dbpath /mnt/zram/sandbox/mmap4/configRepl/rs1/db --logpath /mnt/zram/sandbox/mmap4/configRepl/rs1/mongod.log --port 9910 --fork --configsvr --wiredTigerCacheSizeGB 1
sandbox   8188  0.2  0.2 258100 22696 ?        Sl   14:01   0:00 mongos --logpath /mnt/zram/sandbox/mmap4/mongos.log --port 9903 --configdb configRepl/localhost:9910 --fork

Actual/current behavior

mlaunch states --storageEngine is ignored for mongod and mongos.

Expected behavior

I think the only warning should be that --storageEngine is ignored for mongos.

Environment

Software	Version
mtools	1.5.3
MongoDB server	4.0.9
Operating system	Debian