When using the llmount.sh script with TMP=/dev/shm it failed with:

1. Formatting mgs, mds, osts
2. Format mds1: /dev/shm/lustre-mdt1
3. mkfs.lustre: /dev/shm/lustre-mdt1 apparently does not exist
   #
4. mkfs.lustre FATAL: unable to prepare backend (2)
5. mkfs.lustre: exiting with 2 (No such file or directory)

This is certainly related to LU-1047 ("utils: mkfs shouldn't create loopback files in /dev")
This makes sense but it would be nice to declare /dev/shm as an exception.