Hello,

I am looking at how to implement synthetic uid/gids for flex layout.

From rfc section "Implementation Notes for Synthetic uids/gids": [0]

" When the metadata server had a request to access a file, a SETATTR would be sent to the storage device to set the owner and group of the data file.  The user and group might be selected in a round robin fashion from the range of available ids. Those ids would be sent back as ffds_user and ffds_group to the client.  And it would present them as the RPC credentials to the storage device.  When the client was done accessing the file and the metadata server knew that no other client was accessing the file, it
could reset the owner and group to restrict access to the data file."

Few questions regarding implementation:

1. To implement it in nfs-ganesha, we would have to add a way to generate uids/gids, store a mapping between uids/gids and the corresponding data file. Is there already such structure in nfs-ganesha that can be reused?

2. As I understood, once metadata server generates uid/gid, it needs to send a setattr to the storage device to set owner and group of data file. But I am not sure how does this synthetic uid/gid maps to real uid/gid that a data file might have. The same data file in cephfs can be opened through clients other than nfs as well. 

[0] https://tools.ietf.org/html/draft-ietf-nfsv4-flex-files-19#page-3