Running "lfs path2fid" on the Lustre mountpoint (e.g. /mnt/lustre) will return the underlying "ROOT/" directory inode number. This is bad for a number of reasons:

• it exposes the on-disk inode number to userspace as an IGIF value
• this will be broken after a backup/restore cycle
• this value is stored in the "link" xattr of all files in the ROOT/ directory

$ lfs path2fid /mnt/lustre
[0x61ab:0x6cad245e:0x0]

$ getfattr -d -m trusted.link -e hex /mnt/lustre/etc
getfattr: Removing leading '/' from absolute path names

1. file: mnt/lustre/etc
   trusted.link=0xdff1ea11010000002d000000000000000000000000000000001500000000000061ab6cad245e00000000657463

This should probably be fixed by moving MDD_ROOT_INDEX_OID to be 1UL or 2UL, and then returning FID_SEQ_START:MDD_ROOT_INDEX_OID to the client, like:

$ lfs path2fid /mnt/lustre
[0x200000000:0x2:0x0]

All that is needed is to ensure that the ROOT/ inode stores this in the LMA. This has the drawback that FID_SEQ_START is not currently exposed to clients and it fixes MDD_ROOT_INDEX_OID to a specific value (since it will be stored in the "link" xattr).

The alternative is to expose some other SEQ:OID for the root FID.