Hi guys, I am trying to get a lower bound for unused inode number MSB on a mounted xfs super block, so I can publish it on struct super_block. This doesn't need to be a tight lower bound, but it needs to be a loewr bound that cannot change with growfs nor when remounting with different options (i.e. inode64). This is needed for overlayfs to be able to use the unused upper bits for overlayfs inode number namespace (see [1]). I realize that for a given agcount, a "soft" lower bound of unused upper bits is agno_log-agblklog-inopblog, which makes the "hard" lower bound 32-agblklog-inopblog, so I think I can use this number. I was staring at this definition and tried to figure out where this absolute limit of 56 used bits came from: #define XFS_MAXINUMBER ((xfs_ino_t)((1ULL << 56) - 1ULL)) Is this number really correct? If yes, then where does the constrain on maximum 56 bits come from? Thanks, Amir. [1] https://marc.info/?l=linux-unionfs&m=151007386419753&w=2 -- To unsubscribe from this list: send the line "unsubscribe linux-unionfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
