On Fri, Mar 16, 2018 at 4:05 PM, Amir Goldstein <amir73il@xxxxxxxxx> wrote: > 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" Hmm, I copied that typo from the comment in xfs_format.h. Unless I am missing something the amount of unused upper bits is 64 - agno_log - agblklog - inopblog. Hence the "hard" limit below: > 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
