On Thu, Dec 16, 2021 at 04:05:37PM +1100, Dave Chinner wrote: > On Wed, Dec 15, 2021 at 05:09:32PM -0800, Darrick J. Wong wrote: > > From: Darrick J. Wong <djwong@xxxxxxxxxx> > > > > When xfs_scrub encounters a directory with a leaf1 block, it tries to > > validate that the leaf1 block's bestcount (aka the best free count of > > each directory data block) is the correct size. Previously, this author > > believed that comparing bestcount to the directory isize (since > > directory data blocks are under isize, and leaf/bestfree blocks are > > above it) was sufficient. > > > > Unfortunately during testing of online repair, it was discovered that it > > is possible to create a directory with a hole between the last directory > > block and isize. > > We have xfs_da3_swap_lastblock() that can leave an -empty- da block > between the last referenced block and isize, but that's not a "hole" > in the file. If you don't mean xfs_da3_swap_lastblock(), then can > you clarify what you mean by a "hole" here and explain to me how the > situation it occurs in comes about? I don't actually know how it comes about. I wrote a test that sets up fsstress to expand and contract directories and races xfs_scrub -n, and noticed that I'd periodically get complaints about directories (usually $SCRATCH_MNT/p$CPU) where the last block(s) before i_size were actually holes. I began reading the dir2 code to try to figure out how this came about (clearly we're not updating i_size somewhere) but then took the shortcut of seeing if xfs_repair or xfs_check complained about this situation. Neither of them did, and I found a couple more directories in a similar situation on my crash test dummy machine, and concluded "Wellllp, I guess this is part of the ondisk format!" and committed the patch. Also, I thought xfs_da3_swap_lastblock only operates on leaf and da btree blocks, not the blocks containing directory entries? I /think/ the actual explanation is that something goes wrong in xfs_dir2_shrink_inode (maybe?) such that the mapping goes away but i_disk_size doesn't get updated? Not sure how /that/ can happen, though... --D > > Cheers, > > Dave. > -- > Dave Chinner > david@xxxxxxxxxxxxx
