On Tue, Feb 15, 2022 at 05:16:33PM -0800, Darrick J. Wong wrote: > On Tue, Feb 15, 2022 at 06:46:16PM +0530, Chandan Babu R wrote: > > On 15 Feb 2022 at 17:03, Chandan Babu R wrote: > > > On 15 Feb 2022 at 15:03, Dave Chinner wrote: > > >> On Tue, Feb 15, 2022 at 12:18:50PM +0530, Chandan Babu R wrote: > > >>> On 14 Feb 2022 at 22:37, Darrick J. Wong wrote: > > >>> > On Fri, Feb 11, 2022 at 05:40:30PM +0530, Chandan Babu R wrote: > > >>> >> On 07 Feb 2022 at 22:41, Darrick J. Wong wrote: > > >>> >> > On Mon, Feb 07, 2022 at 10:25:19AM +0530, Chandan Babu R wrote: > > >>> >> >> On 02 Feb 2022 at 01:31, Darrick J. Wong wrote: > > >>> >> >> > On Fri, Jan 21, 2022 at 10:48:54AM +0530, Chandan Babu R wrote: > > >>> >> >> I went through all the call sites of xfs_iext_count_may_overflow() and I think > > >>> >> >> that your suggestion can be implemented. > > >>> >> > > >>> >> Sorry, I missed/overlooked the usage of xfs_iext_count_may_overflow() in > > >>> >> xfs_symlink(). > > >>> >> > > >>> >> Just after invoking xfs_iext_count_may_overflow(), we execute the following > > >>> >> steps, > > >>> >> > > >>> >> 1. Allocate inode chunk > > >>> >> 2. Initialize inode chunk. > > >>> >> 3. Insert record into inobt/finobt. > > >>> >> 4. Roll the transaction. > > >>> >> 5. Allocate ondisk inode. > > >>> >> 6. Add directory inode to transaction. > > >>> >> 7. Allocate blocks to store symbolic link path name. > > >>> >> 8. Log symlink's inode (data fork contains block mappings). > > >>> >> 9. Log data blocks containing symbolic link path name. > > >>> >> 10. Add name to directory and log directory's blocks. > > >>> >> 11. Log directory inode. > > >>> >> 12. Commit transaction. > > >>> >> > > >>> >> xfs_trans_roll() invoked in step 4 would mean that we cannot move step 6 to > > >>> >> occur before step 1 since xfs_trans_roll would unlock the inode by executing > > >>> >> xfs_inode_item_committing(). > > >>> >> > > >>> >> xfs_create() has a similar flow. > > >>> >> > > >>> >> Hence, I think we should retain the current logic of setting > > >>> >> XFS_DIFLAG2_NREXT64 just after reading the inode from the disk. > > >>> > > > >>> > File creation shouldn't ever run into problems with > > >>> > xfs_iext_count_may_overflow because (a) only symlinks get created with > > >>> > mapped blocks, and never more than two; and (b) we always set NREXT64 > > >>> > (the inode flag) on new files if NREXT64 (the superblock feature bit) is > > >>> > enabled, so a newly created file will never require upgrading. > > >>> > > >>> The inode representing the symbolic link being created cannot overflow its > > >>> data fork extent count field. However, the inode representing the directory > > >>> inside which the symbolic link entry is being created, might overflow its data > > >>> fork extent count field. > > >> > > >> I dont' think that can happen. A directory is limited in size to 3 > > >> segments of 32GB each. In reality, only the data segment can ever > > >> reach 32GB as both the dabtree and free space segments are just > > >> compact indexes of the contents of the 32GB data segment. > > >> > > >> Hence a directory is never likely to reach more than about 40GB of > > >> blocks which is nowhere near large enough to overflowing a 32 bit > > >> extent count field. > > > > > > I think you are right. > > > > > > The maximum file size that can be represented by the data fork extent counter > > > in the worst case occurs when all extents are 1 block in size and each block > > > is 1k in size. > > > > > > With 1k byte sized blocks, a file can reach upto, > > > 1k * (2^31) = 2048 GB > > > > > > This is much larger than the asymptotic maximum size of a directory i.e. > > > 32GB * 3 = 96GB. > > The downside of getting rid of the checks for directories is that we > won't be able to use the error injection knob that limits all forks to > 10 extents max to see what happens when that part of directory expansion > fails. But if it makes it easier to handle nrext64, then that's > probably a good enough reason to forego that. If you want error injection to do that, add explicit error injection to the directory code. > > xfs_bmap_del_extent_real() > > Not sure about this one, since it actually /can/ result in more extents. Yup, unlikely to ever trigger, but still necessary for correctness. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx
