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. -- chandan
