Hi everyone, This deluge contains all of the additions to the parent pointers patchset that I've been working on for the past month. The kernel and xfsprogs patchsets are based on Allison's v9r2 tag from last week; the fstests patches are merely a part of my development tree. To recap Allison's cover letter: "The goal of this patch set is to add a parent pointer attribute to each inode. The attribute name containing the parent inode, generation, and directory offset, while the attribute value contains the file name. This feature will enable future optimizations for online scrub, shrink, nfs handles, verity, or any other feature that could make use of quickly deriving an inodes path from the mount point." The kernel branches start with a number of buf fixes that I need to get fstests to pass. I also restructured the kernel implementation of GETPARENTS to cut the memory usage considerably. For userspace, I cleaned up the xfsprogs patches so that libxfs-diff shows no discrepancies with the kernel and cleaned up the parent pointer usage code that I prototyped in 2017 so that it's less buggy and moldy. I also rewired xfs_scrub to use GETPARENTS to report file paths of corrupt files instead of inode numbers, since that part had bitrotted badly. With that out of the way, I implemented a prototype of online repairs for directories and parent pointers. This is only a proof of concept, because I had already backported many many patches from part 1 of online repair, and didn't feel like porting the parts needed to commit new structures atomically and reap the old dir/xattr blocks. IOWs, the prototype scans the filesystem to build a parallel directory or xattr structure, and then reports on any discrepancies between the two versions. Obviously this won't fix a corrupt directory tree, but it enables us to test the repair code on a consistent filesystem to demonstrate that it works. Next, I implemented fully functional parent pointer checking and repair for xfs_repair. This was less hard than I guessed it would be because the current design of phase 6 includes a walk of all directories. From the dirent data, we can build a per-AG index of all the parent pointers for all the inodes in that AG, then walk all the inodes in that AG to compare the lists. As you might guess, this eats a fair amount of memory, even with a rudimentary dirent name deduplication table to cut down on memory usage. After that, I moved on to solving the major problem that I've been having with the directory repair code, and that is the problem of reconstructing dirents at the offsets specified by the parent pointers. The details of the problem and how I dealt with it are captured in the cover letter for those patches. Suffice to say, we now encode the dirent name in the parent pointer attrname (or a collision resistant hash if it doesn't fit), which makes it possible to commit new directories atomically. The last part of this patchset reorganizes the XFS_IOC_GETPARENTS ioctl to encode variable length parent pointer records in the caller's buffer. The denser encodings mean that we can extract the parent list with fewer kernel calls. --D
