Hi Linus, My finger slipped and I accidentally added you to the To: list on this new series. This series needs to go through review on linux-xfs; when this is ready to go I (or Dave) will send you a pull request. Sorry about the noise. --D On Tue, Apr 04, 2023 at 10:07:00AM -0700, Darrick J. Wong wrote: > Hi all, > > Last week, I was fiddling around with the metadump name obfuscation code > while writing a debugger command to generate directories full of names > that all have the same hash name. I had a few questions about how well > all that worked with ascii-ci mode, and discovered a nasty discrepancy > between the kernel and glibc's implementations of the tolower() > function. > > I discovered that I could create a directory that is large enough to > require separate leaf index blocks. The hashes stored in the dabtree > use the ascii-ci specific hash function, which uses a library function > to convert the name to lowercase before hashing. If the kernel and C > library's versions of tolower do not behave exactly identically, > xfs_ascii_ci_hashname will not produce the same results for the same > inputs. xfs_repair will deem the leaf information corrupt and rebuild > the directory. After that, lookups in the kernel will fail because the > hash index doesn't work. > > The kernel's tolower function will convert extended ascii uppercase > letters (e.g. A-with-umlaut) to extended ascii lowercase letters (e.g. > a-with-umlaut), whereas glibc's will only do that if you force LANG to > ascii. Tiny embedded libc implementations just plain won't do it at > all, and the result is a mess. Stabilize the behavior of the hash > function by encoding the kernel's tolower function in libxfs, add it to > the selftest, and fix xfs_scrub not handling this correctly. > > If you're going to start using this mess, you probably ought to just > pull from my git trees, which are linked below. > > This is an extraordinary way to destroy everything. Enjoy! > Comments and questions are, as always, welcome. > > --D > > kernel git tree: > https://git.kernel.org/cgit/linux/kernel/git/djwong/xfs-linux.git/log/?h=fix-asciici-tolower-6.3 > --- > fs/xfs/libxfs/xfs_dir2.c | 4 - > fs/xfs/libxfs/xfs_dir2.h | 20 ++++ > fs/xfs/scrub/dir.c | 7 +- > fs/xfs/xfs_dahash_test.c | 211 ++++++++++++++++++++++++---------------------- > 4 files changed, 139 insertions(+), 103 deletions(-) >
