Re: [PATCH] generic/453: Exclude filenames that are not supported by exfat

["Theodore Ts'o" <tytso@mit.edu>]

On Tue, Apr 27, 2021 at 11:11:16AM -0700, Darrick J. Wong wrote:
> 
> TBH I think these tests (g/453 and g/454) are probably only useful for
> filesystems that allow unrestricted byte streams for names.

I'm actually a little puzzled about why these tests should exist:

# Create a directory with multiple filenames that all appear the same
# (in unicode, anyway) but point to different inodes.  In theory all
# Linux filesystems should allow this (filenames are a sequence of
# arbitrary bytes) even if the user implications are horrifying.

Why do we care about testing this?  The assertion "In all theory all
Linux filesystems should allow this" is clearly not true --- if you
enable unicode support for ext4 or f2fs, this will no longer be true,
and this is considered by some a _feature_ not a bug --- precisely
_because_ the user implications are horrifying.

So why does these tests exist?  Darrick, I see you added them in 2017
to test whether or not xfs_scrub will warn about confuable names, if
_check_xfs_scrub_does_unicode is true.  So we already understand that
it's possible for a file system checker to complain that these file
names are bad.

It's not at all clear to me that asserting that all Linux file systems
_must_ treat file names as "bag of bits" and not apply any kind of
unicode normalization or strict unicode validation is a valid thing to
test for in 2021.

					- Ted