case-folding-fs

A case-insensitive FUSE filesystem.

case-folding-fs mounts over an existing directory and provides case-insensitive lookup within it (using Unicode case-folding). This is mainly useful for running scripts written on Mac OS or Windows that assume the filesystem is case-insensitive.

Build instructions

In the checkout directory:

cmake -S . -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build --target case-folding-fs

Usage instructions

Run build/case-folding-fs path/goes/here to mount over a particular directory. To unmount it, run fusermount3 -u path/goes/here. To mount it for running a single command, use the provided build/case-folding-wrap.sh script. For example, if you want to run /foo/command.py in the directory /bar/data, and you built the program in ~/case-folding-fs/build, do

cd /bar/data
~/case-folding-fs/build/case-folding-wrap.sh python /foo/command.py arg1 arg2 arg3

This will mount case-folding-fs over /bar/data, run python /foo/command.py arg1 arg2 arg3, and then unmount it.

Why should I use this instead of ciopfs?

• It mounts over the existing directory instead of having to use a separate mountpoint.
• It allows you to use an existing directory tree, instead of requiring the directory be prepared while mounted.
• When unmounted, all files retain their original name. ciopfs names the underlying files in lowercase and keeps the original name in an extended file attribute.

Why shouldn't I use this?

• It's slow.
  • It can open, read, and close a 1MiB file about 3000 times a second, in contrast to the native performance of 5000 times per second.
  • It can open, read, and close a 2 byte file about 50000 times a second, in contrast to the native performance of 750000 times per second (a 15x difference!).
• If you have 2 files with the same folded name, only one will be accessible (and which one it is is determined by the order that the underlying filesystem reports the files).
• Since it caches the entire directory tree, it will use a lot of memory if the tree is large and deeply nested.
• Since it caches the entire directory tree, if you modify the underlying filesystem while it is mounted it won't notice those changes.