5.6 KiB
Tar FUSE
This program mounts a tar file system to a directory through FUSE.
Have you ever wanted to have a nice, convenient view into a tar file without
having to unpack it, and without having to learn a ton of obscure tar commands?
Have you ever wanted to be able to do find -type f -name "*.ml", or any other
search command, only inside a tar file?
If you've experienced any of the above, this is your lucky day! Just mount the tar file to a directory with fusetar! This program allows you to mount a tar file as if it were a disk or some other filesystem-containing device. The files inside the archive are presented transparently as if they were files in a regular filesystem.
Some advantages of doing this instead of just extracting the tarball:
This does not require extraction - you can just mount, take a peek, search through files and copy files out, then unmount. This program only performs read operations, the archive is not modified.
This also means that your filesystem is not polluted. For example, if you wanted to search for a particular file's contents, you would normally have to extract the archive and search with find. If the archive is large, this is potentially expensive. With this program you don't have to do any of that - just mount it!
It doesn't keep the entire file in memory, so you can still access arbitrarily large tar files. File contents will only be fetched from disk when requested.
Finally, your access to the archive is fully transparent. You do not need to learn any flags or anything - any commands that search through, index or otherwise access files will now work on tar.
Some disadvantages:
It's always read-only, so the contents of your archive are preserved. Tar is a streaming format, and it is quite awkward to try to make changes/additions to it, which is why the program currently does not support write operations.
I/O performance may be affected. As mentioned, tar is a streaming format, and therefore file access can be inefficient.
Examples
$ fusetar my-archive.tar mnt/
And just like that, everything inside the tarball is available to you as a read-only file system, to search, read or do whatever else.
Debian rootfs
An example with the debian rootfs:
$ wget https://github.com/kbaraniak/debian-rootfs/releases/download/bookworm-270224/debian-amd64-bookworm-rootfs-270224.tar.xz
...
$ xz -d debian-amd64-bookworm-rootfs-270224.tar.xz
$ mkdir -p mnt
$ fusetar debian-amd64-bookworm-rootfs-270224.tar mnt/
$ ls mnt/
bin boot dev etc home lib lib64 media mnt opt proc root run sbin srv sys tmp usr var
As you can see, the root file system inside the tar archive is transparently presented to you now under your mounted directory!
With that being said, if you absolutely need to write files to the directory (but not to the archive), it is quite easy to make this directory writable - you can simply use overlayfs to overlay an empty directory over this mount. This way, your changes would be preserved inside a separate directory, while unchanged content from the archive remains available:
$ mkdir -p mnt/ upper/ workdir/ merged/
$ ./main.exe debian-amd64-bookworm-rootfs-270224.tar -f mnt &
[1] 46526
$ sudo mount -t overlay overlay -olowerdir=./mnt,upperdir=./upper,workdir=./workdir ./merged
$ echo "hi" > merged/hello-world.txt
$ ls -la merged
total 5
drwxr-xr-x 1 haxala1r users 30 Nov 27 17:37 .
drwxr-xr-x 1 haxala1r users 362 Nov 27 17:36 ..
lrwxrwxrwx 1 root root 0 Jul 2 2023 bin -> usr/bin
drwxr-xr-x 1 root root 0 Jul 2 2023 boot
drwxr-xr-x 1 root root 0 Feb 27 2024 dev
drwxr-xr-x 1 root root 0 Feb 27 2024 etc
-rw-r--r-- 1 haxala1r users 3 Nov 27 17:37 hello-world.txt
drwxr-xr-x 1 root root 0 Jul 2 2023 home
lrwxrwxrwx 1 root root 0 Jul 2 2023 lib -> usr/lib
lrwxrwxrwx 1 root root 0 Jul 2 2023 lib64 -> usr/lib64
drwxr-xr-x 1 root root 0 Jul 2 2023 media
drwxr-xr-x 1 root root 0 Jul 2 2023 mnt
drwxr-xr-x 1 root root 0 Jul 2 2023 opt
drwxr-xr-x 1 root root 0 Jul 2 2023 proc
drwxr-xr-x 1 root root 0 Feb 27 2024 root
drwxr-xr-x 1 root root 0 Jul 2 2023 run
lrwxrwxrwx 1 root root 0 Jul 2 2023 sbin -> usr/sbin
drwxr-xr-x 1 root root 0 Jul 2 2023 srv
dr-xr-xr-x 1 root root 0 Feb 27 2024 sys
drwxr-xr-x 1 root root 0 Jul 2 2023 tmp
drwxr-xr-x 1 root root 0 Jul 2 2023 usr
drwxr-xr-x 1 root root 0 Feb 27 2024 var
Build
In order to build this program, you need to have the following installed:
- ocaml 5.3
- dune 3
- ocamlfuse
- findlib
You can install all of these through opam, or through your distribution's package manager if your distribution packages them.
Once you have these, you can build with dune build, and install with dune install. You can tell it where to install, e.g. dune install --prefix /usr/local/.
Nix
If you are on NixOS, or are willing to install the nix package manager, you can also use the provided default.nix (just run nix-build). This will download all dependancies and build. It should produce a symlink called result, which will point to the results (containing the produced binary under bin/). You can then place the binary wherever you like.
For development purposes, you can also use the provided shell.nix, with nix-shell. This will drop you in a development shell, with all necessary packages to build & develop.
If you have nix and direnv (with nix-direnv) installed, you can simply allow the provided .env file. This will automatically put you in a shell environment with all necessary packages.