Adding Debian fuse support

[m0ntyG]

Hi, this PR adds Debian fuse mount support: https://torsion.org/borgmatic/docs/how-to/extract-a-backup/

Omit the --archive flag to mount all archives (lazy-loaded):

borgmatic mount --mount-point /mnt

Or use the "latest" value for the archive to mount the latest successful archive:

borgmatic mount --archive latest --mount-point /mnt

[m3nu]

Shall we make this optional, since many people don't need this feature and/or have strong opinions about not wanting FUSE installed. Just my experience. 😄

[m0ntyG]

Hi, proposal for an optional fuse support

[m3nu]

Kudos for taking care of ALL the OSs. 😄

Let's run those tests and then merge it.

[m3nu]

Hmm. Our tests don't try different parameters yet. So it won't test the FUSE option. Todo for me to add this later.

[HolyMacarony]

Dear Developers,

I've been trying for several days to configure borgmatic to mount Borg repositories on my Debian system, but I'm stuck. I would greatly appreciate any insights into what I might be misunderstanding about how this should work with borgmatic.

From my research, I understand that to enable FUSE support for Borg on Debian, it needs to be installed via pip in its own virtual environment. I've successfully done this manually:

https://borgbackup.readthedocs.io/en/stable/installation.html#using-pip
virtualenv --python=python3 borg-env
source borg-env/bin/activate

# might be required if your tools are outdated
pip install -U pip setuptools wheel

# install Borg + Python dependencies into virtualenv
pip install borgbackup
# or alternatively (if you want FUSE support):
pip install borgbackup[llfuse]  # to use llfuse
pip install borgbackup[pyfuse3]  # to use pyfuse3

This manual installation works perfectly (Step 1 complete).

However, borgmatic creates its own virtual environment in /opt/borgmatic with separate installations of both borgmatic and Borg. As mentioned by @m3nu in this comment, these installations intentionally lack FUSE support (while I don't understand the rationale for excluding mount capabilities, I assume there are valid reasons).

From the role's documentation, I see these relevant options:
borg_pip_packages: Dependancy Packages (pip) to install borg(backup) and borgmatic. borg_venv_path: Path to store the venv for borg(backup) and borgmatic
I attempted to:

• Add borg_pip_packages: "borgbackup[pyfuse3]" to my Ansible variables, but received:
  No package(s) matching 'borgbackup[pyfuse3]' available

• Redirect borg_venv_path to my manually created venv, but this approach also failed

After this experimentation, I've concluded that the intended workflow is:

If FUSE support is needed for either Borg or borgmatic, you must:

• Manually create a separate virtual environment

• Install with FUSE support (llfuse/pyfuse3)

• Use this venv specifically for mounting operations

This appears to be the only currently working solution.

Thank you for your time and assistance!