bindfs: Let mount find bindfs mount helper

[Balletie]

When mount is used with mount-type "fuse.bindfs", it cannot find the mount helper.

If mount can't find mount.fuse.bindfs, it executes the mount.fuse mount helper and passes fuse.bindfs as argument. Then mount.fuse tries to execute bindfs on its own, but it is not found in the PATH.

By creating a mount.fuse.bindfs link to the bindfs executable, this problem is avoided because mount will just execute the mount.fuse.bindfs mount helper without mount.fuse in the middle.

Things done:

• Tested using sandboxing (nix-build --option build-use-chroot true or nix.useChroot on NixOS)
• Built on platform(s)
  • NixOS
  • OS X
  • Linux
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Fits CONTRIBUTING.md.

More

cc @lovek323, Sorry for the duplicate PR.

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Please note, that points are not mandatory, but rather desired.

[mention-bot]

By analyzing the blame information on this pull request, we identified @lovek323 to be a potential reviewer

[lucabrunox]

Built locally, thanks.

[Balletie]

Hey cool, glad I could help :). By the way, for those on older versions of NixOS and who need to use specify mount-points with bindfs in their NixOS configuration, you can use this as a workaround:

fileSystems."/path/to/mount-point" =
  { device = "/path/to/device";
    # FIXME: Hack to workaround "command not found" bug
    fsType = "fuse./run/current-system/sw/bin/bindfs";
    options = "ro,map=501/1000:@20/@10";
  };