How to mount a squashfs file in a container when running rootless Podman?

squashfuse can be used to mount a squashfs archive inside a container.

Example on a Fedora 34 computer

1. Build a squashfuse container image from this Dockerfile

   FROM docker.io/library/fedora
   RUN dnf install -y squashfuse fuse
   

   with podman build

   [testuser@laptop ~]$ mkdir squashfuse_container
   [testuser@laptop ~]$ emacs -nw squashfuse_container/Dockerfile
   [testuser@laptop ~]$ cat squashfuse_container/Dockerfile
   FROM docker.io/library/fedora
   RUN dnf install -y squashfuse fuse
   [testuser@laptop ~]$ podman --version
   podman version 3.4.1
   [testuser@laptop ~]$ podman build -q -t squashfuse squashfuse_container/
   1c2a97ccd71698978973ddc534b96f955a96aad89aef447456d3d327957faeb6
   [testuser@laptop ~]$
   

2. Create a squashfs file (data.squash) with mksquashfs

   [testuser@laptop ~]$ mkdir data
   [testuser@laptop ~]$ echo foo > data/file1.txt
   [testuser@laptop ~]$ echo bar > data/file2.txt
   [testuser@laptop ~]$ mkdir res
   [testuser@laptop ~]$ mksquashfs data res/data.squash
   Parallel mksquashfs: Using 8 processors
   Creating 4.0 filesystem on res/data.squash, block size 131072.
   [================================================================|] 2/2 100%
   
   Exportable Squashfs 4.0 filesystem, gzip compressed, data block size 131072
       compressed data, compressed metadata, compressed fragments,
       compressed xattrs, compressed ids
       duplicates are removed
   Filesystem size 0.35 Kbytes (0.00 Mbytes)
       76.28% of uncompressed filesystem size (0.46 Kbytes)
   Inode table size 55 bytes (0.05 Kbytes)
       35.71% of uncompressed inode table size (154 bytes)
   Directory table size 36 bytes (0.04 Kbytes)
       75.00% of uncompressed directory table size (48 bytes)
   Xattr table size 54 bytes (0.05 Kbytes)
       100.00% of uncompressed xattr table size (54 bytes)
   Number of duplicate files found 0
   Number of inodes 3
   Number of files 2
   Number of fragments 1
   Number of symbolic links 0
   Number of device nodes 0
   Number of fifo nodes 0
   Number of socket nodes 0
   Number of directories 1
   Number of ids (unique uids + gids) 1
   Number of uids 1
       testuser (1007)
   Number of gids 1
       testuser (1007)
   [testuser@laptop ~]$ ls -l res/
   total 4
   -rw-r--r--. 1 testuser testuser 4096 Oct 31 11:06 data.squash
   [testuser@laptop ~]$ 
   

3. Run podman run and then use squashfuse to mount the squashfs archive

   [testuser@laptop ~]$ podman run --rm \
                                   --cap-add=sys_admin \
                                   --device /dev/fuse \
                                   -v ./res/data.squash:/a:Z \
                                   -ti localhost/squashfuse
   [root@1e6860530222 /]# mkdir /mnt/dir
   [root@1e6860530222 /]# squashfuse /a /mnt/dir
   [root@1e6860530222 /]# ls -l /mnt/dir
   total 0
   -rw-r--r--. 1 1007 1007 4 Oct 31 09:31 file1.txt
   -rw-r--r--. 1 1007 1007 4 Oct 31 09:31 file2.txt
   [root@1e6860530222 /]# cat /mnt/dir/file1.txt 
   foo
   [root@1e6860530222 /]# cat /mnt/dir/file2.txt 
   bar
   [root@1e6860530222 /]# exit
   exit
   [testuser@laptop ~]$ 
   

   The same commands on one line. (Removing -ti for this non-interactive version):

   podman run --rm --cap-add=sys_admin --device /dev/fuse -v ./res/data.squash:/a:Z localhost/squashfuse /bin/bash -c "mkdir /mnt/dir ; squashfuse /a /mnt/dir; ls -l /mnt/dir; cat /mnt/dir/file1.txt; cat /mnt/dir/file2.txt"