Add bcachefs storage driver with subvolume/snapshot support

[ticpu]

Implement a new storage driver for bcachefs filesystems that uses subvolumes and snapshots for container layer management, similar to the existing btrfs driver.

Features:

• Implementation using direct ioctl syscalls
• Subvolume creation via BCH_IOCTL_SUBVOLUME_CREATE
• Snapshot creation with BCH_SUBVOL_SNAPSHOT_CREATE flag
• Subvolume detection using statx() with STATX_SUBVOL
• Recursive nested subvolume deletion
• Support for both root and rootless operation

Tested on my system with multiple images:

❯ podman run --rm docker.io/library/nginx:latest nginx -v
Trying to pull docker.io/library/nginx:latest...
Getting image source signatures
Copying blob 53d743880af4 done   | 
Copying blob 0e4bc2bd6656 done   | 
Copying blob 108ab8292820 done   | 
Copying blob 192e2451f875 done   | 
Copying blob 77fa2eb06317 done   | 
Copying blob b5feb73171bf done   | 
Copying blob de57a609c9d5 done   | 
Copying config 60adc2e137 done   | 
Writing manifest to image destination
/docker-entrypoint.sh: /docker-entrypoint.d/ is not empty, will attempt to perform configuration
/docker-entrypoint.sh: Looking for shell scripts in /docker-entrypoint.d/
/docker-entrypoint.sh: Launching /docker-entrypoint.d/10-listen-on-ipv6-by-default.sh
10-listen-on-ipv6-by-default.sh: info: Getting the checksum of /etc/nginx/conf.d/default.conf
10-listen-on-ipv6-by-default.sh: info: Enabled listen on IPv6 in /etc/nginx/conf.d/default.conf
/docker-entrypoint.sh: Sourcing /docker-entrypoint.d/15-local-resolvers.envsh
/docker-entrypoint.sh: Launching /docker-entrypoint.d/20-envsubst-on-templates.sh
/docker-entrypoint.sh: Launching /docker-entrypoint.d/30-tune-worker-processes.sh
/docker-entrypoint.sh: Configuration complete; ready for start up
nginx version: nginx/1.29.3

❯ podman run --rm docker.io/library/python:3.12-slim python --version
Trying to pull docker.io/library/python:3.12-slim...
Getting image source signatures
Copying blob b7ba6d2a1fc7 done   | 
Copying blob 490b9a1c25e4 done   | 
Copying blob 0e4bc2bd6656 skipped: already exists  
Copying blob 0674d14a155c done   | 
Copying config 445121148b done   | 
Writing manifest to image destination
Python 3.12.12

❯ podman image mount ceph:v18 
/var/lib/containers/storage/bcachefs/subvolumes/7a295044d828c8a95725ef60009582c7a8a0c455ab9abd9ee9b350b0dd4c6d30

❯ ls /var/lib/containers/storage/bcachefs/subvolumes/7a295044d828c8a95725ef60009582c7a8a0c455ab9abd9ee9b350b0dd4c6d30
afs  bin  boot  dev  etc  home  lib  lib64  lost+found  media  mnt  opt  proc  root  run  sbin  srv  sys  tmp  usr  var

❯ podman run --rm --entrypoint=/bin/python3 -ti ceph:v18 
Python 3.9.21 (main, Feb 10 2025, 00:00:00) 
[GCC 11.5.0 20240719 (Red Hat 11.5.0-5)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>>

❯ podman image ls
REPOSITORY                TAG         IMAGE ID      CREATED       SIZE
docker.io/library/python  3.12-slim   445121148b18  13 days ago   123 MB
docker.io/library/nginx   latest      60adc2e137e7  13 days ago   155 MB
docker.io/library/alpine  latest      706db57fb206  7 weeks ago   8.62 MB
quay.io/ceph/ceph         v18         0f5473a1e726  6 months ago  1.27 GB

❯ podman image rm ceph:v18 
Error: image used by 085e9c2853013e627c41e8e1833655a7b73cf4ba45a19556102c3675dc840900: image is in use by a container: consider listing external containers and force-removing image

❯ podman rm -f ceph18 
ceph18

❯ podman image rm ceph:v18 
Untagged: quay.io/ceph/ceph:v18
Deleted: 0f5473a1e726b0feaff0f41f8de8341c0a94f60365d4584f4c10bd6b40d44bc1

❯ pwd && ls | wc -l
/var/lib/containers/storage/bcachefs/subvolumes
11

❯ podman image prune -a
WARNING! This command removes all images without at least one container associated with them.
Are you sure you want to continue? [y/N] y
706db57fb2063f39f69632c5b5c9c439633fda35110e65587c5d85553fd1cc38
60adc2e137e757418d4d771822fa3b3f5d3b4ad58ef2385d200c9ee78375b6d5
445121148b187db67e48799f002500623fa22d9f635e522f4e0f345414bd9107

❯ ls | wc -l
0

[github-actions]

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This pull-request has been approved by: ticpu
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