Merge patch series "afs: Dynamic root improvements"

David Howells <dhowells@redhat.com> says:

Here are some patches to make a number of improvements to the AFS dynamic
root:

 (1) Create an /afs/.<cell> mountpoint to match the /afs/<cell> mountpoint
     when a cell is created.

 (2) Add some more checks on cell names proposed by the user to prevent
     dodgy symlink bodies from being created.  Also prevent rootcell from
     being altered once set to simplify the locking.

 (3) Change the handling of /afs/@cell from being a dentry name
     substitution at lookup time to making it a symlink to the current cell
     name and also provide a /afs/.@cell symlink to point to the dotted
     cell mountpoint.

* patches from https://lore.kernel.org/r/20250107183454.608451-1-dhowells@redhat.com:
  afs: Make /afs/@cell and /afs/.@cell symlinks
  afs: Add rootcell checks
  afs: Make /afs/.<cell> as well as /afs/<cell> mountpoints

Link: https://lore.kernel.org/r/20250107183454.608451-1-dhowells@redhat.com
Signed-off-by: Christian Brauner <brauner@kernel.org>