Convert to const struct mnt_idmap. A mount's idmapping is immutable. The only thing that is allowed to be modified afterwards is the reference count and that is hidden behind mnt_idmap_get() and mnt_idmap_put(). Everything else only ever reads from the idmapping. This is the same model that struct cred uses and the idmapping is also rather sensitive. So make the idmap argument const wherever we can. The conversion is done from the bottom up so callers can continue to pass a non-const pointer to a const parameter until the conversion is finished. No functional changes. Link: https://patch.msgid.link/20260901-work-idmap-const-v1-22-54ccd48e100b@kernel.org Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Seth Forshee <sforshee@kernel.org> Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>