• Christian Brauner's avatar
    fs: support mapped mounts of mapped filesystems · bd303368
    Christian Brauner authored
    In previous patches we added new and modified existing helpers to handle
    idmapped mounts of filesystems mounted with an idmapping. In this final
    patch we convert all relevant places in the vfs to actually pass the
    filesystem's idmapping into these helpers.
    
    With this the vfs is in shape to handle idmapped mounts of filesystems
    mounted with an idmapping. Note that this is just the generic
    infrastructure. Actually adding support for idmapped mounts to a
    filesystem mountable with an idmapping is follow-up work.
    
    In this patch we extend the definition of an idmapped mount from a mount
    that that has the initial idmapping attached to it to a mount that has
    an idmapping attached to it which is not the same as the idmapping the
    filesystem was mounted with.
    
    As before we do not allow the initial idmapping to be attached to a
    mount. In addition this patch prevents that the idmapping the filesystem
    was mounted with can be attached to a mount created based on this
    filesystem.
    
    This has multiple reasons and advantages. First, attaching the initial
    idmapping or the filesystem's idmapping doesn't make much sense as in
    both cases the values of the i_{g,u}id and other places where k{g,u}ids
    are used do not change. Second, a user that really wants to do this for
    whatever reason can just create a separate dedicated identical idmapping
    to attach to the mount. Third, we can continue to use the initial
    idmapping as an indicator that a mount is not idmapped allowing us to
    continue to keep passing the initial idmapping into the mapping helpers
    to tell them that something isn't an idmapped mount even if the
    filesystem is mounted with an idmapping.
    
    Link: https://lore.kernel.org/r/20211123114227.3124056-11-brauner@kernel.org (v1)
    Link: https://lore.kernel.org/r/20211130121032.3753852-11-brauner@kernel.org (v2)
    Link: https://lore.kernel.org/r/20211203111707.3901969-11-brauner@kernel.org
    Cc: Seth Forshee <sforshee@digitalocean.com>
    Cc: Amir Goldstein <amir73il@gmail.com>
    Cc: Christoph Hellwig <hch@lst.de>
    Cc: Al Viro <viro@zeniv.linux.org.uk>
    CC: linux-fsdevel@vger.kernel.org
    Reviewed-by: default avatarSeth Forshee <sforshee@digitalocean.com>
    Signed-off-by: default avatarChristian Brauner <christian.brauner@ubuntu.com>
    bd303368
commoncap.c 43 KB