Documentation/filesystems/idmappings.rst

382     - mount's idmapping (``mnt_idmap(vfsmnt)``)
384 Let's see some examples with caller/filesystem idmapping but without mount
386 revisit/reconsider these examples, this time using mount idmappings, to see how
469 userspace id. We could only do this if we were to mount the whole filesystem
606 change in ownership is tied to the lifetime of the filesystem mount, i.e. the
608 filesystem and mount it again in another user namespace. This is usually
625 localized way. The ownership changes are restricted to a specific mount and the
626 ownership changes are tied to the lifetime of the mount. All other users and
631 completely under an idmapped mount to get the same effect. This has the
638 Filesystem types vs idmapped mount types
642 filesystem ownership and mount ownership of a VFS object such as an inode. The
644 perspective than when looked at from an idmapped mount. Such fundamental
646 So, to distinguish idmapped mount ownership from filesystem ownership separate
651 has been generated using a mount idmapping then we will be using the dedicated
671 change ownership of an inode from an idmapped mount. After we generated
672 a ``vfsuid_t`` or ``vfsgid_t`` based on the mount idmapping we later commit to
681 and ``vfsgid_t`` is specific to an idmapped mount.
684 on mount idmappings whereas ``kuid_t`` and ``kgid_t`` types are generated based
686 ``vfsuid_t`` or ``vfsgid_t`` types or mount idmappings to generate ``kuid_t``
687 or ``kgid_t`` types filesystem idmappings and mount idmappings are different
691 a mount idmapping to be passed which is of type ``struct mnt_idmap``. Passing
695 kernel ids with ``k`` we will prefix all VFS ids with ``v``. So a mount
707   VFS ids in the mount's idmapping::
712    /* Map the filesystem's userspace id down ito a VFS id in the mount's idmapping. */
713    make_kuid(mount, uid) = kuid
719   remapping the caller's VFS ids using the mount's idmapping::
721    /* Map the caller's VFS id up into a userspace id in the mount's idmapping. */
722    from_kuid(mount, kid) = uid
724    /* Map the mount's userspace id down into a kernel id in the filesystem's idmapping. */
736  mount idmapping:      u0:v10000:r10000
746 But when the caller is accessing the file on an idmapped mount the kernel will
748 id into a VFS id in the mount's idmapping::
754    /* Map the filesystem's userspace id down into a VFS id in the mount's idmapping. */
758 VFS id in the mount's idmapping into a userspace id in the caller's
773 But when the caller is accessing the file on an idmapped mount the kernel will
775 a VFS id according to the mount's idmapping::
778     /* Map the caller's kernel id up into a userspace id in the mount's idmapping. */
781     /* Map the mount's userspace id down into a kernel id in the filesystem's idmapping. */
791 preserving algorithm. A file created from ``u1000`` on an idmapped mount will
805  mount idmapping:      u0:v10000:r10000
808 the same idmapping to the mount. We now perform three steps:
818       /* Map the VFS id up into a userspace id in the mount's idmapping. */
839  mount idmapping:      u0:v10000:r10000
851        /* Map the VFS id up into a userspace id in the mount's idmapping. */
872  mount idmapping:      u0:v10000:r10000
882 2. Translate the kernel id into a VFS id in the mount's idmapping::
897 idmapping. With the idmapped mount in place it now can be crossmapped into the
898 filesystem's idmapping via the mount's idmapping. The file will now be created
899 with ``u1000`` according to the mount's idmapping.
909  mount idmapping:      u0:v10000:r10000
919 2. Translate the kernel id into a VFS id in the mount's idmapping::
934 idmapping. With the idmapped mount in place it now can be crossmapped into the
935 filesystem's idmapping via the mount's idmapping. The file is now owned by
936 ``u1000`` according to the mount's idmapping.
951 caller's or filesystem's idmapping according to the mount's idmapping.
956 and files on a per-mount basis.
968 mount for their home directory on their work computer or their computer at home
974 creates an idmapped mount with the minimal idmapping ``u1000:k1125:r1``. So now
981  mount idmapping:      u1000:v1125:r1
991       /* Map the VFS id up into a userspace id in the mount's idmapping. */
1012  mount idmapping:      u1000:v1125:r1
1019 2. Translate the kernel id into a VFS id in the mount's idmapping::
1038 ``u1000`` using the initial idmapping and mount the filesystem with the initial