| Message ID | 20211130121032.3753852-6-brauner@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Extend and tweak mapping support | expand |
On Tue, Nov 30, 2021 at 01:10:27PM +0100, Christian Brauner wrote: > From: Christian Brauner <christian.brauner@ubuntu.com> > > Now that we implement the full remapping algorithms described in our > documentation remove the section about shortcircuting them. > > Link: https://lore.kernel.org/r/20211123114227.3124056-6-brauner@kernel.org (v1) > 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 > Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com> Reviewed-by: Seth Forshee <sforshee@digitalocean.com> > --- > /* v2 */ > unchanged > --- > Documentation/filesystems/idmappings.rst | 72 ------------------------ > 1 file changed, 72 deletions(-) > > diff --git a/Documentation/filesystems/idmappings.rst b/Documentation/filesystems/idmappings.rst > index 1229a75ec75d..7a879ec3b6bf 100644 > --- a/Documentation/filesystems/idmappings.rst > +++ b/Documentation/filesystems/idmappings.rst > @@ -952,75 +952,3 @@ The raw userspace id that is put on disk is ``u1000`` so when the user takes > their home directory back to their home computer where they are assigned > ``u1000`` using the initial idmapping and mount the filesystem with the initial > idmapping they will see all those files owned by ``u1000``. > - > -Shortcircuting > --------------- > - > -Currently, the implementation of idmapped mounts enforces that the filesystem > -is mounted with the initial idmapping. The reason is simply that none of the > -filesystems that we targeted were mountable with a non-initial idmapping. But > -that might change soon enough. As we've seen above, thanks to the properties of > -idmappings the translation works for both filesystems mounted with the initial > -idmapping and filesystem with non-initial idmappings. > - > -Based on this current restriction to filesystem mounted with the initial > -idmapping two noticeable shortcuts have been taken: > - > -1. We always stash a reference to the initial user namespace in ``struct > - vfsmount``. Idmapped mounts are thus mounts that have a non-initial user > - namespace attached to them. > - > - In order to support idmapped mounts this needs to be changed. Instead of > - stashing the initial user namespace the user namespace the filesystem was > - mounted with must be stashed. An idmapped mount is then any mount that has > - a different user namespace attached then the filesystem was mounted with. > - This has no user-visible consequences. > - > -2. The translation algorithms in ``mapped_fs*id()`` and ``i_*id_into_mnt()`` > - are simplified. > - > - Let's consider ``mapped_fs*id()`` first. This function translates the > - caller's kernel id into a kernel id in the filesystem's idmapping via > - a mount's idmapping. The full algorithm is:: > - > - mapped_fsuid(kid): > - /* Map the kernel id up into a userspace id in the mount's idmapping. */ > - from_kuid(mount-idmapping, kid) = uid > - > - /* Map the userspace id down into a kernel id in the filesystem's idmapping. */ > - make_kuid(filesystem-idmapping, uid) = kuid > - > - We know that the filesystem is always mounted with the initial idmapping as > - we enforce this in ``mount_setattr()``. So this can be shortened to:: > - > - mapped_fsuid(kid): > - /* Map the kernel id up into a userspace id in the mount's idmapping. */ > - from_kuid(mount-idmapping, kid) = uid > - > - /* Map the userspace id down into a kernel id in the filesystem's idmapping. */ > - KUIDT_INIT(uid) = kuid > - > - Similarly, for ``i_*id_into_mnt()`` which translated the filesystem's kernel > - id into a mount's kernel id:: > - > - i_uid_into_mnt(kid): > - /* Map the kernel id up into a userspace id in the filesystem's idmapping. */ > - from_kuid(filesystem-idmapping, kid) = uid > - > - /* Map the userspace id down into a kernel id in the mounts's idmapping. */ > - make_kuid(mount-idmapping, uid) = kuid > - > - Again, we know that the filesystem is always mounted with the initial > - idmapping as we enforce this in ``mount_setattr()``. So this can be > - shortened to:: > - > - i_uid_into_mnt(kid): > - /* Map the kernel id up into a userspace id in the filesystem's idmapping. */ > - __kuid_val(kid) = uid > - > - /* Map the userspace id down into a kernel id in the mounts's idmapping. */ > - make_kuid(mount-idmapping, uid) = kuid > - > -Handling filesystems mounted with non-initial idmappings requires that the > -translation functions be converted to their full form. They can still be > -shortcircuited on non-idmapped mounts. This has no user-visible consequences. > -- > 2.30.2 >
diff --git a/Documentation/filesystems/idmappings.rst b/Documentation/filesystems/idmappings.rst index 1229a75ec75d..7a879ec3b6bf 100644 --- a/Documentation/filesystems/idmappings.rst +++ b/Documentation/filesystems/idmappings.rst @@ -952,75 +952,3 @@ The raw userspace id that is put on disk is ``u1000`` so when the user takes their home directory back to their home computer where they are assigned ``u1000`` using the initial idmapping and mount the filesystem with the initial idmapping they will see all those files owned by ``u1000``. - -Shortcircuting --------------- - -Currently, the implementation of idmapped mounts enforces that the filesystem -is mounted with the initial idmapping. The reason is simply that none of the -filesystems that we targeted were mountable with a non-initial idmapping. But -that might change soon enough. As we've seen above, thanks to the properties of -idmappings the translation works for both filesystems mounted with the initial -idmapping and filesystem with non-initial idmappings. - -Based on this current restriction to filesystem mounted with the initial -idmapping two noticeable shortcuts have been taken: - -1. We always stash a reference to the initial user namespace in ``struct - vfsmount``. Idmapped mounts are thus mounts that have a non-initial user - namespace attached to them. - - In order to support idmapped mounts this needs to be changed. Instead of - stashing the initial user namespace the user namespace the filesystem was - mounted with must be stashed. An idmapped mount is then any mount that has - a different user namespace attached then the filesystem was mounted with. - This has no user-visible consequences. - -2. The translation algorithms in ``mapped_fs*id()`` and ``i_*id_into_mnt()`` - are simplified. - - Let's consider ``mapped_fs*id()`` first. This function translates the - caller's kernel id into a kernel id in the filesystem's idmapping via - a mount's idmapping. The full algorithm is:: - - mapped_fsuid(kid): - /* Map the kernel id up into a userspace id in the mount's idmapping. */ - from_kuid(mount-idmapping, kid) = uid - - /* Map the userspace id down into a kernel id in the filesystem's idmapping. */ - make_kuid(filesystem-idmapping, uid) = kuid - - We know that the filesystem is always mounted with the initial idmapping as - we enforce this in ``mount_setattr()``. So this can be shortened to:: - - mapped_fsuid(kid): - /* Map the kernel id up into a userspace id in the mount's idmapping. */ - from_kuid(mount-idmapping, kid) = uid - - /* Map the userspace id down into a kernel id in the filesystem's idmapping. */ - KUIDT_INIT(uid) = kuid - - Similarly, for ``i_*id_into_mnt()`` which translated the filesystem's kernel - id into a mount's kernel id:: - - i_uid_into_mnt(kid): - /* Map the kernel id up into a userspace id in the filesystem's idmapping. */ - from_kuid(filesystem-idmapping, kid) = uid - - /* Map the userspace id down into a kernel id in the mounts's idmapping. */ - make_kuid(mount-idmapping, uid) = kuid - - Again, we know that the filesystem is always mounted with the initial - idmapping as we enforce this in ``mount_setattr()``. So this can be - shortened to:: - - i_uid_into_mnt(kid): - /* Map the kernel id up into a userspace id in the filesystem's idmapping. */ - __kuid_val(kid) = uid - - /* Map the userspace id down into a kernel id in the mounts's idmapping. */ - make_kuid(mount-idmapping, uid) = kuid - -Handling filesystems mounted with non-initial idmappings requires that the -translation functions be converted to their full form. They can still be -shortcircuited on non-idmapped mounts. This has no user-visible consequences.