On Fri, Jan 23, 2015 at 02:58:09PM +0300, Konstantin Khlebnikov wrote: > On 23.01.2015 04:53, Dave Chinner wrote: > >On Thu, Jan 22, 2015 at 06:28:51PM +0300, Konstantin Khlebnikov wrote: > >>>+ kprojid = make_kprojid(&init_user_ns, (projid_t)projid); > >> > >>Maybe current_user_ns()? > >>This code should be user-namespace aware from the beginning. > > > >No, the code is correct. Project quotas have nothing to do with > >UIDs and so should never have been included in the uid/gid > >namespace mapping infrastructure in the first place. > > Right, but user-namespace provides id mapping for project-id too. > This infrastructure adds support for nested project quotas with > virtualized ids in sub-containers. I couldn't say that this is > must have feature but implementation is trivial because whole > infrastructure is already here. This is an extremely common misunderstanding of project IDs. Project IDs are completely separate to the UID/GID namespace. Project quotas were originally designed specifically for accounting/enforcing quotas in situations where uid/gid accounting/enforcing is not possible. This design intent goes back 25 years - it predates XFS... IOWs, mapping prids via user namespaces defeats the purpose for which prids were originally intended for. > >Point in case: directory subtree quotas can be used as a resource > >controller for limiting space usage within separate containers that > >share the same underlying (large) filesystem via mount namespaces. > > That's exactly my use-case: 'sub-volumes' for containers with > quota for space usage/inodes count. That doesn't require mapped project IDs. Hard container space limits can only be controlled by the init namespace, and because inodes can hold only one project ID the current ns cannot be allowed to change the project ID on the inode because that allows them to escape the resource limits set on the project ID associated with the sub-mount set up by the init namespace... i.e. /mnt prid = 0, default for entire fs. /mnt/container1/ prid = 1, inherit, 10GB space limit /mnt/container2/ prid = 2, inherit, 50GB space limit ..... /mnt/containerN/ prid = N, inherit, 20GB space limit And you clone the mount namespace for each container so the root is at the appropriate /mnt/containerX/. Now the containers have a fixed amount of space they can use in the parent filesystem they know nothing about, and it is enforced by directory subquotas controlled by the init namespace. This "fixed amount of space" is reflected in the container namespace when "df" is run as it will report the project quota space limits. Adding or removing space to a container is as simple as changing the project quota limits from the init namespace. i.e. an admin operation controlled by the host, not the container.... Allowing the container to modify the prid and/or the inherit bit of inodes in it's namespace then means the user can define their own space usage limits, even turn them off. It's not a resource container at that point because the user can define their own limits. Hence, only if the current_ns cannot change project quotas will we have a hard fence on space usage that the container *cannot exceed*. Yes, I know there are other use cases for project quotas *within* a container as controlled by the user (same as existing project quota usages), but we don't have the capability of storing multiple project IDs on each inode, nor accounting/enforcement across multiple project IDs on an inode. Nor, really, do we want to (on disk format changes required) and hence we can have one or the other but not both. Further, in a containerised system, providing the admin with a trivial and easy to manage mechanism to provide hard limits on shared filesystem space usage of each container is far more important than catering to the occasional user who might have a need for project quotas inside a container. These are the points I brought up when I initially reviewed the user namespace patches - the userns developer ignored my concerns and the code was merged without acknowledging them, let alone addressing them. As we (the XFS guys) have no way of knowing when such a distinction should be made, and with the user ns developers being completely unresponsive on the subject, we made the decision ourselves. Our only concern was to be consistent, safe and predictable and that means we choose to only allow project quotas to be used as an external container resource hardwall limit and hence *never* allow access to project quotas inside container namespaces. That's the long and the short of it. project IDs are independent of user IDs and they cannot be sanely used both inside and outside user namespaces at the same time. Hence they should never have been included in the user namespace mappings in the first place. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
