25 Apr
2024
25 Apr
'24
6:22 p.m.
On Thursday, April 25, 2024 11:24:02 AM EDT Gregory Farnum wrote:
This mechanism should work the same with multiprotocol added into the mix. The
multiprotocol items would work like a new "flavor" in addition to nfs alone and
smb alone. Well managed multiprotocol would still need idmapping so the
mechanism would remain useful to isolate different idmappings (or lack thereof)
from stepping on each other.
I do plan on adding a mode (likely unsupported for downstream) where you can
entirely turn off this enforcement and live with the nightmare of handling all
the idmapping chaos and acl/non-acl based protocol mix yourself.
I don't know if we have any other useful boundary to operate on. If we try to
do it purely on a directory basis then we need to ensure that no parent dirs
OR child dirs have been earmarked and the latter kind of kills it for me. It
wouldn't be efficient to walk all child dirs every time you create a new share.
The subvolume boundary seems the most natural. Plus, that's what my downstream
is asking for. ;-)
Again, upstream users can choose to operate in the shoot-yourself-in-the foot
mode if they opt in.
That's fine. I knew it was a reach when I asked. :-)
On Wed, Apr 24, 2024 at 7:32 AM John Mulligan
<phlogistonjohn(a)asynchrono.us> wrote:
>
>
> Hi all,
>
>
>
> One of the items we need to do in preparation for supporting sharing
> CephFS
with SMB is to make the management layer, in particular our smb
and nfs MGR
modules, assist the admins by avoiding the situation where
the same directories are configured for nfs and smb access. We're mostly
focused on sharing out subvolumes. I've taken to calling the need to make
a subvolume exclusive to one protocol or the other as "earmarking" the
subvolume. We have rough design sketched out but I want to ask a few
questions, largely aimed at the file system team, before we proceed any
further.
Have you thought about how to handle it when we have deeper protocol
integration and actually do want to enable sharing of directories
across protocols?
Even without that, I know there's a problem mapping Windows ACLs
accurately into the NFS or POSIX security space, but IIUC there are
plenty of users who don't grab onto those edges and will actively move
data between applications using different protocols, so the ability to
swap them back and forth may also be important.
> First off, we intended to apply metadata to a subvolume when it is used by
> nfs
or smb for sharing. I've identified two candidates for storing the
> metadata: 1. storing it in xattrs in the root of
the subvolume
> 2. using the `ceph fs subvolume metadata ...` commands
>
>
>
> I am fairly familiar with xattrs and think they would be pretty
> appropriate
for this. Accessing them is easy with standard (libcephfs)
> file system APIs. One advantage of using xattrs
is that they'd also be
> visible to the protocol servers (samba/ganesha) and if we wanted to we
> could (re)use the metadata there too, if needed.
>
>
>
> I'm less familiar with the subvolume metadata commands. The docs say
> they're
for "custom metadata", something I think this falls
under. What
I'm less
certain of is if this is a good user case for this particular
kind of custom metadata. One good thing about this is that is clearly
specific to subvolumes. It also has the advantage that you can't
accidentally modify/remove an xattr via the network fs protocol like you
possibly could with an xattr over nfs/ smb.
It looks to me like "subvolume metadata" shoves the custom metadata
into a file in the fs, and was built for Ceph-CSI. Using it will put
it in a well-defined place, but will preclude this tooling from being
available to anybody who wants to export via Samba without using
subvolumes. I know you're focused on a subvolume solution, but I think
we'd rather not limit it to that if we don't have to?
However, a separate thing that just came up is that we want this
solution to support encrypted volumes as well — right now, we only
have fscrypt support via the kernel client, but we're working on
extending it to our userspace implementations as well. That has
implications for the design solution since we can't count on being
able to read user-visible metadata within lower directories until
after a key has been supplied (it's impacting our options for handling
samba's case-insensitivity). Not sure if this will matter for the
orchestration — for subvolumes, and probably for anything else, you
can always read the top-level info directory since the encryption
starts beneath that point.
> One last thought, and this is not a requirement but something that might
> be
interesting down the road is if we could hide directories, at the
CephFS level,
from some clients unless they explicitly opt-in to having
subvolumes earmarked to type X visible. IIRC hiding directories is
something that's already done for .snapshot dirs, right? If this seems
too strange, do not worry, I am not going to insist on it... I just
thought it might be cool to have in the future, but only if it's easy. I
only mention it in case this idea tips the scales a bit to either option
(1) or (2).
This isn't really a thing we do. The .snap directory is special-cased
throughout the code base, and it's not a real directory to begin with,
so it's not like we can set a flag and have clients hide an arbitrary
dir from listing. Sorry. :/
-Greg
>
>
> Once we decide on a method of storing metadata for a subvolume, I am also
> curious if anyone has opinions if we should have a single key-value pair
> for
all protocol specific "earmarking" metadata or split things
across
multiple
items. At least for smb, I want to reuse the feature not only to
block sharing a dir that's already shared with nfs but for blocking
(re)sharing dirs with incompatible idmapping/acl metadata. I see two
options, one where we store everything in a single key (hypothetically,
something like "smb.ad,idmapV1" or "smb.ad,id=foo". The other option
is
to use multiple key-value pairs. The first option has an advantage of
being more "atomic" and keeping everything together but the disadvantage
of needing to be parsed.
Any other thoughts on the subject would be welcome!
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