On Thu, 2021-04-29 at 16:46 -0700, Patrick Donnelly wrote:
Hi Jeff,
On Thu, Apr 22, 2021 at 11:19 AM Jeff Layton <jlayton(a)redhat.com> wrote:
At this point, I'm thinking it might be best
to unify all of the
per-inode info into a single field that the MDS would treat as opaque.
Note that the alternate_names feature would remain more or less
untouched since it's associated more with dentries than inodes.
The initial version of this field would look something like this:
struct ceph_fscrypt_context {
u8 version; // == 1
struct fscrypt_context_v2 fscrypt_ctx; // 40 bytes
__le32 blocksize // 4k for now
__le64 size; // "real"
i_size
};
The MDS would send this along with any size updates (InodeStat, and
MClientCaps replies). The client would need to send this in cap
flushes/updates, and we'd also need to extend the SETATTR op too, so the
client can update this field in truncates (at least).
I don't look forward to having to plumb this into all of the different
client ops that can create inodes though. What I'm thinking we might
want to do is expose this field as the "ceph.fscrypt" vxattr.
I think the process for adding the fscrypt bits to the MClientRequest
will be the same as adding alternate_name? In the
ceph_mds_request_head payload. I don't like the idea of stuffing this
data in the xattr map.
That does sound considerably less hacky. I'll look into doing that.
The client can
stuff that into the xattr blob when creating a new inode,
and the MDS can scrape it out of that and move the data into the correct
field in the inode. A setxattr on this field would update the new field
too. It's an ugly interface, but shouldn't be too bad to handle and we
have some precedent for this sort of thing.
The rules for handling the new field in the client would be a bit weird
though. We'll need to allow it to reading the fscrypt_ctx part without
any caps (since that should be static once it's set), but the size
handling needs to be under the same caps as the traditional size field
(Is that Fsx? The rules for this are never quite clear to me.)
Would it be better to have two different fields here -- fscrypt_auth and
fscrypt_file? Or maybe, fscrypt_static/_dynamic? We don't necessarily
need to keep all of this info together, but it seemed neater that way.
I'm not seeing a reason to split the struct.
What caps should this live under? We have different requirements for
different parts of the struct.
1) fscrypt context: needs to be always available, especially when an
inode is initially instantiated, though it should almost always be
static once it's set. The exception is that an empty directory can grow
a new context when it's first encrypted, and we'll want other clients to
pick up on this change when it occurs.
2) "real" size: needs to be under Fwx, I think (though I need to look
more closely at the truncation path to be sure).
...and that's not even considering what rules we might want in the
future for other info we stuff into here. Given that the MDS needs to
treat this as opaque, what locks/caps should cover this new field?
--
Jeff Layton <jlayton(a)redhat.com>