On Wed, Feb 18, 2015 at 3:30 PM, Florian Haas <flor...@hastexo.com> wrote: > On Wed, Feb 18, 2015 at 11:41 PM, Gregory Farnum <g...@gregs42.com> wrote: >> On Wed, Feb 18, 2015 at 1:58 PM, Florian Haas <flor...@hastexo.com> wrote: >>> On Wed, Feb 18, 2015 at 10:28 PM, Oliver Schulz <osch...@mpp.mpg.de> wrote: >>>> Dear Ceph Experts, >>>> >>>> is it possible to define a Ceph user/key with privileges >>>> that allow for read-only CephFS access but do not allow >>>> write or other modifications to the Ceph cluster? >>> >>> Warning, read this to the end, don't blindly do as I say. :) >>> >>> All you should need to do is define a CephX identity that has only r >>> capabilities on the data pool (assuming you're using a default >>> configuration where your CephFS uses the data and metadata pools): >>> >>> sudo ceph auth get-or-create client.readonly mds 'allow' osd 'allow r >>> pool=data' mon 'allow r' >>> >>> That identity should then be able to mount the filesystem but not >>> write any data (use "ceph-fuse -n client.readonly" or "mount -t ceph >>> -o name=readonly") >>> >>> That said, just touching files or creating them is only a metadata >>> operation that doesn't change anything in the data pool, so I think >>> that might still be allowed under these circumstances. >> >> ...and deletes, unfortunately. :( > > If the file being deleted is empty, yes. If the file has any content, > then the removal should hit the data pool before it hits metadata, and > should fail there. No?
No, all data deletion is handled by the MDS, for two reasons: 1) You don't want clients to have to block on deletes in time linear with the number of objects 2) (IMPORTANT) if clients unlink a file which is still opened elsewhere, it can't be deleted until closed. ;) > >>I don't think this is presently a >> thing it's possible to do until we get a much better user auth >> capabilities system into CephFS. >> >>> >>> However, I've just tried the above with ceph-fuse on firefly, and I >>> was able to mount the filesystem that way and then echo something into >>> a previously existing file. After unmounting, remounting, and trying >>> to cat that file, I/O just hangs. It eventually does complete, but >>> this looks really fishy. >> >> This is happening because the CephFS clients don't (can't, really, for >> all the time we've spent thinking about it) check whether they have >> read permissions on the underlying pool when buffering writes for a >> file. I believe if you ran an fsync on the file you'd get an EROFS or >> similar. >> Anyway, the client happily buffers up the writes. Depending on how >> exactly you remount then it might not be able to drop the MDS caps for >> file access (due to having dirty data it can't get rid of), and those >> caps have to time out before anybody else can access the file again. >> So you've found an unpleasant oddity of how the POSIX interfaces map >> onto this kind of distributed system, but nothing unexpected. :) > > Oliver's point is valid though; I would be nice if you could somehow > make CephFS read-only to some (or all) clients server side, the way an > NFS ro export does. Yeah. Yet another thing that would be good but requires real permission bits on the MDS. It'll happen eventually, but we have other bits that seem a lot more important...fsck, stability, single-tenant usability.... _______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
