On 2019-08-01T19:03:11, Sage Weil <sage@newdream.net> wrote:
Is a virtual xattr on a virtual directory a bad idea? Seems fine to me. It is a bit awkward from the command line, though.
Well, [gs]etfattr exist, so not too bad, but I agree:
What about 'chattr +e' (or 'chattr -e'), which normally sets the immutable flag for local file systems?
Yes, I think that's better. (Though I think you mean "i", not "e"?) One of the reasons for why we considered xattrs though was that it'd allow us to store some more metadata associated with the snap. Consider - when creating a snap of "dir", is the ctime/mtime of the dir/.snap/name now the values of "dir/." at the time of the snapshot, or the snapshot creation time? I think the the former would make more sense, but where then to store the snap creation time? Let's stuff it into an xattr. Similarly, we talked to someone very familiar with NetApp, and they mentioned that it can be hard to figure out when/who/why a snap was created. That's information we could store in the mgr module, but that makes it somewhat more awkward. Having this in xattr metadata would be useful and consistent (and accessible through standard CLI tools and calls). (e.g., even if the free-form-ish description wasn't populated automatically, the MDS could auto-fill the timestamp and uid/host that triggered the snap.) Thus we ended up thinking that the immutable flag might belong in there as well. But since there is a dedicated file attribute for that, I agree that this flag is a better fit. Regards, Lars -- SUSE Linux GmbH, GF: Felix Imendörffer, Mary Higgins, Sri Rasiah, HRB 21284 (AG Nürnberg) "Architects should open possibilities and not determine everything." (Ueli Zbinden)