On Mon, Dec 05, 2016 at 04:36:03PM +0100, Miklos Szeredi wrote: > On Mon, Dec 5, 2016 at 4:19 PM, J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote: > >> Can NFS people comment on this? Where does the nfs4_acl come from? > > > > This is the interface the NFS client provides for applications to modify > > NFSv4 ACLs on servers that support them. > > Fine, but why are we seeing this xattr on exports where no xattrs are > set on the exported fs? I don't know. I took another look at the original patch and don't see any details on the server setup: which server is it (knfsd, ganesha, netapp, ...)? How is it configured? > >> What can overlayfs do if it's a non-empty ACL? > > > > As little as possible. You can't copy it up, can you? So any attempt > > to support it is going to be incomplete. > > Right. > > > > >> Does knfsd translate posix ACL into NFS acl? If so, we can translate > >> back. Should we do a generic POSIX<->NFS acl translator? > > > > knsd does translate between POSIX and NFSv4 ACLs. It's a complicated > > This does explain the nfs4_acl xattr on the client. Question: if it's > empty, why have it at all? I'm honestly not sure what's going on there. I'd be curious to see a network trace if possible. > > algorithm, and lossy (in the NFSv4->POSIX direction). The client > > developers have been understandably reluctant to have anything to do > > with it. > > > > So, I think listxattr should omit system.nfs4_acl, and attempts to > > set/get the attribute should error out. The same should apply to any > > "system." attribute not supported by both filesystems, I think? > > Basically that's what happens now. The problem is that nfsv4 mounts > seem always have these xattrs, even when the exported fs doesn't have > anything. I said "both", that's a logical "and". Whether or not nfs claims support would then be irrelevant in this case, since ext4 doesn't support system.nfs4_acl. > We could do the copy up even if the NFS4->POSIX translation was > possible (which is the case with POSIX ACL translated by knfsd). We'd > just get back the original ACL, so that's OK. Note that knfsd is an exception, most NFSv4-acl-supporting servers aren't translating from POSIX ACLs. > NFS is only supported as lower (read-only) layer, so we don't care > about changing the ACL on the server. Out of curiosity, how do you check permissions after copy up? The client doesn't do much permissions-checking normally, because it's hard to get right--even in the absence of ACLs, it may not understand the server's owners and groups completely. I guess that's fine, you may be happy to let people write to the file without permissions to the lower file, since the writes aren't going there anyway. So, I don't know what want here. You're not going to want to use the ACL for actual permission-checking, and you can't modify it, so it doesn't seem very useful. --b. -- To unsubscribe from this list: send the line "unsubscribe linux-unionfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
