Re: [PATCH v15 00/22] Richacls (Core and Ext4)

From: J. Bruce Fields
Date: Tue Nov 10 2015 - 14:17:52 EST

On Tue, Nov 10, 2015 at 06:58:19PM +0100, Andreas Gruenbacher wrote:
> On Tue, Nov 10, 2015 at 6:07 PM, J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote:
> > On Tue, Nov 10, 2015 at 10:43:46AM -0600, Steve French wrote:
> >> I don't have strong disagreement with using pseudo-xattrs to
> >> store/retrieve ACLs (we already do this) but retrieving/setting an ACL
> >> all at once can be awkward when ACLs are quite large e.g. when it
> >> encodes to over 1MB
> >
> > At least in the NFS case, that's also a limitation of the protocol.
> I couldn't find a limit in the NFSv4 specification, but the client and
> server implementations both define arbitrary ACL size limits. In
> addition, the xattr syscalls allow attributes to be up to 64k long.

I don't recall 4.0 specifying any limit, 4.1 does include negotiation of
maximum rpc calls and replies, and that effectively limits ACL sizes
since they have to fit in a single rpc.

> The bigger problem would be incrementally setting ACLs. To prevent
> processes from racing with each other, we would need a locking
> mechanism. In addition, the memory overhead would be prohibitive and
> access decisions would become extremely slow; we would have to come up
> with mechanisms to avoid those problems.

Right. Anyway, not worth the trouble, I think.

(Though what might be worth thinking about at some point is just making
sure we fail in helpful ways.)

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