On Tue, Feb 21, 2017 at 10:21:05PM +0100, Andreas Gruenbacher wrote: > On Tue, Feb 21, 2017 at 7:46 PM, Chuck Lever <chuck.lever@xxxxxxxxxx> wrote: > > Hi Andreas- > > > > > >> On Feb 20, 2017, at 4:31 PM, Andreas Gruenbacher <agruenba@xxxxxxxxxx> wrote: > >> > >> On Mon, Feb 20, 2017 at 6:15 PM, J. Bruce Fields <bfields@xxxxxxxxxx> wrote: > >>> On Mon, Feb 20, 2017 at 11:42:31AM -0500, Chuck Lever wrote: > >>>> > >>>>> On Feb 20, 2017, at 11:09 AM, J. Bruce Fields <bfields@xxxxxxxxxx> wrote: > >>>>> > >>>>> On Sun, Feb 19, 2017 at 02:29:03PM -0500, Chuck Lever wrote: > >>>>>> > >>>>>>> On Feb 18, 2017, at 9:07 PM, J. Bruce Fields <bfields@xxxxxxxxxx> wrote: > >>>>>>> > >>>>>>> From: Weston Andros Adamson <dros@xxxxxxxxxx> > >>>>>>> > >>>>>>> Instead of preallocating pags, allow xdr_partial_copy_from_skb() to > >>>>>>> allocate whatever pages we need on demand. This is what the NFSv3 ACL > >>>>>>> code does. > >>>>>> > >>>>>> The patch description does not explain why this change is > >>>>>> being done. > >>>>> > >>>>> The only justification I see is avoiding allocating pages unnecessarily. > >>>> > >>>> That makes sense. Is there a real world workload that has seen > >>>> a negative effect? > >>>> > >>>> > >>>>> Without this patch, for each getacl, we allocate 17 pages (if I'm > >>>>> calculating correctly) and probably rarely use most of them. > >>>>> > >>>>> In the v3 case I think it's 7 pages instead of 17. > >>>> > >>>> I would have guessed 9. Out of curiosity, is there a reason > >>>> documented for these size limits? > >>> > >>> > >>> In the v4 case: > >>> > >>> #define NFS4ACL_MAXPAGES DIV_ROUND_UP(XATTR_SIZE_MAX, PAGE_SIZE) > >>> > >>> And I believe XATTR_SIZE_MAX is a global maximum on the size of any > >>> extend attribute value. > >> > >> XATTR_SIZE_MAX is the maximum size of an extended attribute. NFSv4 > >> ACLs are passed through unchanged in "system.nfs4_acl". > > > > "Extended attribute" means this is a Linux-specific limit? > > Yes. > > > Is there anything that prevents a non-Linux system from constructing > > or returning an ACL that is larger than that? > > No. In the >=v4.1 case there are session limits, but they'll typically be less. In the 4.0 case I think there's no explicit limit at all. In practice I bet other systems are similar to Linux in that the assume peers won't send rpc replies or requests larger than about the maximum-sized read or write. But again that'll usually be a higher limit than our ACL limit. > > What happens on a Linux client when a server returns an ACL that does > > not fit in this allotment? > > I would hope an error, but I haven't tested it. I haven't tested either, but it looks to me like the rpc layer receives a truncated request, the xdr decoding recognizes that it's truncated, and the result is an -ERANGE. Looking now I think that my "NFSv4: simplify getacl decoding" changes that to an -EIO. More importantly, it makes that an EIO even when the calling application was only asking for the length, not the actual ACL data. I'll fix that. --b. -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
