On Tue, Feb 21, 2017 at 10:37 PM, J. Bruce Fields <bfields@xxxxxxxxxx> wrote: > 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. Just be careful not to return a length from getxattr(path, name, NULL, 0) that will cause getxattr(path, name, buffer, size) to fail with ERANGE, please. Otherwise, user space might get very confused. Thanks, Andreas -- 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
