Re: Bugs / Patch in nfsd

[Albert Fluegel <af@muc.de>]

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On Mon, Nov 18, 2013 at 12:37:31PM -0500, J. Bruce Fields wrote:
> > > Anyway, absent objections my default is to queue this up for 3.14 (using
> > > S_IALLUGO).
This is great ! Thank you.

> > > ...
> One problem he's seeing was RHEL5-specific, the other is the known ext4
> problem that's been discussed before.
> 
> (Basically, ext4 has a tradeoff between correctness, lookup performance,
> and compatibility with some buggy old clients:
> 
> 	1. turn off dir_index and performance on large directories may
> 	   suffer, but it's correct and any client will be happy.
> 	2. turn on dir_index and return 32-bit cookies: now you get
> 	   directory loops on large directories due to random hash
> 	   collisions.
> 	3. turn on dir_index and return 64-bit cookies: some clients seem
> 	   to then return errors to 32-bit applications doing readdirs.
> 	   Cookies have been 64-bit since NFSv3 and 32-bit Linux clients
> 	   deal with this fine (it fakes up its own small integer offsets
> 	   to return to applications), but apparently some other clients
> 	   return errors on readdir.
> 
> So currently we default to 3 and if people complain, tell them to turn
> off dir_index and complain to their client vendor....)
I agree with that. Did some "research" in the meantime. It's a real abyss.
I think it does not make much sense to continue this thread. Thanks to
all contributors bringing more light into this.

So this is for the records:
With current RHEL5/6 + ext3 there is no problem over NFS. With ext4 + dir_index
Solaris-8 fails with EOVERFLOW on a directory read. Solaris-2.5.1 complains
(RPC: Can't decode result). There are 2 differences when turning off dir_index:
The cookies have very low values then (in contrast to using all 64 bits with
dir_index on) and the order returned by readdir is different (does not start
with . and ..) Don't know, which one makes which Solaris fail.
HP-UX fails differently on a ext4, even with dir_index turned off, but not
always. If in the reply of a getattr the nanoseconds are not 0, HPUX fails
with "stale file handle". Could it be, it mixes some of these bytes into
the handle ? If in the reply the nanoseconds are all 0, HPUX works even
with 64 bit cookies (dir_index on) on an ext4. On a xfs they all work.
In the NFS replies on an xfs i've seen all nanoseconds set to 0, so this is
consistent and the faulty behaviour seems definitely on the client side.

- AF

-- 
Albert Flügel
Lindwurmstraße 51
80337 München
Telefon: +49-89-2010895
Telefon: +49-170-5665444
E-Mail: af@muc.de
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