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From:   Chuck Lever <chuck.lever@oracle.com>
To:     Bruce Fields <bfields@fieldses.org>
CC:     Linux NFS Mailing List <linux-nfs@vger.kernel.org>
Subject: Re: [PATCH v1 19/42] SUNRPC: Fix xdr_get_next_encode_buffer() page
 boundary handling
Thread-Topic: [PATCH v1 19/42] SUNRPC: Fix xdr_get_next_encode_buffer() page
 boundary handling
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Date:   Wed, 3 Mar 2021 18:42:33 +0000
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> On Mar 3, 2021, at 1:38 PM, Bruce Fields <bfields@fieldses.org> wrote:
>=20
> On Wed, Mar 03, 2021 at 06:30:40PM +0000, Chuck Lever wrote:
>>=20
>>=20
>>> On Mar 3, 2021, at 1:27 PM, Chuck Lever <chuck.lever@oracle.com> wrote:
>>>=20
>>>=20
>>>=20
>>>> On Mar 3, 2021, at 1:25 PM, Bruce Fields <bfields@fieldses.org> wrote:
>>>>=20
>>>> On Wed, Mar 03, 2021 at 06:19:33PM +0000, Chuck Lever wrote:
>>>>>=20
>>>>>=20
>>>>>> On Mar 3, 2021, at 11:52 AM, Bruce Fields <bfields@fieldses.org> wro=
te:
>>>>>>=20
>>>>>> On Wed, Mar 03, 2021 at 03:43:28PM +0000, Chuck Lever wrote:
>>>>>>> Why would that not be OK? the next call to xdr_get_next_encode_buff=
er()
>>>>>>> should do the right thing and bounce the new encoded data from the
>>>>>>> next page into this one again.
>>>>>>>=20
>>>>>>> So far I have not encountered any problems. Would such a problem sh=
ow
>>>>>>> up with some frequency under normal use, or would it be especially
>>>>>>> subtle?
>>>>>>=20
>>>>>> I mainly just want to make sure we've got a coherent idea what this =
code
>>>>>> is doing....
>>>>>=20
>>>>> Agreed, that's a good thing.
>>>>=20
>>>> I'm also a little vague on what exactly the problem is you're running
>>>> into.  (Probably because I haven't really looked at the v3 readdir
>>>> encoding.)
>>>>=20
>>>> Is it approaching the end of a page, or is it running out of buflen?
>>>> How exactly does it fail?
>>>=20
>>> I don't recall exactly, it was a late last summer when I wrote all thes=
e.
>>>=20
>>> Approaching the end of a page, IIRC, the unpatched code would leave
>>> a gap in the directory entry stream.
>>=20
>> Well, when I converted the entry encoders to use xdr_stream, it would
>> have a problem around the end of a page. The existing encoders are
>> open-coded to deal with this case.
>=20
> We're not seeing v4 readdir bugs, though, I wonder what's different?

It's a small patch, easy to revert and find out with your own preferred
tests.


--
Chuck Lever