From: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
To: Chuck Lever <cel@kernel.org>
Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>,
Chuck Lever <chuck.lever@oracle.com>,
Jeff Layton <jlayton@kernel.org>,
linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-hardening@vger.kernel.org, dai.ngo@oracle.com
Subject: Re: [PATCH][next] nfsd: Replace one-element array with flexible-array member
Date: Tue, 23 May 2023 19:42:20 -0600 [thread overview]
Message-ID: <136d72e5-287c-ebaf-c1e1-92b10e68ba8d@embeddedor.com> (raw)
In-Reply-To: <ZG1o2LFiRekz/pMy@manet.1015granger.net>
On 5/23/23 19:31, Chuck Lever wrote:
> On Tue, May 23, 2023 at 07:11:37PM -0600, Gustavo A. R. Silva wrote:
>>
>> On 5/23/23 19:01, Chuck Lever wrote:
>>> On Tue, May 23, 2023 at 06:44:23PM -0600, Gustavo A. R. Silva wrote:
>>>> One-element arrays are deprecated, and we are replacing them with
>>>> flexible array members instead. So, replace a one-element array
>>>> with a flexible-arrayº member in struct vbi_anc_data and refactor
>>>
>>> I don't know what "struct vbi_anc_data" is. Is the patch description
>>> correct?
>>
>> Oops, copy/paste error. I'll fix it up. :)
>>
>>>
>>>
>>>> the rest of the code, accordingly.
>>>>
>>>> This results in no differences in binary output.
>>>>
>>>> Link: https://github.com/KSPP/linux/issues/79
>>>> Link: https://github.com/KSPP/linux/issues/298
>>>> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
>>>
>>>> ---
>>>> fs/nfsd/nfs4callback.c | 2 +-
>>>> fs/nfsd/xdr4.h | 2 +-
>>>> 2 files changed, 2 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/fs/nfsd/nfs4callback.c b/fs/nfsd/nfs4callback.c
>>>> index 4039ffcf90ba..2c688d51135d 100644
>>>> --- a/fs/nfsd/nfs4callback.c
>>>> +++ b/fs/nfsd/nfs4callback.c
>>>> @@ -353,7 +353,7 @@ encode_cb_recallany4args(struct xdr_stream *xdr,
>>>> {
>>>> encode_nfs_cb_opnum4(xdr, OP_CB_RECALL_ANY);
>>>> encode_uint32(xdr, ra->ra_keep);
>>>> - encode_bitmap4(xdr, ra->ra_bmval, ARRAY_SIZE(ra->ra_bmval));
>>>> + encode_bitmap4(xdr, ra->ra_bmval, 1);
>>>
>>> I find the new code less self-documenting.
>>>
>>>
>>>> hdr->nops++;
>>>> }
>>>> diff --git a/fs/nfsd/xdr4.h b/fs/nfsd/xdr4.h
>>>> index 510978e602da..68072170eac8 100644
>>>> --- a/fs/nfsd/xdr4.h
>>>> +++ b/fs/nfsd/xdr4.h
>>>> @@ -899,7 +899,7 @@ struct nfsd4_operation {
>>>> struct nfsd4_cb_recall_any {
>>>> struct nfsd4_callback ra_cb;
>>>> u32 ra_keep;
>>>> - u32 ra_bmval[1];
>>>> + u32 ra_bmval[];
>>>
>>> This is not a placeholder for "1 or more elements". We actually want
>>> just a single u32 element in this array. Doesn't this change the
>>> sizeof(struct nfsd4_cb_recall_any) ?
>>
>> I see. Yes, it does change the size. Can we replace it with a simple
>> object of type u32? or do you actually need this to stay an array?
>
> It's not impossible to make it a scalar u32, however...
>
> In this area of code, *_bmval is always a bitmap -- an array of u32s.
> Helpers like encode_bitmap4() assume an array. I think it would be
> less confusing overall to human readers if it remained an array.
>
> In this case, it is a single element array because CB_RECALL_ANY
> doesn't happen to use bits above the first 32-bit word of the
> bitmap.
I see. If this is never going to be treated as a flexible array, then
it can stay as is.
-fstrict-flex-arrays=3 should not warn about this because the array
will never ever be tried to be accessed beyond element 1. :)
Thanks for the feedback!
--
Gustavo
>
> We could make it a 2-element array, I think, without harm. Send a
> patch for that, and Dai can test it to make sure there are no
> unexpected interoperability consequences.
>
> I hope that would avoid suspicious-looking array definitions.
>
>
>>>> };
>>>> #endif
>>>> --
>>>> 2.34.1
>>>>
prev parent reply other threads:[~2023-05-24 4:39 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-24 0:44 [PATCH][next] nfsd: Replace one-element array with flexible-array member Gustavo A. R. Silva
2023-05-24 1:01 ` Chuck Lever
2023-05-24 1:11 ` Gustavo A. R. Silva
2023-05-24 1:31 ` Chuck Lever
2023-05-24 1:42 ` Gustavo A. R. Silva [this message]
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