From: Chuck Lever <cel@kernel.org>
To: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
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 21:31:04 -0400 [thread overview]
Message-ID: <ZG1o2LFiRekz/pMy@manet.1015granger.net> (raw)
In-Reply-To: <4b9c7386-c2b1-2eb7-d248-ddfdc3c2cd1f@embeddedor.com>
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.
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
> > >
next prev parent reply other threads:[~2023-05-24 1:31 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 [this message]
2023-05-24 1:42 ` Gustavo A. R. Silva
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