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Date:   Tue, 2 Mar 2021 15:45:20 -0500
To:     Chuck Lever <chuck.lever@oracle.com>
Cc:     linux-nfs@vger.kernel.org
Subject: Re: [PATCH v1 12/42] NFSD: Update the NFSv3 FSSTAT3res encoder to
 use struct xdr_stream
Message-ID: <20210302204520.GF3400@fieldses.org>
References: <161461145466.8508.13379815439337754427.stgit@klimt.1015granger.net>
 <161461179102.8508.11890812651210896607.stgit@klimt.1015granger.net>
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From:   bfields@fieldses.org (J. Bruce Fields)
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On Mon, Mar 01, 2021 at 10:16:31AM -0500, Chuck Lever wrote:
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
>  fs/nfsd/nfs3xdr.c |   58 ++++++++++++++++++++++++++++++++++++++++-------------
>  1 file changed, 44 insertions(+), 14 deletions(-)
> 
> diff --git a/fs/nfsd/nfs3xdr.c b/fs/nfsd/nfs3xdr.c
> index e159e4557428..e4a569e7216d 100644
> --- a/fs/nfsd/nfs3xdr.c
> +++ b/fs/nfsd/nfs3xdr.c
> @@ -17,6 +17,13 @@
>  #define NFSDDBG_FACILITY		NFSDDBG_XDR
>  
>  
> +/*
> + * Force construction of an empty post-op attr
> + */
> +static const struct svc_fh nfs3svc_null_fh = {
> +	.fh_no_wcc	= true,
> +};
> +
>  /*
>   * Mapping of S_IF* types to NFS file types
>   */
> @@ -1392,27 +1399,50 @@ nfs3svc_encode_entry_plus(void *cd, const char *name,
>  	return encode_entry(cd, name, namlen, offset, ino, d_type, 1);
>  }
>  
> +static bool
> +svcxdr_encode_fsstat3resok(struct xdr_stream *xdr,
> +			   const struct nfsd3_fsstatres *resp)
> +{
> +	const struct kstatfs *s = &resp->stats;
> +	u64 bs = s->f_bsize;
> +	__be32 *p;
> +
> +	p = xdr_reserve_space(xdr, XDR_UNIT * 13);
> +	if (!p)
> +		return false;
> +	p = xdr_encode_hyper(p, bs * s->f_blocks);	/* total bytes */
> +	p = xdr_encode_hyper(p, bs * s->f_bfree);	/* free bytes */
> +	p = xdr_encode_hyper(p, bs * s->f_bavail);	/* user available bytes */
> +	p = xdr_encode_hyper(p, s->f_files);		/* total inodes */
> +	p = xdr_encode_hyper(p, s->f_ffree);		/* free inodes */
> +	p = xdr_encode_hyper(p, s->f_ffree);		/* user available inodes */
> +	*p = cpu_to_be32(resp->invarsec);		/* mean unchanged time */
> +
> +	return true;
> +}
> +
>  /* FSSTAT */
>  int
>  nfs3svc_encode_fsstatres(struct svc_rqst *rqstp, __be32 *p)
>  {
> +	struct xdr_stream *xdr = &rqstp->rq_res_stream;
>  	struct nfsd3_fsstatres *resp = rqstp->rq_resp;
> -	struct kstatfs	*s = &resp->stats;
> -	u64		bs = s->f_bsize;
>  
> -	*p++ = resp->status;
> -	*p++ = xdr_zero;	/* no post_op_attr */
> -
> -	if (resp->status == 0) {
> -		p = xdr_encode_hyper(p, bs * s->f_blocks);	/* total bytes */
> -		p = xdr_encode_hyper(p, bs * s->f_bfree);	/* free bytes */
> -		p = xdr_encode_hyper(p, bs * s->f_bavail);	/* user available bytes */
> -		p = xdr_encode_hyper(p, s->f_files);	/* total inodes */
> -		p = xdr_encode_hyper(p, s->f_ffree);	/* free inodes */
> -		p = xdr_encode_hyper(p, s->f_ffree);	/* user available inodes */
> -		*p++ = htonl(resp->invarsec);	/* mean unchanged time */
> +	if (!svcxdr_encode_nfsstat3(xdr, resp->status))
> +		return 0;
> +	switch (resp->status) {
> +	case nfs_ok:
> +		if (!svcxdr_encode_post_op_attr(rqstp, xdr, &nfs3svc_null_fh))
> +			return 0;
> +		if (!svcxdr_encode_fsstat3resok(xdr, resp))
> +			return 0;
> +		break;
> +	default:
> +		if (!svcxdr_encode_post_op_attr(rqstp, xdr, &nfs3svc_null_fh))
> +			return 0;

Dumb question: will this result in the same xdr on the wire as the above
that just hard-coded xdr_zero?

I feel like there's a lot of biolerplate error handling.  In the v4 case
I centralized some of it after a fuzzer found an oops in some of that
copy-pasted boilerplate:

	b7571e4cd39a nfsd4: skip encoder in trivial error cases
	bac966d60652 nfsd4: individual encoders no longer see error cases

I dunno, maybe that was overkill.

--b.

>  	}
> -	return xdr_ressize_check(rqstp, p);
> +
> +	return 1;
>  }
>  
>  /* FSINFO */
>