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Subject: Re: [PATCH v2 1/2] SUNRPC: Keep buf->len in sync with xdr->nwords
 when expanding holes
From:   Chuck Lever <chuck.lever@oracle.com>
In-Reply-To: <20201208202925.597663-2-Anna.Schumaker@Netapp.com>
Date:   Tue, 8 Dec 2020 15:56:16 -0500
Cc:     Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
        Anna Schumaker <Anna.Schumaker@Netapp.com>
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Message-Id: <2A6797DD-246D-4994-B38C-57AA0196D061@oracle.com>
References: <20201208202925.597663-1-Anna.Schumaker@Netapp.com>
 <20201208202925.597663-2-Anna.Schumaker@Netapp.com>
To:     Anna Schumaker <schumaker.anna@gmail.com>
Precedence: bulk


> On Dec 8, 2020, at 3:29 PM, schumaker.anna@gmail.com wrote:
>=20
> From: Anna Schumaker <Anna.Schumaker@Netapp.com>
>=20
> Otherwise we could end up placing data a few bytes off from where we
> actually want to put it.
>=20
> Fixes: 84ce182ab85b "SUNRPC: Add the ability to expand holes in data =
pages"
> Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
> ---
> net/sunrpc/xdr.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>=20
> diff --git a/net/sunrpc/xdr.c b/net/sunrpc/xdr.c
> index 71e03b930b70..5b848fe65c81 100644
> --- a/net/sunrpc/xdr.c
> +++ b/net/sunrpc/xdr.c
> @@ -1314,6 +1314,7 @@ uint64_t xdr_expand_hole(struct xdr_stream *xdr, =
uint64_t offset, uint64_t lengt
> 		unsigned int res =3D _shift_data_right_tail(buf, from + =
bytes - shift, shift);
> 		truncated =3D shift - res;
> 		xdr->nwords -=3D XDR_QUADLEN(truncated);
> +		buf->len -=3D 4 * XDR_QUADLEN(truncated);

If I understand what you're doing here correctly, the usual idiom
is "XDR_QUADLEN(truncated) << 2" .


> 		bytes -=3D shift;
> 	}
>=20
> @@ -1325,7 +1326,7 @@ uint64_t xdr_expand_hole(struct xdr_stream *xdr, =
uint64_t offset, uint64_t lengt
> 					bytes);
> 	_zero_pages(buf->pages, buf->page_base + offset, length);
>=20
> -	buf->len +=3D length - (from - offset) - truncated;
> +	buf->len +=3D length - (from - offset);
> 	xdr_set_page(xdr, offset + length, PAGE_SIZE);
> 	return length;
> }
> --=20
> 2.29.2
>=20

--
Chuck Lever