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Subject: Re: [PATCH 2/4] SUNRPC: Clean up xdr_write_pages()
From:   Jeff Layton <jlayton@kernel.org>
To:     Chuck Lever <chuck.lever@oracle.com>, linux-nfs@vger.kernel.org
Date:   Mon, 12 Dec 2022 11:53:27 -0500
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On Sat, 2022-11-26 at 15:55 -0500, Chuck Lever wrote:
> Make it more evident how xdr_write_pages() updates the tail buffer
> by using the convention of naming the iov pointer variable "tail".
> I spent more than a couple of hours chasing through code to
> understand this, so someone is likely to find this useful later.
>=20
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
>  net/sunrpc/xdr.c |   22 +++++++++++++---------
>  1 file changed, 13 insertions(+), 9 deletions(-)
>=20
> diff --git a/net/sunrpc/xdr.c b/net/sunrpc/xdr.c
> index 336a7c7833e4..f7767bf22406 100644
> --- a/net/sunrpc/xdr.c
> +++ b/net/sunrpc/xdr.c
> @@ -1224,30 +1224,34 @@ EXPORT_SYMBOL(xdr_restrict_buflen);
>  /**
>   * xdr_write_pages - Insert a list of pages into an XDR buffer for sendi=
ng
>   * @xdr: pointer to xdr_stream
> - * @pages: list of pages
> - * @base: offset of first byte
> - * @len: length of data in bytes
> + * @pages: array of pages to insert
> + * @base: starting offset of first data byte in @pages
> + * @len: number of data bytes in @pages to insert
>   *
> + * After the @pages are added, the tail iovec is instantiated pointing t=
o
> + * end of the head buffer, and the stream is set up to encode subsequent
> + * items into the tail.
>   */
>  void xdr_write_pages(struct xdr_stream *xdr, struct page **pages, unsign=
ed int base,
>  		 unsigned int len)
>  {
>  	struct xdr_buf *buf =3D xdr->buf;
> -	struct kvec *iov =3D buf->tail;
> +	struct kvec *tail =3D buf->tail;
> +
>  	buf->pages =3D pages;
>  	buf->page_base =3D base;
>  	buf->page_len =3D len;
> =20
> -	iov->iov_base =3D (char *)xdr->p;
> -	iov->iov_len  =3D 0;
> -	xdr->iov =3D iov;
> +	tail->iov_base =3D xdr->p;
> +	tail->iov_len =3D 0;
> +	xdr->iov =3D tail;
> =20
>  	if (len & 3) {
>  		unsigned int pad =3D 4 - (len & 3);
> =20
>  		BUG_ON(xdr->p >=3D xdr->end);
> -		iov->iov_base =3D (char *)xdr->p + (len & 3);
> -		iov->iov_len  +=3D pad;
> +		tail->iov_base =3D (char *)xdr->p + (len & 3);
> +		tail->iov_len +=3D pad;
>  		len +=3D pad;
>  		*xdr->p++ =3D 0;
>  	}
>=20
>=20

Reviewed-by: Jeff Layton <jlayton@kernel.org>