Re: [PATCH net-next v2 08/10] crypto: af_alg: Support MSG_SPLICE_PAGES

[Paolo Abeni]

On Tue, 2023-05-30 at 15:16 +0100, David Howells wrote:
> Make AF_ALG sendmsg() support MSG_SPLICE_PAGES.  This causes pages to be
> spliced from the source iterator.
> 
> This allows ->sendpage() to be replaced by something that can handle
> multiple multipage folios in a single transaction.
> 
> Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
> cc: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
> cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
> cc: Eric Dumazet <edumazet@xxxxxxxxxx>
> cc: Jakub Kicinski <kuba@xxxxxxxxxx>
> cc: Paolo Abeni <pabeni@xxxxxxxxxx>
> cc: Jens Axboe <axboe@xxxxxxxxx>
> cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> cc: linux-crypto@xxxxxxxxxxxxxxx
> cc: netdev@xxxxxxxxxxxxxxx
> ---
>  crypto/af_alg.c         | 28 ++++++++++++++++++++++++++--
>  crypto/algif_aead.c     | 22 +++++++++++-----------
>  crypto/algif_skcipher.c |  8 ++++----
>  3 files changed, 41 insertions(+), 17 deletions(-)
> 
> diff --git a/crypto/af_alg.c b/crypto/af_alg.c
> index fd56ccff6fed..62f4205d42e3 100644
> --- a/crypto/af_alg.c
> +++ b/crypto/af_alg.c
> @@ -940,6 +940,10 @@ int af_alg_sendmsg(struct socket *sock, struct msghdr *msg, size_t size,
>  	bool init = false;
>  	int err = 0;
>  
> +	if ((msg->msg_flags & MSG_SPLICE_PAGES) &&
> +	    !iov_iter_is_bvec(&msg->msg_iter))
> +		return -EINVAL;
> +
>  	if (msg->msg_controllen) {
>  		err = af_alg_cmsg_send(msg, &con);
>  		if (err)
> @@ -985,7 +989,7 @@ int af_alg_sendmsg(struct socket *sock, struct msghdr *msg, size_t size,
>  	while (size) {
>  		struct scatterlist *sg;
>  		size_t len = size;
> -		size_t plen;
> +		ssize_t plen;
>  
>  		/* use the existing memory in an allocated page */
>  		if (ctx->merge) {
> @@ -1030,7 +1034,27 @@ int af_alg_sendmsg(struct socket *sock, struct msghdr *msg, size_t size,
>  		if (sgl->cur)
>  			sg_unmark_end(sg + sgl->cur - 1);
>  
> -		if (1 /* TODO check MSG_SPLICE_PAGES */) {
> +		if (msg->msg_flags & MSG_SPLICE_PAGES) {
> +			struct sg_table sgtable = {
> +				.sgl		= sg,
> +				.nents		= sgl->cur,
> +				.orig_nents	= sgl->cur,
> +			};
> +
> +			plen = extract_iter_to_sg(&msg->msg_iter, len, &sgtable,
> +						  MAX_SGL_ENTS, 0);

It looks like the above expect/supports only ITER_BVEC iterators, what
about adding a WARN_ON_ONCE(<other iov type>)?

Also, I'm keeping this series a bit more in pw to allow Herbert or
others to have a look.

Cheers,

Paolo