Re: [PATCH v5 10/29] udp: Convert to iov_tail

[Stefano Brivio <sbrivio@redhat.com>]

On Thu, 17 Apr 2025 18:51:17 +0200
Laurent Vivier <lvivier@redhat.com> wrote:

> Use packet_data() and extract headers using IOV_REMOVE_HEADER()
> and IOV_PEEK_HEADER() rather than packet_get().
> 
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>
> ---
>  iov.c |  1 -
>  udp.c | 34 +++++++++++++++++++++++-----------
>  2 files changed, 23 insertions(+), 12 deletions(-)
> 
> diff --git a/iov.c b/iov.c
> index bb095634246e..3e18040d22a8 100644
> --- a/iov.c
> +++ b/iov.c
> @@ -389,7 +389,6 @@ void *iov_remove_header_(struct iov_tail *tail, void *v, size_t len, size_t alig
>   *		 iov array, a negative value if there is not enough room in the
>   *		 destination iov array
>   */
> -/* cppcheck-suppress unusedFunction */
>  int iov_tail_slice(struct iovec *dst_iov, size_t dst_iov_cnt,
>                     struct iov_tail *tail, size_t *bytes)
>  {
> diff --git a/udp.c b/udp.c
> index 40af7dfc260f..27e31bc5d92d 100644
> --- a/udp.c
> +++ b/udp.c
> @@ -872,15 +872,20 @@ int udp_tap_handler(const struct ctx *c, uint8_t pif,
>  	struct iovec m[UIO_MAXIOV];
>  	const struct udphdr *uh;
>  	struct udp_flow *uflow;
> -	int i, s, count = 0;
> +	int i, j, s, count = 0;
> +	struct iov_tail data;
>  	flow_sidx_t tosidx;
>  	in_port_t src, dst;
> +	struct udphdr uhc;

I'm struggling to understand what the 'c' in 'uhc' stands for
("contiguous"?), but given that it's used just twice, what about making
it a bit longer, say, 'uh_storage'?

>  	uint8_t topif;
>  	socklen_t sl;
>  
>  	ASSERT(!c->no_udp);
>  
> -	uh = packet_get(p, idx, 0, sizeof(*uh), NULL);
> +	if (!packet_data(p, idx, &data))
> +		return 1;
> +
> +	uh = IOV_PEEK_HEADER(&data, uhc);
>  	if (!uh)
>  		return 1;
>  
> @@ -917,23 +922,30 @@ int udp_tap_handler(const struct ctx *c, uint8_t pif,
>  
>  	pif_sockaddr(c, &to_sa, &sl, topif, &toside->eaddr, toside->eport);
>  
> -	for (i = 0; i < (int)p->count - idx; i++) {
> -		struct udphdr *uh_send;
> -		size_t len;
> +	for (i = 0, j = 0; i < (int)p->count - idx && j < UIO_MAXIOV; i++) {
> +		const struct udphdr *uh_send;
>  
> -		uh_send = packet_get(p, idx + i, 0, sizeof(*uh), &len);
> +		if (!packet_data(p, idx + i, &data))
> +			return p->count - idx;
> +
> +		uh_send = IOV_REMOVE_HEADER(&data, uhc);
>  		if (!uh_send)
>  			return p->count - idx;
>  
>  		mm[i].msg_hdr.msg_name = &to_sa;
>  		mm[i].msg_hdr.msg_namelen = sl;
>  
> -		if (len) {
> -			m[i].iov_base = (char *)(uh_send + 1);
> -			m[i].iov_len = len;
> +		if (data.cnt) {
> +			int cnt;
> +
> +			cnt = iov_tail_slice(&m[j], UIO_MAXIOV - j,
> +					     &data, NULL);
> +			if (cnt < 0)
> +				return p->count - idx;
>  
> -			mm[i].msg_hdr.msg_iov = m + i;
> -			mm[i].msg_hdr.msg_iovlen = 1;
> +			mm[i].msg_hdr.msg_iov = &m[j];
> +			mm[i].msg_hdr.msg_iovlen = cnt;
> +			j += cnt;
>  		} else {
>  			mm[i].msg_hdr.msg_iov = NULL;
>  			mm[i].msg_hdr.msg_iovlen = 0;

-- 
Stefano