Re: [PATCH v2 10/20] udp: Convert to iov_tail

[David Gibson <david@gibson.dropbear.id.au>]

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On Fri, Apr 11, 2025 at 03:10:20PM +0200, Laurent Vivier wrote:
> Use packet_base() 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 9e3786e6efe8..d09e51190d54 100644
> --- a/iov.c
> +++ b/iov.c
> @@ -175,7 +175,6 @@ size_t iov_size(const struct iovec *iov, size_t iov_cnt)
>   *		 iov array, a negative value if there is no enough room in the
>   *		 destination iov array
>   */
> -/* cppcheck-suppress unusedFunction */
>  int iov_slice(struct iovec *dst_iov, size_t dst_iov_cnt,
>  	      const struct iovec *iov, size_t iov_cnt,
>  	      size_t offset, size_t *bytes)
> diff --git a/udp.c b/udp.c
> index ab3e9d20fd74..75526f743994 100644
> --- a/udp.c
> +++ b/udp.c
> @@ -862,15 +862,20 @@ 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;
>  	uint8_t topif;
>  	socklen_t sl;
>  
>  	ASSERT(!c->no_udp);
>  
> -	uh = packet_get(p, idx, 0, sizeof(*uh), NULL);
> +	if (!packet_base(p, idx, &data))
> +		return 1;
> +
> +	uh = IOV_PEEK_HEADER(&data, uhc);
>  	if (!uh)
>  		return 1;
>  
> @@ -907,23 +912,30 @@ 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_base(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 len;

Variables named 'len' or similar are usually byte counts, not item
counts.  So maybe a different name here?

> +
> +			len = iov_slice(&m[j], UIO_MAXIOV - j,
> +				        &data.iov[0], data.cnt, data.off, NULL);

Might be nice to have a wrapper around iov_slice() that turns the
whole of an iov_tail into a new plain iov.

> +			if (len < 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 = len;
> +			j += len;
>  		} else {
>  			mm[i].msg_hdr.msg_iov = NULL;
>  			mm[i].msg_hdr.msg_iovlen = 0;

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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