Re: [PATCH 2/7] udp: Split tap-bound UDP packets into multiple buffers using io vector

[Stefano Brivio <sbrivio@redhat.com>]

On Tue, 30 Apr 2024 20:05:36 +1000
David Gibson <david@gibson.dropbear.id.au> wrote:

> When sending to the tap device, currently we assemble the headers and
> payload into a single contiguous buffer.  Those are described by a single
> struct iovec, then a batch of frames is sent to the device with
> tap_send_frames().
> 
> In order to better integrate the IPv4 and IPv6 paths, we want the IP
> header in a different buffer that might not be contiguous with the
> payload.  To prepare for that, split the UDP packet into an iovec of
> buffers.  We use the same split that Laurent recently introduced for
> TCP for convenience.
> 
> This removes the last use of tap_hdr_len_(), tap_frame_base() and
> tap_frame_len(), so remove those too.
> 
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> ---
>  tap.h | 38 ------------------------------
>  udp.c | 74 +++++++++++++++++++++++++++++++++++++++--------------------
>  2 files changed, 49 insertions(+), 63 deletions(-)
> 
> diff --git a/tap.h b/tap.h
> index 75aa3f03..754703d2 100644
> --- a/tap.h
> +++ b/tap.h
> @@ -43,44 +43,6 @@ static inline void tap_hdr_update(struct tap_hdr *thdr, size_t l2len)
>  	thdr->vnet_len = htonl(l2len);
>  }
>  
> -static inline size_t tap_hdr_len_(const struct ctx *c)
> -{
> -	if (c->mode == MODE_PASST)
> -		return sizeof(struct tap_hdr);
> -	else
> -		return 0;
> -}
> -
> -/**
> - * tap_frame_base() - Find start of tap frame
> - * @c:		Execution context
> - * @taph:	Pointer to tap specific header buffer
> - *
> - * Returns: pointer to the start of tap frame - suitable for an
> - *          iov_base to be passed to tap_send_frames())
> - */
> -static inline void *tap_frame_base(const struct ctx *c, struct tap_hdr *taph)
> -{
> -	return (char *)(taph + 1) - tap_hdr_len_(c);
> -}
> -
> -/**
> - * tap_frame_len() - Finalize tap frame and return total length
> - * @c:		Execution context
> - * @taph:	Tap header to finalize
> - * @plen:	L2 packet length (includes L2, excludes tap specific headers)
> - *
> - * Returns: length of the tap frame including tap specific headers - suitable
> - *          for an iov_len to be passed to tap_send_frames()
> - */
> -static inline size_t tap_frame_len(const struct ctx *c, struct tap_hdr *taph,
> -				   size_t plen)
> -{
> -	if (c->mode == MODE_PASST)
> -		taph->vnet_len = htonl(plen);
> -	return plen + tap_hdr_len_(c);
> -}
> -
>  struct in_addr tap_ip4_daddr(const struct ctx *c);
>  void tap_udp4_send(const struct ctx *c, struct in_addr src, in_port_t sport,
>  		   struct in_addr dst, in_port_t dport,
> diff --git a/udp.c b/udp.c
> index 545212c5..4650b366 100644
> --- a/udp.c
> +++ b/udp.c
> @@ -222,12 +222,28 @@ struct udp6_l2_buf_t {
>  #endif
>  udp6_l2_buf[UDP_MAX_FRAMES];
>  
> +/**
> + * enum udp_iov_idx - Indices for the buffers making up a single UDP frame
> + * @UDP_IOV_TAP         TAP specific header

Nits: s/TAP/tap/ and

> + * @UDP_IOV_ETH         ethernet header

s/ethernet/Ethernet.

-- 
Stefano