Re: [PATCH 13/24] tap: export pool_flush()/tapX_handler()/packet_add()

[Stefano Brivio <sbrivio@redhat.com>]

On Fri,  2 Feb 2024 15:11:40 +0100
Laurent Vivier <lvivier@redhat.com> wrote:

> From: Laurent Vivier <laurent@vivier.eu>
> 
> Signed-off-by: Laurent Vivier <laurent@vivier.eu>
> ---
>  tap.c | 98 +++++++++++++++++++++++++++++------------------------------
>  tap.h |  7 +++++
>  2 files changed, 56 insertions(+), 49 deletions(-)

I'm assuming that you need this patch to recycle those bits of "tap"
functions for usage in vhost-user code... which shows they actually
have little to do with tun/tap interfaces.

But sure, we already have there stuff to deal with UNIX domain sockets,
so "tap" is already somewhat inconsistent.

If use "tap" for a (long) moment to denote "anything guest/container
facing", then:

> diff --git a/tap.c b/tap.c
> index 29f389057ac1..5b1b61550c13 100644
> --- a/tap.c
> +++ b/tap.c
> @@ -911,6 +911,45 @@ append:
>  	return in->count;
>  }
>  
> +void pool_flush_all(void)

I think that the "all" in pool_flush_all() doesn't really convey the
message of "all pools", and tap_pools_flush() would describe this
better.

All these would need function comments, by the way.

> +{
> +	pool_flush(pool_tap4);
> +	pool_flush(pool_tap6);
> +}
> +
> +void tap_handler_all(struct ctx *c, const struct timespec *now)

Same here: something like tap_pools_handler() describes better the fact
that this is not handling "everything", rather "tap pools".

> +{
> +	tap4_handler(c, pool_tap4, now);
> +	tap6_handler(c, pool_tap6, now);
> +}
> +
> +void packet_add_all_do(struct ctx *c, ssize_t len, char *p,
> +		       const char *func, int line)

...and this doesn't add "all the packets" -- it adds just one, to one
pool! What about tap_pool_add()?

About using packet_add_do() directly, and passing in 'line': I'm not
sure there's a big advantage in having the line from
tap_handler_passt() or another caller reported instead of having the
point where packet_add() is actually called.

There might also be an issue in this function (packet_add_all_do()) so
one might want to start debugging there.

> +{
> +	const struct ethhdr *eh;
> +
> +	pcap(p, len);
> +
> +	eh = (struct ethhdr *)p;
> +
> +	if (memcmp(c->mac_guest, eh->h_source, ETH_ALEN)) {
> +		memcpy(c->mac_guest, eh->h_source, ETH_ALEN);
> +		proto_update_l2_buf(c->mac_guest, NULL);
> +	}
> +
> +	switch (ntohs(eh->h_proto)) {
> +	case ETH_P_ARP:
> +	case ETH_P_IP:
> +		packet_add_do(pool_tap4, len, p, func, line);
> +		break;
> +	case ETH_P_IPV6:
> +		packet_add_do(pool_tap6, len, p, func, line);
> +		break;
> +	default:
> +		break;
> +	}
> +}
> +
>  /**
>   * tap_sock_reset() - Handle closing or failure of connect AF_UNIX socket
>   * @c:		Execution context
> @@ -937,7 +976,6 @@ static void tap_sock_reset(struct ctx *c)
>  void tap_handler_passt(struct ctx *c, uint32_t events,
>  		       const struct timespec *now)
>  {
> -	const struct ethhdr *eh;
>  	ssize_t n, rem;
>  	char *p;
>  
> @@ -950,8 +988,7 @@ redo:
>  	p = pkt_buf;
>  	rem = 0;
>  
> -	pool_flush(pool_tap4);
> -	pool_flush(pool_tap6);
> +	pool_flush_all();
>  
>  	n = recv(c->fd_tap, p, TAP_BUF_FILL, MSG_DONTWAIT);
>  	if (n < 0) {
> @@ -978,37 +1015,18 @@ redo:
>  		/* Complete the partial read above before discarding a malformed
>  		 * frame, otherwise the stream will be inconsistent.
>  		 */
> -		if (len < (ssize_t)sizeof(*eh) || len > (ssize_t)ETH_MAX_MTU)
> +		if (len < (ssize_t)sizeof(struct ethhdr) ||
> +		    len > (ssize_t)ETH_MAX_MTU)
>  			goto next;
>  
> -		pcap(p, len);
> -
> -		eh = (struct ethhdr *)p;
> -
> -		if (memcmp(c->mac_guest, eh->h_source, ETH_ALEN)) {
> -			memcpy(c->mac_guest, eh->h_source, ETH_ALEN);
> -			proto_update_l2_buf(c->mac_guest, NULL);
> -		}
> -
> -		switch (ntohs(eh->h_proto)) {
> -		case ETH_P_ARP:
> -		case ETH_P_IP:
> -			packet_add(pool_tap4, len, p);
> -			break;
> -		case ETH_P_IPV6:
> -			packet_add(pool_tap6, len, p);
> -			break;
> -		default:
> -			break;
> -		}
> +		packet_add_all(c, len, p);
>  
>  next:
>  		p += len;
>  		n -= len;
>  	}
>  
> -	tap4_handler(c, pool_tap4, now);
> -	tap6_handler(c, pool_tap6, now);
> +	tap_handler_all(c, now);
>  
>  	/* We can't use EPOLLET otherwise. */
>  	if (rem)
> @@ -1033,35 +1051,18 @@ void tap_handler_pasta(struct ctx *c, uint32_t events,
>  redo:
>  	n = 0;
>  
> -	pool_flush(pool_tap4);
> -	pool_flush(pool_tap6);
> +	pool_flush_all();
>  restart:
>  	while ((len = read(c->fd_tap, pkt_buf + n, TAP_BUF_BYTES - n)) > 0) {
> -		const struct ethhdr *eh = (struct ethhdr *)(pkt_buf + n);
>  
> -		if (len < (ssize_t)sizeof(*eh) || len > (ssize_t)ETH_MAX_MTU) {
> +		if (len < (ssize_t)sizeof(struct ethhdr) ||
> +		    len > (ssize_t)ETH_MAX_MTU) {
>  			n += len;
>  			continue;
>  		}
>  
> -		pcap(pkt_buf + n, len);
>  
> -		if (memcmp(c->mac_guest, eh->h_source, ETH_ALEN)) {
> -			memcpy(c->mac_guest, eh->h_source, ETH_ALEN);
> -			proto_update_l2_buf(c->mac_guest, NULL);
> -		}
> -
> -		switch (ntohs(eh->h_proto)) {
> -		case ETH_P_ARP:
> -		case ETH_P_IP:
> -			packet_add(pool_tap4, len, pkt_buf + n);
> -			break;
> -		case ETH_P_IPV6:
> -			packet_add(pool_tap6, len, pkt_buf + n);
> -			break;
> -		default:
> -			break;
> -		}
> +		packet_add_all(c, len, pkt_buf + n);
>  
>  		if ((n += len) == TAP_BUF_BYTES)
>  			break;
> @@ -1072,8 +1073,7 @@ restart:
>  
>  	ret = errno;
>  
> -	tap4_handler(c, pool_tap4, now);
> -	tap6_handler(c, pool_tap6, now);
> +	tap_handler_all(c, now);
>  
>  	if (len > 0 || ret == EAGAIN)
>  		return;
> diff --git a/tap.h b/tap.h
> index 437b9aa2b43f..7157ef37ee6e 100644
> --- a/tap.h
> +++ b/tap.h
> @@ -82,5 +82,12 @@ void tap_handler_pasta(struct ctx *c, uint32_t events,
>  void tap_handler_passt(struct ctx *c, uint32_t events,
>  		       const struct timespec *now);
>  void tap_sock_init(struct ctx *c);
> +void pool_flush_all(void);
> +void tap_handler_all(struct ctx *c, const struct timespec *now);
> +
> +void packet_add_do(struct pool *p, size_t len, const char *start,
> +		   const char *func, int line);
> +#define packet_add_all(p, len, start)					\
> +	packet_add_all_do(p, len, start, __func__, __LINE__)
>  
>  #endif /* TAP_H */

-- 
Stefano