Re: [PATCH v5 3/8] tap: refactor packets handling functions

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

[-- Attachment #1: Type: text/plain, Size: 7968 bytes --]

On Wed, Jun 12, 2024 at 12:09:50AM +0200, Stefano Brivio wrote:
> On Wed,  5 Jun 2024 17:21:24 +0200
> Laurent Vivier <lvivier@redhat.com> wrote:
> 
> > Consolidate pool_tap4() and pool_tap6() into pool_flush_all(),
> > and tap4_handler() and tap6_handler() into tap_handler_all().
> > Create a generic packet_add_all() to consolidate packet
> > addition logic and reduce code duplication.
> > 
> > The purpose is to ease the export of these functions to use
> > them with the vhost-user backend.
> > 
> > Signed-off-by: Laurent Vivier <lvivier@redhat.com>
> > ---
> >  tap.c | 113 +++++++++++++++++++++++++++++++++-------------------------
> >  tap.h |   7 ++++
> >  2 files changed, 71 insertions(+), 49 deletions(-)
> > 
> > diff --git a/tap.c b/tap.c
> > index 2ea08491a51f..5fb3cb83f3d2 100644
> > --- a/tap.c
> > +++ b/tap.c
> > @@ -920,6 +920,61 @@ append:
> >  	return in->count;
> >  }
> >  
> > +/**
> > + * pool_flush() - Flush both IPv4 and IPv6 packet pools
> > + */
> > +void pool_flush_all(void)
> > +{
> > +	pool_flush(pool_tap4);
> > +	pool_flush(pool_tap6);
> > +}
> > +
> > +/**
> > + * tap_handler_all() - IPv4/IPv4 and ARP packet handler for tap file descriptor
> 
> IPv4/IPv6
> 
> > + * @c:		Execution context
> > + * @now:	Current timestamp
> > + */
> > +void tap_handler_all(struct ctx *c, const struct timespec *now)
> 
> I wonder if this shouldn't be named tap_handler() instead. As we
> already have tap_handler_passt() and tap_handler_pasta(), it's not
> immediately clear what "all" refers to.

I concur, I think tap_handler() is a better name.

> > +{
> > +	tap4_handler(c, pool_tap4, now);
> > +	tap6_handler(c, pool_tap6, now);
> > +}
> > +
> > +/**
> > + * packet_add_all_do() - Add a packet to the appropriate TAP pool
> 
> A couple of remarks here:
> 
> - it's a bit unexpected that this is still in tap.c (it adds packets to
>   a pool, it should be in packet.c judging by this name/description).
>   If we call it tap_queue_packet(), then it probably makes more sense?
> 
> - this does more than adding a packet to a pool. It's probably useless
>   to describe in detail what this does, as the function body is anyway
>   rather short and clear, but the current description could be a bit
>   misleading. What about "Queue/capture packet, update notion of
>   guest MAC address"?

So, given this, I think it does make more sense for this to be in
tap.c than packet.c.  How about calling it tap_add_packets().

> - what happens if you just call packet_add() from here, without dealing
>   with 'func' and 'line'? I think it's fine to print in tracing output
>   name and lines from this function, instead of the ones from the
>   caller. It's obvious who the caller is

It is as of this patch, but I believe the idea is this will also be
called from VU code down the line.

> > + * @c:		Execution context
> > + * @l2len:	Total L2 packet length
> > + * @p:		Packet buffer
> > + * @func:	For tracing: name of calling function, NULL means no trace()
> > + * @line:	For tracing: caller line of function call
> > + */
> > +void packet_add_all_do(struct ctx *c, ssize_t l2len, char *p,
> > +		       const char *func, int line)
> > +{
> > +	const struct ethhdr *eh;
> > +
> > +	pcap(p, l2len);
> > +
> > +	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, l2len, p, func, line);
> > +		break;
> > +	case ETH_P_IPV6:
> > +		packet_add_do(pool_tap6, l2len, p, func, line);
> > +		break;
> > +	default:
> > +		break;
> > +	}
> > +}
> > +
> >  /**
> >   * tap_sock_reset() - Handle closing or failure of connect AF_UNIX socket
> >   * @c:		Execution context
> > @@ -946,7 +1001,6 @@ 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;
> >  
> > @@ -959,8 +1013,7 @@ 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) {
> > @@ -987,38 +1040,18 @@ redo:
> >  		/* Complete the partial read above before discarding a malformed
> >  		 * frame, otherwise the stream will be inconsistent.
> >  		 */
> > -		if (l2len < (ssize_t)sizeof(*eh) ||
> > +		if (l2len < (ssize_t)sizeof(struct ethhdr) ||
> >  		    l2len > (ssize_t)ETH_MAX_MTU)
> >  			goto next;
> >  
> > -		pcap(p, l2len);
> > -
> > -		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, l2len, p);
> > -			break;
> > -		case ETH_P_IPV6:
> > -			packet_add(pool_tap6, l2len, p);
> > -			break;
> > -		default:
> > -			break;
> > -		}
> > +		packet_add_all(c, l2len, p);
> >  
> >  next:
> >  		p += l2len;
> >  		n -= l2len;
> >  	}
> >  
> > -	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)
> > @@ -1043,35 +1076,18 @@ 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;
> > @@ -1082,8 +1098,7 @@ 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 2285a87093f9..3ffb7d6c3a91 100644
> > --- a/tap.h
> > +++ b/tap.h
> > @@ -70,5 +70,12 @@ void tap_handler_passt(struct ctx *c, uint32_t events,
> >  		       const struct timespec *now);
> >  int tap_sock_unix_open(char *sock_path);
> >  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_all_do(struct ctx *c, ssize_t l2len, char *p,
> > +		       const char *func, int line);
> > +#define packet_add_all(p, l2len, start)					\
> > +	packet_add_all_do(p, l2len, start, __func__, __LINE__)
> >  
> >  #endif /* TAP_H */
> 

-- 
David Gibson			| 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

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]