Re: [PATCH 8/9] epoll: Split listening Unix domain socket into its own type

[Stefano Brivio <sbrivio@redhat.com>]

On Mon,  7 Aug 2023 23:46:30 +1000
David Gibson <david@gibson.dropbear.id.au> wrote:

> tap_handler() actually handles events on three different types of object:
> the /dev/tap character device (pasta), a connected Unix domain socket
> (passt) or a listening Unix domain socket (passt).
> 
> The last, in particular, really has no handling in common with the others,
> so split it into its own epoll type and directly dispatch to the relevant
> handler from the top level.
> 
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> ---
>  passt.c |  6 +++++-
>  passt.h |  6 ++++--
>  tap.c   | 20 ++++++++------------
>  tap.h   |  4 ++--
>  4 files changed, 19 insertions(+), 17 deletions(-)
> 
> diff --git a/passt.c b/passt.c
> index c32981d..c60f346 100644
> --- a/passt.c
> +++ b/passt.c
> @@ -64,6 +64,7 @@ char *epoll_type_str[EPOLL_TYPE_MAX+1] = {
>  	[EPOLL_TYPE_ICMPV6]	= "ICMPv6 socket",
>  	[EPOLL_TYPE_NSQUIT]	= "namespace inotify",
>  	[EPOLL_TYPE_TAP]	= "tap device",
> +	[EPOLL_TYPE_TAP_LISTEN]	= "listening qemu socket",
>  };
>  
>  /**
> @@ -317,7 +318,10 @@ loop:
>  
>  		switch (ref.type) {
>  		case EPOLL_TYPE_TAP:
> -			tap_handler(&c, ref.fd, events[i].events, &now);
> +			tap_handler(&c, events[i].events, &now);
> +			break;
> +		case EPOLL_TYPE_TAP_LISTEN:
> +			tap_listen_handler(&c, eventmask);
>  			break;
>  		case EPOLL_TYPE_NSQUIT:
>  			pasta_netns_quit_handler(&c, quit_fd);
> diff --git a/passt.h b/passt.h
> index 176bc85..7dae08b 100644
> --- a/passt.h
> +++ b/passt.h
> @@ -61,10 +61,12 @@ enum epoll_type {
>  	EPOLL_TYPE_ICMPV6,
>  	/* inotify fd watching for end of netns (pasta) */
>  	EPOLL_TYPE_NSQUIT,
> -	/* tap char device, or qemu socket fd */
> +	/* tap char device, or connected qemu socket fd */
>  	EPOLL_TYPE_TAP,
> +	/* socket listening for qemu socket connections */
> +	EPOLL_TYPE_TAP_LISTEN,
>  
> -	EPOLL_TYPE_MAX = EPOLL_TYPE_TAP,
> +	EPOLL_TYPE_MAX = EPOLL_TYPE_TAP_LISTEN,
>  };
>  
>  /**
> diff --git a/tap.c b/tap.c
> index ad0decf..8468f86 100644
> --- a/tap.c
> +++ b/tap.c
> @@ -1076,7 +1076,7 @@ restart:
>  static void tap_sock_unix_init(struct ctx *c)
>  {
>  	int fd = socket(AF_UNIX, SOCK_STREAM, 0);
> -	union epoll_ref ref = { .type = EPOLL_TYPE_TAP };
> +	union epoll_ref ref = { .type = EPOLL_TYPE_TAP_LISTEN };
>  	struct epoll_event ev = { 0 };
>  	struct sockaddr_un addr = {
>  		.sun_family = AF_UNIX,
> @@ -1142,10 +1142,11 @@ static void tap_sock_unix_init(struct ctx *c)
>  }
>  
>  /**
> - * tap_sock_unix_new() - Handle new connection on listening socket
> + * tap_listen_handler() - Handle new connection on listening socket
>   * @c:		Execution context
> + * @events:	epoll events on the socket
>   */
> -static void tap_sock_unix_new(struct ctx *c)
> +void tap_listen_handler(struct ctx *c, uint32_t events)
>  {
>  	union epoll_ref ref = { .type = EPOLL_TYPE_TAP };
>  	struct epoll_event ev = { 0 };
> @@ -1153,6 +1154,9 @@ static void tap_sock_unix_new(struct ctx *c)
>  	struct ucred ucred;
>  	socklen_t len;
>  
> +	if (events != EPOLLIN)
> +		return;
> +

This comment actually belongs to 2/4 of the tap reset clean-up series,
but posting it here for clarity: ...wouldn't it be appropriate to
handle errors while at it? Otherwise I guess we'll just spin on
EPOLLERR or EPOLLRDHUP.

I didn't realise before that other series that we didn't actually
handle errors on this path -- that's the reason why error handling is
missing, nothing else.

The rest of the series looks good to me, thanks -- waiting for v2.

-- 
Stefano