Re: [PATCH 3/3] tap: add die() on vhost error

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

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On Tue, Apr 01, 2025 at 01:38:09PM +0200, Eugenio Pérez wrote:
> In case the kernel needs to signal an error.
> 
> Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> ---
>  epoll_type.h |  2 ++
>  passt.c      |  4 ++++
>  passt.h      |  1 +
>  tap.c        | 16 ++++++++++++++++
>  4 files changed, 23 insertions(+)
> 
> diff --git a/epoll_type.h b/epoll_type.h
> index 6284c79..6b320db 100644
> --- a/epoll_type.h
> +++ b/epoll_type.h
> @@ -46,6 +46,8 @@ enum epoll_type {
>  	EPOLL_TYPE_REPAIR,
>  	/* vhost-kernel call socket */
>  	EPOLL_TYPE_VHOST_CALL,
> +	/* vhost-kernel error socket */
> +	EPOLL_TYPE_VHOST_ERROR,
> 
>  	EPOLL_NUM_TYPES,
>  };
> diff --git a/passt.c b/passt.c
> index 19c5d5f..2779e0b 100644
> --- a/passt.c
> +++ b/passt.c
> @@ -80,6 +80,7 @@ char *epoll_type_str[] = {
>  	[EPOLL_TYPE_REPAIR_LISTEN]	= "TCP_REPAIR helper listening socket",
>  	[EPOLL_TYPE_REPAIR]		= "TCP_REPAIR helper socket",
>  	[EPOLL_TYPE_VHOST_CALL]		= "vhost-kernel call socket",
> +	[EPOLL_TYPE_VHOST_ERROR]	= "vhost-kernel error socket",
>  };
>  static_assert(ARRAY_SIZE(epoll_type_str) == EPOLL_NUM_TYPES,
>  	      "epoll_type_str[] doesn't match enum epoll_type");
> @@ -361,6 +362,9 @@ loop:
>  		case EPOLL_TYPE_VHOST_CALL:
>  			vhost_call_cb(&c, ref, &now);
>  			break;
> +		case EPOLL_TYPE_VHOST_ERROR:
> +			die("Error on vhost-kernel socket");
> +			break;
>  		default:
>  			/* Can't happen */
>  			ASSERT(0);
> diff --git a/passt.h b/passt.h
> index eb5aa03..9e42f3b 100644
> --- a/passt.h
> +++ b/passt.h
> @@ -307,6 +307,7 @@ struct ctx {
> 
>  		int kick_fd;
>  		int call_fd;
> +		int err_fd;
>  	} vq[2];
> 
>  	int no_dns;
> diff --git a/tap.c b/tap.c
> index fbe83aa..b02d3da 100644
> --- a/tap.c
> +++ b/tap.c
> @@ -1552,6 +1552,22 @@ static int tap_ns_tun(void *arg)
>  		if (rc < 0)
>  			die_perror("Failed to add call eventfd to epoll");
>  		c->vq[i].call_fd = file.fd;
> +
> +		file.fd = eventfd(0, EFD_NONBLOCK | EFD_CLOEXEC);
> +		if (file.fd < 0)
> +			die_perror("Failed to create error eventfd");
> +
> +		rc = ioctl(vhost_fd, VHOST_SET_VRING_ERR, &file);
> +		if (rc < 0)
> +			die_perror(
> +				"VHOST_SET_VRING_ERR ioctl on /dev/vhost-net failed");
> +
> +		ref.type = EPOLL_TYPE_VHOST_ERROR, ref.fd = file.fd;
> +		ev.data.u64 = ref.u64;
> +		rc = epoll_ctl(c->epollfd, EPOLL_CTL_ADD, ref.fd, &ev);
> +		if (rc < 0)
> +			die_perror("Failed to add error eventfd to epoll");
> +		c->vq[i].err_fd = file.fd;

If it's possible to re-initialize vhost, eventually it would be nice
to do so eventually, but for now die()ing is perfectly reasonable.

>  	}
> 
>  	/* 1:1 translation */

-- 
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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