Re: [dpdk-dev] [PATCH 01/28] vhost: introduce vhost transport operations structure

[Aaron Conole <aconole@redhat.com>]

Nikos Dragazis <ndragazis@arrikto.com> writes:

> This is the first of a series of patches, whose purpose is to add
> support for the virtio-vhost-user transport. This is a vhost-user
> transport implementation that is different from the default AF_UNIX
> transport. It uses the virtio-vhost-user PCI device in order to tunnel
> vhost-user protocol messages over virtio. This lets guests act as vhost
> device backends for other guests.
>
> File descriptor passing is specific to the AF_UNIX vhost-user protocol
> transport.  In order to add support for additional transports, it is
> necessary to extract transport-specific code from the main vhost-user
> code.
>
> This patch introduces struct vhost_transport_ops and associates each
> device with a transport.  Core vhost-user code calls into
> vhost_transport_ops to perform transport-specific operations.
>
> Notifying callfd is a transport-specific operation, so it belongs to
> trans_af_unix.c.
>
> Several more patches follow this one to complete the task of moving
> AF_UNIX transport code out of core vhost-user code.
>
> Signed-off-by: Nikos Dragazis <ndragazis@arrikto.com>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---

You'll need to also accommodate the meson build - probably with
something like:

diff --git a/lib/librte_vhost/meson.build b/lib/librte_vhost/meson.build
index 3090bbe08..81b70683b 100644
--- a/lib/librte_vhost/meson.build
+++ b/lib/librte_vhost/meson.build
@@ -14,6 +14,6 @@ allow_experimental_apis = true
 cflags += '-fno-strict-aliasing'
 sources = files('fd_man.c', 'iotlb.c', 'socket.c', 'vdpa.c',
                'vhost.c', 'vhost_user.c',
-               'virtio_net.c', 'vhost_crypto.c')
+               'virtio_net.c', 'vhost_crypto.c', 'trans_af_unix.c')
 headers = files('rte_vhost.h', 'rte_vdpa.h', 'rte_vhost_crypto.h')
 deps += ['ethdev', 'cryptodev', 'hash', 'pci']


>  lib/librte_vhost/Makefile        |  2 +-
>  lib/librte_vhost/trans_af_unix.c | 20 ++++++++++++++++++++
>  lib/librte_vhost/vhost.c         |  1 +
>  lib/librte_vhost/vhost.h         | 34 +++++++++++++++++++++++++++++-----
>  4 files changed, 51 insertions(+), 6 deletions(-)
>  create mode 100644 lib/librte_vhost/trans_af_unix.c
>
> diff --git a/lib/librte_vhost/Makefile b/lib/librte_vhost/Makefile
> index 8623e91..5ff5fb2 100644
> --- a/lib/librte_vhost/Makefile
> +++ b/lib/librte_vhost/Makefile
> @@ -23,7 +23,7 @@ LDLIBS += -lrte_eal -lrte_mempool -lrte_mbuf -lrte_ethdev -lrte_net
>  
>  # all source are stored in SRCS-y
>  SRCS-$(CONFIG_RTE_LIBRTE_VHOST) := fd_man.c iotlb.c socket.c vhost.c \
> -					vhost_user.c virtio_net.c vdpa.c
> +					vhost_user.c virtio_net.c vdpa.c trans_af_unix.c
>  
>  # install includes
>  SYMLINK-$(CONFIG_RTE_LIBRTE_VHOST)-include += rte_vhost.h rte_vdpa.h
> diff --git a/lib/librte_vhost/trans_af_unix.c b/lib/librte_vhost/trans_af_unix.c
> new file mode 100644
> index 0000000..3f0c308
> --- /dev/null
> +++ b/lib/librte_vhost/trans_af_unix.c
> @@ -0,0 +1,20 @@
> +/* SPDX-License-Identifier: BSD-3-Clause
> + * Copyright(c) 2010-2018 Intel Corporation
> + * Copyright(c) 2017 Red Hat, Inc.
> + * Copyright(c) 2019 Arrikto Inc.
> + */
> +
> +#include "vhost.h"
> +
> +static int
> +af_unix_vring_call(struct virtio_net *dev __rte_unused,
> +		   struct vhost_virtqueue *vq)
> +{
> +	if (vq->callfd >= 0)
> +		eventfd_write(vq->callfd, (eventfd_t)1);
> +	return 0;
> +}
> +
> +const struct vhost_transport_ops af_unix_trans_ops = {
> +	.vring_call = af_unix_vring_call,
> +};
> diff --git a/lib/librte_vhost/vhost.c b/lib/librte_vhost/vhost.c
> index 981837b..a36bc01 100644
> --- a/lib/librte_vhost/vhost.c
> +++ b/lib/librte_vhost/vhost.c
> @@ -507,6 +507,7 @@ vhost_new_device(void)
>  	dev->vid = i;
>  	dev->flags = VIRTIO_DEV_BUILTIN_VIRTIO_NET;
>  	dev->slave_req_fd = -1;
> +	dev->trans_ops = &af_unix_trans_ops;
>  	dev->vdpa_dev_id = -1;
>  	dev->postcopy_ufd = -1;
>  	rte_spinlock_init(&dev->slave_req_lock);
> diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
> index 884befa..077f213 100644
> --- a/lib/librte_vhost/vhost.h
> +++ b/lib/librte_vhost/vhost.h
> @@ -286,6 +286,30 @@ struct guest_page {
>  	uint64_t size;
>  };
>  
> +struct virtio_net;
> +
> +/**
> + * A structure containing function pointers for transport-specific operations.
> + */
> +struct vhost_transport_ops {
> +	/**
> +	 * Notify the guest that used descriptors have been added to the vring.
> +	 * The VRING_AVAIL_F_NO_INTERRUPT flag and event idx have already been checked
> +	 * so this function just needs to perform the notification.
> +	 *
> +	 * @param dev
> +	 *  vhost device
> +	 * @param vq
> +	 *  vhost virtqueue
> +	 * @return
> +	 *  0 on success, -1 on failure
> +	 */
> +	int (*vring_call)(struct virtio_net *dev, struct vhost_virtqueue *vq);
> +};
> +
> +/** The traditional AF_UNIX vhost-user protocol transport. */
> +extern const struct vhost_transport_ops af_unix_trans_ops;
> +
>  /**
>   * Device structure contains all configuration information relating
>   * to the device.
> @@ -312,6 +336,7 @@ struct virtio_net {
>  	uint16_t		mtu;
>  
>  	struct vhost_device_ops const *notify_ops;
> +	struct vhost_transport_ops const *trans_ops;
>  
>  	uint32_t		nr_guest_pages;
>  	uint32_t		max_guest_pages;
> @@ -544,12 +569,11 @@ vhost_vring_call_split(struct virtio_net *dev, struct vhost_virtqueue *vq)
>  		if ((vhost_need_event(vhost_used_event(vq), new, old) &&
>  					(vq->callfd >= 0)) ||
>  				unlikely(!signalled_used_valid))
> -			eventfd_write(vq->callfd, (eventfd_t) 1);
> +			dev->trans_ops->vring_call(dev, vq);
>  	} else {
>  		/* Kick the guest if necessary. */
> -		if (!(vq->avail->flags & VRING_AVAIL_F_NO_INTERRUPT)
> -				&& (vq->callfd >= 0))
> -			eventfd_write(vq->callfd, (eventfd_t)1);
> +		if (!(vq->avail->flags & VRING_AVAIL_F_NO_INTERRUPT))
> +			dev->trans_ops->vring_call(dev, vq);
>  	}
>  }
>  
> @@ -601,7 +625,7 @@ vhost_vring_call_packed(struct virtio_net *dev, struct vhost_virtqueue *vq)
>  		kick = true;
>  kick:
>  	if (kick)
> -		eventfd_write(vq->callfd, (eventfd_t)1);
> +		dev->trans_ops->vring_call(dev, vq);
>  }
>  
>  static __rte_always_inline void