Re: [PATCH] net/virtio-user: check negotiated features before set

[Tiwei Bie <tiwei.bie@intel.com>]

On Thu, Aug 09, 2018 at 01:34:55PM -0500, Allain Legacy wrote:
> From: eric zhang <eric.zhang@windriver.com>
> 
> This patch checks negotiated features to see if necessary to offload
> before set the tap device offload capabilities. It also checks if kernel
> support the TUNSETOFFLOAD operation.
> 
> Signed-off-by: eric zhang <eric.zhang@windriver.com>
> Signed-off-by: Allain Legacy <allain.legacy@windriver.com>
> ---
>  drivers/net/virtio/virtio_user/vhost_kernel.c     |  2 +-
>  drivers/net/virtio/virtio_user/vhost_kernel_tap.c | 56 +++++++++++++++++------
>  drivers/net/virtio/virtio_user/vhost_kernel_tap.h |  2 +-
>  3 files changed, 44 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/net/virtio/virtio_user/vhost_kernel.c b/drivers/net/virtio/virtio_user/vhost_kernel.c
> index b2444096c..66f2eaca9 100644
> --- a/drivers/net/virtio/virtio_user/vhost_kernel.c
> +++ b/drivers/net/virtio/virtio_user/vhost_kernel.c
> @@ -339,7 +339,7 @@ vhost_kernel_enable_queue_pair(struct virtio_user_dev *dev,
>  		hdr_size = sizeof(struct virtio_net_hdr);
>  
>  	tapfd = vhost_kernel_open_tap(&dev->ifname, hdr_size, req_mq,
> -			 (char *)dev->mac_addr);
> +			 (char *)dev->mac_addr, dev->features);
>  	if (tapfd < 0) {
>  		PMD_DRV_LOG(ERR, "fail to open tap for vhost kernel");
>  		return -1;
> diff --git a/drivers/net/virtio/virtio_user/vhost_kernel_tap.c b/drivers/net/virtio/virtio_user/vhost_kernel_tap.c
> index 9ea7ade74..eda9fb78c 100644
> --- a/drivers/net/virtio/virtio_user/vhost_kernel_tap.c
> +++ b/drivers/net/virtio/virtio_user/vhost_kernel_tap.c
> @@ -16,21 +16,54 @@
>  
>  #include "vhost_kernel_tap.h"
>  #include "../virtio_logs.h"
> +#include "../virtio_pci.h"
> +
> +static int
> +vhost_kernel_tap_set_offload(int fd, uint64_t feature)
> +{
> +	unsigned int offload = 0;
> +
> +	if (feature & (1ULL << VIRTIO_NET_F_GUEST_CSUM))
> +		offload |= TUN_F_CSUM;
> +	if (feature & (1ULL << VIRTIO_NET_F_GUEST_TSO4))
> +		offload |= TUN_F_TSO4;
> +	if (feature & (1ULL << VIRTIO_NET_F_GUEST_TSO6))
> +		offload |= TUN_F_TSO6;
> +	if (feature & ((1ULL << VIRTIO_NET_F_GUEST_TSO4) |
> +		(1ULL << VIRTIO_NET_F_GUEST_TSO6)) &&
> +		(feature & (1ULL << VIRTIO_NET_F_GUEST_ECN)))
> +		offload |= TUN_F_TSO_ECN;
> +	if (feature & (1ULL << VIRTIO_NET_F_GUEST_UFO))
> +		offload |= TUN_F_UFO;
> +
> +	if (offload != 0) {
> +		/* Check if our kernel supports TUNSETOFFLOAD */
> +		if (ioctl(fd, TUNSETOFFLOAD, 0) != 0 && errno == EINVAL) {
> +			PMD_DRV_LOG(ERR, "Kernel does't support TUNSETOFFLOAD\n");
> +			return -ENOTSUP;
> +		}
> +
> +		if (ioctl(fd, TUNSETOFFLOAD, offload) != 0) {
> +			offload &= ~TUN_F_UFO;
> +			if (ioctl(fd, TUNSETOFFLOAD, offload) != 0) {
> +				PMD_DRV_LOG(ERR, "TUNSETOFFLOAD ioctl() failed: %s\n",
> +					strerror(errno));
> +				return -1;
> +			}
> +		}

I'm not quite sure whether it's a good idea to
return failure when failed to set offloads to
tap. And QEMU also doesn't do this:

https://github.com/qemu/qemu/blob/6ad90805383e/net/tap-linux.c#L261

We should also check whether offloads available
when handling VHOST_GET_FEATURES.

Thanks

> +	}
> +
> +	return 0;
> +}
>  
>  int
>  vhost_kernel_open_tap(char **p_ifname, int hdr_size, int req_mq,
> -			 const char *mac)
> +			 const char *mac, uint64_t features)
>  {
>  	unsigned int tap_features;
>  	int sndbuf = INT_MAX;
>  	struct ifreq ifr;
>  	int tapfd;
> -	unsigned int offload =
> -			TUN_F_CSUM |
> -			TUN_F_TSO4 |
> -			TUN_F_TSO6 |
> -			TUN_F_TSO_ECN |
> -			TUN_F_UFO;
>  
>  	/* TODO:
>  	 * 1. verify we can get/set vnet_hdr_len, tap_probe_vnet_hdr_len
> @@ -90,13 +123,8 @@ vhost_kernel_open_tap(char **p_ifname, int hdr_size, int req_mq,
>  		goto error;
>  	}
>  
> -	/* TODO: before set the offload capabilities, we'd better (1) check
> -	 * negotiated features to see if necessary to offload; (2) query tap
> -	 * to see if it supports the offload capabilities.
> -	 */
> -	if (ioctl(tapfd, TUNSETOFFLOAD, offload) != 0)
> -		PMD_DRV_LOG(ERR, "TUNSETOFFLOAD ioctl() failed: %s",
> -			   strerror(errno));
> +	if (vhost_kernel_tap_set_offload(tapfd, features) != 0)
> +		goto error;
>  
>  	memset(&ifr, 0, sizeof(ifr));
>  	ifr.ifr_hwaddr.sa_family = ARPHRD_ETHER;
> diff --git a/drivers/net/virtio/virtio_user/vhost_kernel_tap.h b/drivers/net/virtio/virtio_user/vhost_kernel_tap.h
> index 01a026f50..e0e95b4f5 100644
> --- a/drivers/net/virtio/virtio_user/vhost_kernel_tap.h
> +++ b/drivers/net/virtio/virtio_user/vhost_kernel_tap.h
> @@ -36,4 +36,4 @@
>  #define PATH_NET_TUN	"/dev/net/tun"
>  
>  int vhost_kernel_open_tap(char **p_ifname, int hdr_size, int req_mq,
> -			 const char *mac);
> +			 const char *mac, uint64_t features);
> -- 
> 2.12.1
>