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Message-ID: <87egpqtmjd.fsf@rustcorp.com.au> Date: Mon, 16 Feb 2015 16:39:42 +1030 From: Rusty Russell <rusty@...tcorp.com.au> To: "Michael S. Tsirkin" <mst@...hat.com> Cc: lkml <linux-kernel@...r.kernel.org>, "netdev\@vger.kernel.org" <netdev@...r.kernel.org> Subject: Re: [PATCH 3/5] virtio: Don't expose legacy net features when VIRTIO_NET_NO_LEGACY defined. "Michael S. Tsirkin" <mst@...hat.com> writes: >> struct virtio_net_hdr hdr; >> __virtio16 num_buffers; /* Number of merged rx buffers */ >> }; >> +#else /* ... VIRTIO_NET_NO_LEGACY */ >> +/* >> + * This header comes first in the scatter-gather list. If you don't >> + * specify GSO or CSUM features, you can simply ignore the header. >> + * >> + * This is bitwise-equivalent to the legacy struct virtio_net_hdr_mrg_rxbuf. > > I would add "but with all fields squashed into the main structure". Yep. >> + */ >> +struct virtio_net_hdr_v1 { >> +#define VIRTIO_NET_HDR_F_NEEDS_CSUM 1 /* Use csum_start, csum_offset */ >> +#define VIRTIO_NET_HDR_F_DATA_VALID 2 /* Csum is valid */ >> + __u8 flags; >> +#define VIRTIO_NET_HDR_GSO_NONE 0 /* Not a GSO frame */ >> +#define VIRTIO_NET_HDR_GSO_TCPV4 1 /* GSO frame, IPv4 TCP (TSO) */ >> +#define VIRTIO_NET_HDR_GSO_UDP 3 /* GSO frame, IPv4 UDP (UFO) */ >> +#define VIRTIO_NET_HDR_GSO_TCPV6 4 /* GSO frame, IPv6 TCP */ >> +#define VIRTIO_NET_HDR_GSO_ECN 0x80 /* TCP has ECN set */ >> + __u8 gso_type; >> + __virtio16 hdr_len; /* Ethernet + IP + tcp/udp hdrs */ >> + __virtio16 gso_size; /* Bytes to append to hdr_len per frame */ >> + __virtio16 csum_start; /* Position to start checksumming from */ >> + __virtio16 csum_offset; /* Offset after that to place checksum */ >> + __virtio16 num_buffers; /* Number of merged rx buffers */ >> +}; >> +#endif /* ...VIRTIO_NET_NO_LEGACY */ > > I note that this way host code can't be structured like this: > > > struct virtio_net_hdr_v1 modern; > /* handle modern guests */ > .... > > #ifndef VIRTIO_NET_NO_LEGACY > struct virtio_net_hdr_mrg_rxbuf mrg; > /* handle legacy guests */ > > #endif > > > Define virtio_net_hdr_v1 unconditionally? Thanks, that's a good idea! Here's the incremental: virtio_net: unconditionally define struct virtio_net_hdr_v1. This was introduced in commit ed9ecb0415b97b5f9f91f146e1977bb372c74c6d, but only defined if !VIRTIO_NET_NO_LEGACY. We should always define it: easier for users to have conditional legacy code. Suggested-by: "Michael S. Tsirkin" <mst@...hat.com> Signed-off-by: Rusty Russell <rusty@...tcorp.com.au> diff --git a/include/uapi/linux/virtio_net.h b/include/uapi/linux/virtio_net.h index 4a9b58113d6e..7bbee79ca293 100644 --- a/include/uapi/linux/virtio_net.h +++ b/include/uapi/linux/virtio_net.h @@ -74,39 +74,12 @@ struct virtio_net_config { __u16 max_virtqueue_pairs; } __attribute__((packed)); -#ifndef VIRTIO_NET_NO_LEGACY -/* This header comes first in the scatter-gather list. - * For legacy virtio, if VIRTIO_F_ANY_LAYOUT is not negotiated, it must - * be the first element of the scatter-gather list. If you don't - * specify GSO or CSUM features, you can simply ignore the header. */ -struct virtio_net_hdr { -#define VIRTIO_NET_HDR_F_NEEDS_CSUM 1 // Use csum_start, csum_offset -#define VIRTIO_NET_HDR_F_DATA_VALID 2 // Csum is valid - __u8 flags; -#define VIRTIO_NET_HDR_GSO_NONE 0 // Not a GSO frame -#define VIRTIO_NET_HDR_GSO_TCPV4 1 // GSO frame, IPv4 TCP (TSO) -#define VIRTIO_NET_HDR_GSO_UDP 3 // GSO frame, IPv4 UDP (UFO) -#define VIRTIO_NET_HDR_GSO_TCPV6 4 // GSO frame, IPv6 TCP -#define VIRTIO_NET_HDR_GSO_ECN 0x80 // TCP has ECN set - __u8 gso_type; - __virtio16 hdr_len; /* Ethernet + IP + tcp/udp hdrs */ - __virtio16 gso_size; /* Bytes to append to hdr_len per frame */ - __virtio16 csum_start; /* Position to start checksumming from */ - __virtio16 csum_offset; /* Offset after that to place checksum */ -}; - -/* This is the version of the header to use when the MRG_RXBUF - * feature has been negotiated. */ -struct virtio_net_hdr_mrg_rxbuf { - struct virtio_net_hdr hdr; - __virtio16 num_buffers; /* Number of merged rx buffers */ -}; -#else /* ... VIRTIO_NET_NO_LEGACY */ /* * This header comes first in the scatter-gather list. If you don't * specify GSO or CSUM features, you can simply ignore the header. * - * This is bitwise-equivalent to the legacy struct virtio_net_hdr_mrg_rxbuf. + * This is bitwise-equivalent to the legacy struct virtio_net_hdr_mrg_rxbuf, + * only flattened. */ struct virtio_net_hdr_v1 { #define VIRTIO_NET_HDR_F_NEEDS_CSUM 1 /* Use csum_start, csum_offset */ @@ -124,6 +97,29 @@ struct virtio_net_hdr_v1 { __virtio16 csum_offset; /* Offset after that to place checksum */ __virtio16 num_buffers; /* Number of merged rx buffers */ }; + +#ifndef VIRTIO_NET_NO_LEGACY +/* This header comes first in the scatter-gather list. + * For legacy virtio, if VIRTIO_F_ANY_LAYOUT is not negotiated, it must + * be the first element of the scatter-gather list. If you don't + * specify GSO or CSUM features, you can simply ignore the header. */ +struct virtio_net_hdr { + /* See VIRTIO_NET_HDR_F_* */ + __u8 flags; + /* See VIRTIO_NET_HDR_GSO_* */ + __u8 gso_type; + __virtio16 hdr_len; /* Ethernet + IP + tcp/udp hdrs */ + __virtio16 gso_size; /* Bytes to append to hdr_len per frame */ + __virtio16 csum_start; /* Position to start checksumming from */ + __virtio16 csum_offset; /* Offset after that to place checksum */ +}; + +/* This is the version of the header to use when the MRG_RXBUF + * feature has been negotiated. */ +struct virtio_net_hdr_mrg_rxbuf { + struct virtio_net_hdr hdr; + __virtio16 num_buffers; /* Number of merged rx buffers */ +}; #endif /* ...VIRTIO_NET_NO_LEGACY */ /* -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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