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Message-ID: <20150924092545.28d3ae52@bahia.local>
Date: Thu, 24 Sep 2015 09:25:45 +0200
From: Greg Kurz <gkurz@...ux.vnet.ibm.com>
To: David Woodhouse <dwmw2@...radead.org>
Cc: David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
rusty@...tcorp.com.au, mst@...hat.com, linux-api@...r.kernel.org,
linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v2] Fix AF_PACKET ABI breakage in 4.2
On Wed, 23 Sep 2015 19:45:08 +0100
David Woodhouse <dwmw2@...radead.org> wrote:
> Commit 7d82410950aa ("virtio: add explicit big-endian support to memory
> accessors") accidentally changed the virtio_net header used by
> AF_PACKET with PACKET_VNET_HDR from host-endian to big-endian.
>
Hi David,
Oops my bad... I obviously overlooked this one when adding cross-endian
support.
> Since virtio_legacy_is_little_endian() is a very long identifier,
> define a VIO_LE macro and use that throughout the code instead of the
VIO usually refers to virtual IO adapters for the PowerPC pSeries platform.
> hard-coded 'false' for little-endian.
>
What about introducing dedicated accessors as it is done in many other
locations where we do virtio byteswap ? Something like:
static inline bool packet_is_little_endian(void)
{
return virtio_legacy_is_little_endian();
}
static inline u16 packet16_to_cpu(__virtio16 val)
{
return __virtio16_to_cpu(packet_is_little_endian(), val);
}
static inline __virtio16 cpu_to_packet16(u16 val)
{
return __cpu_to_virtio16(packet_is_little_endian(), val);
}
It results in prettier code IMHO. Have a look at drivers/net/tun.c or
drivers/vhost/vhost.c.
> This restores the ABI to match 4.1 and earlier kernels, and makes my
> test program work again.
>
BTW, there is still work to do if we want to support cross-endian legacy or
virtio 1 on a big endian arch...
Cheers.
--
Greg
> Signed-off-by: David Woodhouse <David.Woodhouse@...el.com>
> ---
> On Wed, 2015-09-23 at 11:09 -0700, David Miller wrote:
> > > +#define VIO_LE virtio_legacy_is_little_endian()
> >
> > When you define a shorthand macro, the defines to a function call,
> > make the macro have parenthesis too.
>
> In which case I suppose it also wants to be lower-case. Although
> "function call" is a bit strong since it's effectively just a constant.
> I'm still wondering if it'd be nicer just to use (__force u16) instead.
>
> diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
> index 7b8e39a..aa4b15c 100644
> --- a/net/packet/af_packet.c
> +++ b/net/packet/af_packet.c
> @@ -230,6 +230,8 @@ struct packet_skb_cb {
> } sa;
> };
>
> +#define vio_le() virtio_legacy_is_little_endian()
> +
> #define PACKET_SKB_CB(__skb) ((struct packet_skb_cb *)((__skb)->cb))
>
> #define GET_PBDQC_FROM_RB(x) ((struct tpacket_kbdq_core *)(&(x)->prb_bdqc))
> @@ -2680,15 +2682,15 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)
> goto out_unlock;
>
> if ((vnet_hdr.flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) &&
> - (__virtio16_to_cpu(false, vnet_hdr.csum_start) +
> - __virtio16_to_cpu(false, vnet_hdr.csum_offset) + 2 >
> - __virtio16_to_cpu(false, vnet_hdr.hdr_len)))
> - vnet_hdr.hdr_len = __cpu_to_virtio16(false,
> - __virtio16_to_cpu(false, vnet_hdr.csum_start) +
> - __virtio16_to_cpu(false, vnet_hdr.csum_offset) + 2);
> + (__virtio16_to_cpu(vio_le(), vnet_hdr.csum_start) +
> + __virtio16_to_cpu(vio_le(), vnet_hdr.csum_offset) + 2 >
> + __virtio16_to_cpu(vio_le(), vnet_hdr.hdr_len)))
> + vnet_hdr.hdr_len = __cpu_to_virtio16(vio_le(),
> + __virtio16_to_cpu(vio_le(), vnet_hdr.csum_start) +
> + __virtio16_to_cpu(vio_le(), vnet_hdr.csum_offset) + 2);
>
> err = -EINVAL;
> - if (__virtio16_to_cpu(false, vnet_hdr.hdr_len) > len)
> + if (__virtio16_to_cpu(vio_le(), vnet_hdr.hdr_len) > len)
> goto out_unlock;
>
> if (vnet_hdr.gso_type != VIRTIO_NET_HDR_GSO_NONE) {
> @@ -2731,7 +2733,7 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)
> hlen = LL_RESERVED_SPACE(dev);
> tlen = dev->needed_tailroom;
> skb = packet_alloc_skb(sk, hlen + tlen, hlen, len,
> - __virtio16_to_cpu(false, vnet_hdr.hdr_len),
> + __virtio16_to_cpu(vio_le(), vnet_hdr.hdr_len),
> msg->msg_flags & MSG_DONTWAIT, &err);
> if (skb == NULL)
> goto out_unlock;
> @@ -2778,8 +2780,8 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)
>
> if (po->has_vnet_hdr) {
> if (vnet_hdr.flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) {
> - u16 s = __virtio16_to_cpu(false, vnet_hdr.csum_start);
> - u16 o = __virtio16_to_cpu(false, vnet_hdr.csum_offset);
> + u16 s = __virtio16_to_cpu(vio_le(), vnet_hdr.csum_start);
> + u16 o = __virtio16_to_cpu(vio_le(), vnet_hdr.csum_offset);
> if (!skb_partial_csum_set(skb, s, o)) {
> err = -EINVAL;
> goto out_free;
> @@ -2787,7 +2789,7 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)
> }
>
> skb_shinfo(skb)->gso_size =
> - __virtio16_to_cpu(false, vnet_hdr.gso_size);
> + __virtio16_to_cpu(vio_le(), vnet_hdr.gso_size);
> skb_shinfo(skb)->gso_type = gso_type;
>
> /* Header must be checked, and gso_segs computed. */
> @@ -3161,9 +3163,9 @@ static int packet_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
>
> /* This is a hint as to how much should be linear. */
> vnet_hdr.hdr_len =
> - __cpu_to_virtio16(false, skb_headlen(skb));
> + __cpu_to_virtio16(vio_le(), skb_headlen(skb));
> vnet_hdr.gso_size =
> - __cpu_to_virtio16(false, sinfo->gso_size);
> + __cpu_to_virtio16(vio_le(), sinfo->gso_size);
> if (sinfo->gso_type & SKB_GSO_TCPV4)
> vnet_hdr.gso_type = VIRTIO_NET_HDR_GSO_TCPV4;
> else if (sinfo->gso_type & SKB_GSO_TCPV6)
> @@ -3181,9 +3183,9 @@ static int packet_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
>
> if (skb->ip_summed == CHECKSUM_PARTIAL) {
> vnet_hdr.flags = VIRTIO_NET_HDR_F_NEEDS_CSUM;
> - vnet_hdr.csum_start = __cpu_to_virtio16(false,
> + vnet_hdr.csum_start = __cpu_to_virtio16(vio_le(),
> skb_checksum_start_offset(skb));
> - vnet_hdr.csum_offset = __cpu_to_virtio16(false,
> + vnet_hdr.csum_offset = __cpu_to_virtio16(vio_le(),
> skb->csum_offset);
> } else if (skb->ip_summed == CHECKSUM_UNNECESSARY) {
> vnet_hdr.flags = VIRTIO_NET_HDR_F_DATA_VALID;
>
--
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