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Date: Sun, 7 Mar 2010 18:12:29 +0200
From: "Michael S. Tsirkin" <mst@...hat.com>
To: David Stevens <dlstevens@...ibm.com>
Cc: rusty@...tcorp.com.au, netdev@...r.kernel.org, kvm@...r.kernel.org,
virtualization@...ts.osdl.org
Subject: Re: [RFC][ PATCH 2/3] vhost-net: handle vnet_hdr processing for
MRG_RX_BUF
On Tue, Mar 02, 2010 at 05:20:26PM -0700, David Stevens wrote:
> This patch adds vnet_hdr processing for mergeable buffer
> support to vhost-net.
>
> Signed-off-by: David L Stevens <dlstevens@...ibm.com>
>
> diff -ruN net-next-p1/drivers/vhost/net.c net-next-p2/drivers/vhost/net.c
Could you please add -p to diff flags so that it's easier
to figure out which function is changes?
> --- net-next-p1/drivers/vhost/net.c 2010-03-01 11:44:22.000000000
> -0800
> +++ net-next-p2/drivers/vhost/net.c 2010-03-02 13:01:34.000000000
> -0800
> @@ -109,7 +109,6 @@
> };
> size_t len, total_len = 0;
> int err, wmem;
> - size_t hdr_size;
> struct socket *sock = rcu_dereference(vq->private_data);
> if (!sock)
> return;
> @@ -124,7 +123,6 @@
>
> if (wmem < sock->sk->sk_sndbuf * 2)
> tx_poll_stop(net);
> - hdr_size = vq->hdr_size;
>
> for (;;) {
> head.iov_base = (void *)vhost_get_vq_desc(&net->dev, vq,
> @@ -148,25 +146,45 @@
> "out %d, int %d\n", out, in);
> break;
> }
> + if (vq->guest_hlen > vq->sock_hlen) {
> + if (msg.msg_iov[0].iov_len == vq->guest_hlen)
> + msg.msg_iov[0].iov_len = vq->sock_hlen;
> + else if (out == ARRAY_SIZE(vq->iov))
> + vq_err(vq, "handle_tx iov overflow!");
> + else {
> + int i;
> +
> + /* give header its own iov */
> + for (i=out; i>0; ++i)
> + msg.msg_iov[i+1] = msg.msg_iov[i];
> + msg.msg_iov[0].iov_len = vq->sock_hlen;
> + msg.msg_iov[1].iov_base += vq->guest_hlen;
> + msg.msg_iov[1].iov_len -= vq->guest_hlen;
> + out++;
We seem to spend a fair bit of code here and elsewhere trying to cover
the diff between header size in guest and host. In hindsight, it was
not a good idea to put new padding between data and the header:
virtio-net should have added it *before*. But it is what it is.
Wouldn't it be easier to just add an ioctl to tap so that
vnet header size is made bigger by 4 bytes?
> + }
> + }
> /* Skip header. TODO: support TSO. */
> - s = move_iovec_hdr(vq->iov, vq->hdr, hdr_size, out);
> msg.msg_iovlen = out;
> head.iov_len = len = iov_length(vq->iov, out);
> /* Sanity check */
> if (!len) {
> vq_err(vq, "Unexpected header len for TX: "
> "%zd expected %zd\n",
> - iov_length(vq->hdr, s), hdr_size);
> + len, vq->guest_hlen);
> break;
> }
> /* TODO: Check specific error and bomb out unless ENOBUFS?
> */
> err = sock->ops->sendmsg(NULL, sock, &msg, len);
> if (unlikely(err < 0)) {
> - vhost_discard(vq, 1);
> - tx_poll_start(net, sock);
> + if (err == -EAGAIN) {
The comment mentions ENOBUFS. Are you sure it's EAGAIN?
> + tx_poll_start(net, sock);
Don't we need to call discard to move the last avail header back?
> + } else {
> + vq_err(vq, "sendmsg: errno %d\n", -err);
> + /* drop packet; do not discard/resend */
> + vhost_add_used_and_signal(&net->dev,vq,&head,1);
> + }
> break;
> - }
> - if (err != len)
> + } else if (err != len)
Previous if ends with break so no need for else here.
> pr_err("Truncated TX packet: "
> " len %d != %zd\n", err, len);
> vhost_add_used_and_signal(&net->dev, vq, &head, 1);
> @@ -207,14 +225,8 @@
> .msg_flags = MSG_DONTWAIT,
> };
>
> - struct virtio_net_hdr hdr = {
> - .flags = 0,
> - .gso_type = VIRTIO_NET_HDR_GSO_NONE
> - };
> -
> size_t len, total_len = 0;
> int err, headcount, datalen;
> - size_t hdr_size;
> struct socket *sock = rcu_dereference(vq->private_data);
>
> if (!sock || !skb_head_len(&sock->sk->sk_receive_queue))
> @@ -223,7 +235,6 @@
> use_mm(net->dev.mm);
> mutex_lock(&vq->mutex);
> vhost_disable_notify(vq);
> - hdr_size = vq->hdr_size;
>
> vq_log = unlikely(vhost_has_feature(&net->dev, VHOST_F_LOG_ALL)) ?
> vq->log : NULL;
> @@ -232,25 +243,18 @@
> headcount = vhost_get_heads(vq, datalen, &in, vq_log,
> &log);
> /* OK, now we need to know about added descriptors. */
> if (!headcount) {
> - if (unlikely(vhost_enable_notify(vq))) {
> - /* They have slipped one in as we were
> - * doing that: check again. */
> - vhost_disable_notify(vq);
> - continue;
> - }
> - /* Nothing new? Wait for eventfd to tell us
> - * they refilled. */
> + vhost_enable_notify(vq);
You don't think this race can happen?
> break;
> }
> /* Skip header. TODO: support TSO/mergeable rx buffers. */
> - s = move_iovec_hdr(vq->iov, vq->hdr, hdr_size, in);
> msg.msg_iovlen = in;
> len = iov_length(vq->iov, in);
> +
> /* Sanity check */
> if (!len) {
> vq_err(vq, "Unexpected header len for RX: "
> "%zd expected %zd\n",
> - iov_length(vq->hdr, s), hdr_size);
> + len, vq->guest_hlen);
> break;
> }
> err = sock->ops->recvmsg(NULL, sock, &msg,
> @@ -268,13 +272,7 @@
> continue;
> }
> len = err;
> - err = memcpy_toiovec(vq->hdr, (unsigned char *)&hdr,
> hdr_size);
> - if (err) {
> - vq_err(vq, "Unable to write vnet_hdr at addr %p:
> %d\n",
> - vq->iov->iov_base, err);
> - break;
> - }
> - len += hdr_size;
> + len += vq->guest_hlen - vq->sock_hlen;
> vhost_add_used_and_signal(&net->dev, vq, vq->heads,
> headcount);
> if (unlikely(vq_log))
> vhost_log_write(vq, vq_log, log, len);
> @@ -483,6 +481,13 @@
> return ERR_PTR(-ENOTSOCK);
> }
>
> +static int vhost_sock_is_raw(struct socket *sock)
> +{
> + if (!sock || !sock->sk)
> + return 0;
> + return sock->sk->sk_type == SOCK_RAW;
> +}
> +
> static long vhost_net_set_backend(struct vhost_net *n, unsigned index,
> int fd)
> {
> struct socket *sock, *oldsock;
> @@ -519,6 +524,20 @@
>
> vhost_net_disable_vq(n, vq);
> rcu_assign_pointer(vq->private_data, sock);
> +
> + if (sock && sock->sk) {
> + if (!vhost_sock_is_raw(sock) ||
I dislike this backend-specific code, it ties us with specifics of
backend implementations, which change without notice. Ideally all
backend-specific stuff should live in userspace, userspace programs
vhost device appropriately.
> + vhost_has_feature(&n->dev,
> VHOST_NET_F_VIRTIO_NET_HDR)) {
> + vq->sock_hlen = sizeof(struct virtio_net_hdr);
> + if (vhost_has_feature(&n->dev,
> VIRTIO_NET_F_MRG_RXBUF))
> + vq->guest_hlen =
> + sizeof(struct
> virtio_net_hdr_mrg_rxbuf);
> + else
> + vq->guest_hlen = sizeof(struct
> virtio_net_hdr);
> + } else
> + vq->guest_hlen = vq->sock_hlen = 0;
> + } else
> + vq_err(vq, "vhost_net_set_backend: sock->sk is NULL");
As proposed above, IMO it would be nicer to add an ioctl in tap
that let us program header size.
> vhost_net_enable_vq(n, vq);
> mutex_unlock(&vq->mutex);
> done:
> @@ -566,8 +585,17 @@
> n->dev.acked_features = features;
> smp_wmb();
> for (i = 0; i < VHOST_NET_VQ_MAX; ++i) {
> - mutex_lock(&n->vqs[i].mutex);
> - n->vqs[i].hdr_size = hdr_size;
> + struct vhost_virtqueue *vq = n->vqs + i;
> + struct socket *sock = vq->private_data;
> +
> + mutex_lock(&vq->mutex);
> + if (features & (1 << VIRTIO_NET_F_MRG_RXBUF))
> + vq->sock_hlen = sizeof(struct
> virtio_net_hdr_mrg_rxbuf);
> + else if (features & (1 << VHOST_NET_F_VIRTIO_NET_HDR) ||
> + !vhost_sock_is_raw(sock))
> + vq->sock_hlen = sizeof(struct virtio_net_hdr);
> + else
> + vq->sock_hlen = 0;
> mutex_unlock(&n->vqs[i].mutex);
> }
> vhost_net_flush(n);
> diff -ruN net-next-p1/drivers/vhost/vhost.c
> net-next-p2/drivers/vhost/vhost.c
> --- net-next-p1/drivers/vhost/vhost.c 2010-03-01 11:44:06.000000000
> -0800
> +++ net-next-p2/drivers/vhost/vhost.c 2010-03-02 12:53:02.000000000
> -0800
> @@ -113,7 +113,8 @@
> vq->used_flags = 0;
> vq->log_used = false;
> vq->log_addr = -1ull;
> - vq->hdr_size = 0;
> + vq->guest_hlen = 0;
> + vq->sock_hlen = 0;
> vq->private_data = NULL;
> vq->log_base = NULL;
> vq->error_ctx = NULL;
> @@ -848,20 +849,85 @@
> return 0;
> }
>
> +static int
> +vhost_get_hdr(struct vhost_virtqueue *vq, int *in, struct vhost_log *log,
> + int *log_num)
> +{
> + struct iovec *heads = vq->heads;
> + struct iovec *iov = vq->iov;
> + int out;
> +
> + *in = 0;
> + iov[0].iov_len = 0;
> +
> + /* get buffer, starting from iov[1] */
> + heads[0].iov_base = (void *)vhost_get_vq_desc(vq->dev, vq,
> + vq->iov+1, ARRAY_SIZE(vq->iov)-1, &out, in, log, log_num);
> + if (out || *in <= 0) {
> + vq_err(vq, "unexpected descriptor format for RX: out %d, "
> + "in %d\n", out, *in);
> + return 0;
> + }
> + if (heads[0].iov_base == (void *)vq->num)
> + return 0;
> +
> + /* make iov[0] the header */
> + if (!vq->guest_hlen) {
> + if (vq->sock_hlen) {
> + static struct virtio_net_hdr junk; /* bit bucket
> */
> +
> + iov[0].iov_base = &junk;
> + iov[0].iov_len = sizeof(junk);
> + } else
> + iov[0].iov_len = 0;
> + }
> + if (vq->sock_hlen < vq->guest_hlen) {
> + iov[0].iov_base = iov[1].iov_base;
> + iov[0].iov_len = vq->sock_hlen;
> +
> + if (iov[1].iov_len < vq->sock_hlen) {
> + vq_err(vq, "can't fit header in one buffer!");
> + vhost_discard(vq, 1);
> + return 0;
> + }
> + if (!vq->sock_hlen) {
> + static const struct virtio_net_hdr_mrg_rxbuf hdr =
> {
> + .hdr.flags = 0,
> + .hdr.gso_type = VIRTIO_NET_HDR_GSO_NONE
> + };
> + memcpy(iov[0].iov_base, &hdr, vq->guest_hlen);
> + }
> + iov[1].iov_base += vq->guest_hlen;
> + iov[1].iov_len -= vq->guest_hlen;
> + }
> + return 1;
The above looks kind of scary, lots of special-casing. I'll send a
patch for tap to set vnet header size, let's see if it makes life easier
for us.
> +}
> +
> unsigned vhost_get_heads(struct vhost_virtqueue *vq, int datalen, int
> *iovcount,
> struct vhost_log *log, unsigned int *log_num)
> {
> struct iovec *heads = vq->heads;
> - int out, in;
> + int out, in = 0;
> + int seg = 0;
> int hc = 0;
I think it's better to stick to simple names like i
for index variables, alternatively give it a meaningful
name like "count".
>
> + if (vq->guest_hlen != vq->sock_hlen) {
Sticking guest_hlen/sock_hlen in vhost is somewhat ugly.
> + seg = vhost_get_hdr(vq, &in, log, log_num);
> + if (!seg)
> + return 0;
> + hc++;
> + datalen -= iov_length(vq->iov+seg, in);
> + seg += in;
> + }
> +
> while (datalen > 0) {
> if (hc >= VHOST_NET_MAX_SG) {
> vhost_discard(vq, hc);
> return 0;
> }
> heads[hc].iov_base = (void *)vhost_get_vq_desc(vq->dev,
> vq,
> - vq->iov, ARRAY_SIZE(vq->iov), &out, &in, log,
> log_num);
> + vq->iov+seg, ARRAY_SIZE(vq->iov)-seg, &out, &in,
> + log, log_num);
> if (heads[hc].iov_base == (void *)vq->num) {
> vhost_discard(vq, hc);
> return 0;
> @@ -872,11 +938,12 @@
> vhost_discard(vq, hc);
> return 0;
> }
> - heads[hc].iov_len = iov_length(vq->iov, in);
> - hc++;
> + heads[hc].iov_len = iov_length(vq->iov+seg, in);
> datalen -= heads[hc].iov_len;
> + hc++;
> + seg += in;
> }
> - *iovcount = in;
> + *iovcount = seg;
> return hc;
> }
>
> diff -ruN net-next-p1/drivers/vhost/vhost.h
> net-next-p2/drivers/vhost/vhost.h
> --- net-next-p1/drivers/vhost/vhost.h 2010-03-01 11:42:18.000000000
> -0800
> +++ net-next-p2/drivers/vhost/vhost.h 2010-03-02 13:02:03.000000000
> -0800
> @@ -82,10 +82,9 @@
> u64 log_addr;
>
> struct iovec indirect[VHOST_NET_MAX_SG];
> - struct iovec iov[VHOST_NET_MAX_SG];
> - struct iovec hdr[VHOST_NET_MAX_SG];
> + struct iovec iov[VHOST_NET_MAX_SG+1]; /* an extra for vnet hdr */
> struct iovec heads[VHOST_NET_MAX_SG];
> - size_t hdr_size;
> + size_t guest_hlen, sock_hlen;
> /* We use a kind of RCU to access private pointer.
> * All readers access it from workqueue, which makes it possible
> to
> * flush the workqueue instead of synchronize_rcu. Therefore
> readers do
>
--
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