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Date: Mon, 10 Aug 2009 21:51:18 +0200
From: Arnd Bergmann <arnd@...db.de>
To: virtualization@...ts.linux-foundation.org
Cc: "Michael S. Tsirkin" <mst@...hat.com>, netdev@...r.kernel.org,
kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] vhost_net: a kernel-level virtio server
On Monday 10 August 2009, Michael S. Tsirkin wrote:
> What it is: vhost net is a character device that can be used to reduce
> the number of system calls involved in virtio networking.
> Existing virtio net code is used in the guest without modification.
Very nice, I loved reading it. It's getting rather late in my time
zone, so this comments only on the network driver. I'll go through
the rest tomorrow.
> @@ -293,6 +293,7 @@ static int __devinit virtblk_probe(struct virtio_device *vdev)
> err = PTR_ERR(vblk->vq);
> goto out_free_vblk;
> }
> + printk(KERN_ERR "vblk->vq = %p\n", vblk->vq);
>
> vblk->pool = mempool_create_kmalloc_pool(1,sizeof(struct virtblk_req));
> if (!vblk->pool) {
> @@ -383,6 +384,8 @@ static int __devinit virtblk_probe(struct virtio_device *vdev)
> if (!err)
> blk_queue_logical_block_size(vblk->disk->queue, blk_size);
>
> + printk(KERN_ERR "virtio_config_val returned %d\n", err);
> +
> add_disk(vblk->disk);
> return 0;
I guess you meant to remove these before submitting.
> +static void handle_tx_kick(struct work_struct *work);
> +static void handle_rx_kick(struct work_struct *work);
> +static void handle_tx_net(struct work_struct *work);
> +static void handle_rx_net(struct work_struct *work);
[style] I think the code gets more readable if you reorder it
so that you don't need forward declarations for static functions.
> +static long vhost_net_reset_owner(struct vhost_net *n)
> +{
> + struct socket *sock = NULL;
> + long r;
> + mutex_lock(&n->dev.mutex);
> + r = vhost_dev_check_owner(&n->dev);
> + if (r)
> + goto done;
> + sock = vhost_net_stop(n);
> + r = vhost_dev_reset_owner(&n->dev);
> +done:
> + mutex_unlock(&n->dev.mutex);
> + if (sock)
> + fput(sock->file);
> + return r;
> +}
what is the difference between vhost_net_reset_owner(n)
and vhost_net_set_socket(n, -1)?
> +
> +static struct file_operations vhost_net_fops = {
> + .owner = THIS_MODULE,
> + .release = vhost_net_release,
> + .unlocked_ioctl = vhost_net_ioctl,
> + .open = vhost_net_open,
> +};
This is missing a compat_ioctl pointer. It should simply be
static long vhost_net_compat_ioctl(struct file *f,
unsigned int ioctl, unsigned long arg)
{
return f, ioctl, (unsigned long)compat_ptr(arg);
}
> +/* Bits from fs/aio.c. TODO: export and use from there? */
> +/*
> + * use_mm
> + * Makes the calling kernel thread take on the specified
> + * mm context.
> + * Called by the retry thread execute retries within the
> + * iocb issuer's mm context, so that copy_from/to_user
> + * operations work seamlessly for aio.
> + * (Note: this routine is intended to be called only
> + * from a kernel thread context)
> + */
> +static void use_mm(struct mm_struct *mm)
> +{
> + struct mm_struct *active_mm;
> + struct task_struct *tsk = current;
> +
> + task_lock(tsk);
> + active_mm = tsk->active_mm;
> + atomic_inc(&mm->mm_count);
> + tsk->mm = mm;
> + tsk->active_mm = mm;
> + switch_mm(active_mm, mm, tsk);
> + task_unlock(tsk);
> +
> + mmdrop(active_mm);
> +}
Why do you need a kernel thread here? If the data transfer functions
all get called from a guest intercept, shouldn't you already be
in the right mm?
> +static void handle_tx(struct vhost_net *net)
> +{
> + struct vhost_virtqueue *vq = &net->dev.vqs[VHOST_NET_VQ_TX];
> + unsigned head, out, in;
> + struct msghdr msg = {
> + .msg_name = NULL,
> + .msg_namelen = 0,
> + .msg_control = NULL,
> + .msg_controllen = 0,
> + .msg_iov = (struct iovec *)vq->iov + 1,
> + .msg_flags = MSG_DONTWAIT,
> + };
> + size_t len;
> + int err;
> + struct socket *sock = rcu_dereference(net->sock);
> + if (!sock || !sock_writeable(sock->sk))
> + return;
> +
> + use_mm(net->dev.mm);
> + mutex_lock(&vq->mutex);
> + for (;;) {
> + head = vhost_get_vq_desc(&net->dev, vq, vq->iov, &out, &in);
> + if (head == vq->num)
> + break;
> + if (out <= 1 || in) {
> + vq_err(vq, "Unexpected descriptor format for TX: "
> + "out %d, int %d\n", out, in);
> + break;
> + }
> + /* Sanity check */
> + if (vq->iov->iov_len != sizeof(struct virtio_net_hdr)) {
> + vq_err(vq, "Unexpected header len for TX: "
> + "%ld expected %zd\n", vq->iov->iov_len,
> + sizeof(struct virtio_net_hdr));
> + break;
> + }
> + /* Skip header. TODO: support TSO. */
> + msg.msg_iovlen = out - 1;
> + len = iov_length(vq->iov + 1, out - 1);
> + /* TODO: Check specific error and bomb out unless ENOBUFS? */
> + err = sock->ops->sendmsg(NULL, sock, &msg, len);
> + if (err < 0) {
> + vhost_discard_vq_desc(vq);
> + break;
> + }
> + if (err != len)
> + pr_err("Truncated TX packet: "
> + " len %d != %zd\n", err, len);
> + vhost_add_used_and_trigger(vq, head,
> + len + sizeof(struct virtio_net_hdr));
> + }
> +
> + mutex_unlock(&vq->mutex);
> + unuse_mm(net->dev.mm);
> +}
I guess that this is where one could plug into macvlan directly, using
sock_alloc_send_skb/memcpy_fromiovec/dev_queue_xmit directly,
instead of filling a msghdr for each, if we want to combine this
with the work I did on that.
Arnd <><
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