Virtio vring send and receive queue creation process

For the question of the review document that day, and looked at the code, the Virtio send and receive queue is created in the guest's front-end driver

Guest front-end driver, take network devices as an example: After VIRTIO-NET:PCI discovery, the transceiver queue is allocated via the PCI bus

static int virtnet_probe (Structvirtio_device *vdev)

{

......

/*

* Initialize Virtqueue

* Create and initialize Send/Receive queues

*/

Err = Init_vqs (vi);

......

}

/* Create and initialize send/Receive queues */

static int Init_vqs (struct virtnet_info*vi)

{

/* Assign */

ret = Virtnet_alloc_queues (vi);

if (ret)

Goto err;

/* Create vring*/with Find Vqs

ret = Virtnet_find_vqs (vi);

if (ret)

Goto Err_free;

......

}

/* Create vring*/with Find Vqs

static int Virtnet_find_vqs (Structvirtnet_info *vi)

{

......

/* Call is Vp_find_vqs, really create the VIRTQUEUE internal structure and assign the address, and tell the address to the backend QEMU driver */

ret = Vi->vdev->config->find_vqs (Vi->vdev,total_vqs, Vqs, callbacks, names);

......

}

VIRTIO PCI bus

static int Vp_find_vqs (struct virtio_device*vdev, unsigned NVQs,

struct Virtqueue *vqs[],

vq_callback_t *callbacks[],

const CHAR *names[])

{

int err;

Err = Vp_try_to_find_vqs (Vdev,nvqs, Vqs, callbacks, names, true, true);

Err = Vp_try_to_find_vqs (Vdev,nvqs, Vqs, callbacks, names, true, false);

Return Vp_try_to_find_vqs (Vdev,nvqs, Vqs, callbacks, names, false, false);

}

static int Vp_try_to_find_vqs ()

{

......

/* The core is SETUP_VQ () */

Vqs[i] = SETUP_VQ (Vdev,i, Callbacks[i], names[i], Msix_vec);

......

}

static struct Virtqueue *setup_vq (structvirtio_device *vdev, unsigned index,

void (*callback) (struct virtqueue *vq),

const Char *name,

U16 Msix_vec)

{

/* Set the address of the Virtio vring to the backend qemu*/

Iowrite32 (Virt_to_phys (info->queue) >> virtio_pci_queue_addr_shift, Vp_dev->ioaddr +virtio_pci_queue_ PFN);

}

 

IO read/write is intercepted by backend QEMU for simulation

Qemu back-end driver

static void Virtio_ioport_write (Void*opaque, uint32_t addr, uint32_t val)

{

......

Switch (addr) {

Case VIRTIO_PCI_QUEUE_PFN:

PA = (hwaddr) val << virtio_pci_queue_addr_shift;

......

Virtio_queue_set_addr (Vdev,vdev->queue_sel, PA);

......

}

There is also a detail problem, the front-end driver writes should be qeueu GPA "IOWRITE32 (Virt_to_phys (info->queue) >> virtio_pci_queue_addr_shift,vp_dev- >IOADDR + VIRTIO_PCI_QUEUE_PFN); "

This was intercepted by the backend qemu, how does QEMU directly use GPA? Where to complete the conversion of Gpa->hva?

This is the conversion when QEMU takes the message from the Virtqueue.

QEMU code, after receiving the Virtio notification, the message is removed from the Shared queue via Virtqueue_pop

Intvirtqueue_pop (Virtqueue *vq, virtqueueelement *elem)

{

/*now Map What do we have collected */

Virtqueue_map_sg (Elem->in_sg,elem->in_addr, Elem->in_num, 1);

Virtqueue_map_sg (elem->out_sg,elem->out_addr, elem->out_num, 0);

}

Voidvirtqueue_map_sg ()

{

for (i = 0; i < Num_sg; i++) {

len = Sg[i].iov_len;

Sg[i].iov_base =cpu_physical_memory_map (Addr[i], &len, is_write);

if (sg[i].iov_base = = NULL | | Len! = sg[i].iov_len) {

Error_report ("Virtio:trying to map MMIO memory");

Exit (1);

}

}

}

/* Complete a guest's physical address conversion from GPA to HVA */

Void*cpu_physical_memory_map (hwaddr addr,

Hwaddr *plen,

int is_write)

{

Return Address_space_map (&address_space_memory,addr, Plen, is_write);

}

Thanks

Feng

Virtio Official spec in

Http://docs.oasis-open.org/virtio/virtio/v1.0/virtio-v1.0.html