Re: [Qemu-devel] [PATCH v4 07/11] libqos: Added basic virtqueue support to virtio implementation

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Tue, Aug 12, 2014 at 01:41:52PM +0200, Marc Marí wrote:
> +    /* Check power of 2 */
> +    aux = vq->size;
> +    while ((aux & 1) != 0) {
> +        aux = aux >> 1;
> +    }
> +    g_assert_cmpint(aux, !=, 1);

Power of 2 can be tested like this without a while loop:
g_assert_cmpint(vq->size & (vq->size - 1), ==, 0)

> +void qvring_init(const QGuestAllocator *alloc, QVirtQueue *vq, uint64_t addr)
> +{
> +    int i;
> +
> +    vq->desc = addr;
> +    vq->avail = vq->desc + vq->size*sizeof(QVRingDesc);
> +    vq->used = (uint64_t)((vq->avail + sizeof(uint16_t) * (3 + vq->size)
> +        +vq->align-1) & ~(vq->align - 1));
> +
> +    for (i = 0; i < vq->size-1; i++) {
> +        /* vq->desc[i].addr */
> +        writew(vq->desc+(16*i), 0);
> +        /* vq->desc[i].next */
> +        writew(vq->desc+(16*i)+14, i+1);
> +    }

Please use space between operators:
writew(vq->desc + (16 * i) + 14, i + 1)

This applies to all patches.

> +void qvirtqueue_kick(const QVirtioBus *bus, QVirtioDevice *d, QVirtQueue *vq,
> +                                                            uint32_t free_head)
> +{
> +    /* vq->avail->idx */
> +    uint16_t idx = readl(vq->avail+2);
> +
> +    /* vq->avail->ring[idx % vq->size] */
> +    writel(vq->avail+4+(2*(idx % vq->size)), free_head);

If you want to use typed pointers you can.  It will make the code nicer
to read, just be careful never to dereference them and only to access
through writel()/readl():

typedef struct {
uint16_t foo; /* Forgot what these fields are called and didn't check */
uint16_t bar;
uint16_t ring[];
} VirtioAvail;

writel(&vq->avail.ring[idx % vq->size], free_head);

Now it looks more like normal C and the compiler is doing the address
calculations for us.

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