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SubjectRe: [PATCH 2/5] /dev/vring: simple userspace-kernel ringbuffer interface.
Hi.

On Fri, Apr 18, 2008 at 02:39:48PM +1000, Rusty Russell (rusty@rustcorp.com.au) wrote:

> +int vring_get_buffer(struct vring_info *vr,
> + struct iovec *in_iov,
> + unsigned int *num_in, unsigned long *in_len,
> + struct iovec *out_iov,
> + unsigned int *num_out, unsigned long *out_len)
> +{
> + unsigned int i, in = 0, out = 0;
> + unsigned long dummy;
> + u16 avail, last_avail, head;
> + struct vring_desc d;

Should this whole function and vring_used_buffer() be protected with
vr->lock mutex?

> + if (unlikely(get_user(avail, &vr->ring.avail->idx)))
> + return -EFAULT;
> + if (unlikely(get_user(last_avail, &vring_last_avail(&vr->ring))))
> + return -EFAULT;
> +
> + if (last_avail == avail)
> + return 0;
> +
> + if (!in_len)
> + in_len = &dummy;
> + if (!out_len)
> + out_len = &dummy;
> +
> + *in_len = *out_len = 0;
> +
> + if (unlikely(get_user(head, &vr->ring.avail->ring[last_avail
> + & vr->mask])))
> + return -EFAULT;
> +
> + i = head;
> + do {
> + if (unlikely(i >= vr->ring.num)) {
> + pr_debug("vring: bad index: %u\n", i);
> + return -EINVAL;
> + }
> +
> + if (copy_from_user(&d, &vr->ring.desc[i], sizeof(d)) != 0)
> + return -EFAULT;
> +
> + if (d.flags & VRING_DESC_F_WRITE) {
> + /* Check for length and iovec overflows */
> + if (!num_in) {
> + pr_debug("vring: writable desc %u in ring %p\n",
> + i, vr->ring.desc);
> + return -EINVAL;
> + }
> + if (in == *num_in || *in_len + d.len < *in_len)
> + return -E2BIG;
> + in_iov[in].iov_len = d.len;
> + *in_len += d.len;
> + in_iov[in].iov_base = (void __user *)(long)d.addr;
> + in++;
> + } else {
> + if (!num_out) {
> + pr_debug("vring: readable desc %u in ring %p\n",
> + i, vr->ring.desc);
> + return -EINVAL;
> + }
> + if (out == *num_out || *out_len + d.len < *out_len)
> + return -E2BIG;
> + out_iov[out].iov_len = d.len;
> + *out_len += d.len;
> + out_iov[out].iov_base = (void __user *)(long)d.addr;
> + out++;
> + }
> +
> + i = d.next;
> + } while (d.flags & VRING_DESC_F_NEXT);
> +
> + if (num_in)
> + *num_in = in;
> + if (num_out)
> + *num_out = out;
> +
> + last_avail++;
> + put_user(last_avail, &vring_last_avail(&vr->ring));
> +
> + /* 0 is a valid head, so add one. */
> + return head + 1;
> +}
> +EXPORT_SYMBOL_GPL(vring_get_buffer);
> +
> +/**
> + * vring_used_buffer - return a used buffer to the vring
> + * @vr: the vring
> + * @id: the id returned from vring_get_buffer
> + * @len: the total bytes *written* to the buffer
> + */
> +void vring_used_buffer(struct vring_info *vr, int id, u32 len)
> +{
> + struct vring_used_elem used;
> + u16 used_idx;
> +
> + BUG_ON(id <= 0 || id > vr->ring.num);
> +
> + used.id = id - 1;
> + used.len = len;
> + if (get_user(used_idx, &vr->ring.used->idx) != 0)
> + return;
> +
> + if (copy_to_user(&vr->ring.used->ring[used_idx & vr->mask], &used,
> + sizeof(used)))
> + return;
> +
> + wmb();
> + used_idx++;
> + put_user(used_idx, &vr->ring.used->idx);
> +}
> +EXPORT_SYMBOL_GPL(vring_used_buffer);

--
Evgeniy Polyakov


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