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SubjectRe: [PATCH 07/17] new helpers: skb_copy_datagram_from_iter() and zerocopy_sg_from_iter()
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On Sat, 2014-11-22 at 04:33 +0000, Al Viro wrote:
[...]
> --- a/net/core/datagram.c
> +++ b/net/core/datagram.c
> @@ -572,6 +572,77 @@ fault:
> }
> EXPORT_SYMBOL(skb_copy_datagram_from_iovec);
>

Missing kernel-doc.

> +int skb_copy_datagram_from_iter(struct sk_buff *skb, int offset,
> + struct iov_iter *from,
> + int len)
> +{
> + int start = skb_headlen(skb);
> + int i, copy = start - offset;
> + struct sk_buff *frag_iter;
> +
> + /* Copy header. */
> + if (copy > 0) {
> + if (copy > len)
> + copy = len;
> + if (copy_from_iter(skb->data + offset, copy, from) != copy)
> + goto fault;
> + if ((len -= copy) == 0)
> + return 0;
> + offset += copy;
> + }
> +
> + /* Copy paged appendix. Hmm... why does this look so complicated? */
> + for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
> + int end;
> + const skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
> +
> + WARN_ON(start > offset + len);
> +
> + end = start + skb_frag_size(frag);
> + if ((copy = end - offset) > 0) {
> + size_t copied;

Blank line needed after a declaration.

> + if (copy > len)
> + copy = len;
> + copied = copy_page_from_iter(skb_frag_page(frag),
> + frag->page_offset + offset - start,
> + copy, from);
> + if (copied != copy)
> + goto fault;
> +
> + if (!(len -= copy))
> + return 0;

The other two instances of this condition are written as:

if ((len -= copy) == 0)
Similarly in skb_copy_bits().

> + offset += copy;
> + }
> + start = end;
> + }
> +
> + skb_walk_frags(skb, frag_iter) {
> + int end;
> +
> + WARN_ON(start > offset + len);
> +
> + end = start + frag_iter->len;
> + if ((copy = end - offset) > 0) {
> + if (copy > len)
> + copy = len;
> + if (skb_copy_datagram_from_iter(frag_iter,
> + offset - start,
> + from, copy))
> + goto fault;
> + if ((len -= copy) == 0)
> + return 0;
> + offset += copy;
> + }
> + start = end;
> + }
> + if (!len)
> + return 0;
> +
> +fault:
> + return -EFAULT;
> +}
> +EXPORT_SYMBOL(skb_copy_datagram_from_iter);
> +
> /**
> * zerocopy_sg_from_iovec - Build a zerocopy datagram from an iovec
> * @skb: buffer to copy
> @@ -643,6 +714,50 @@ int zerocopy_sg_from_iovec(struct sk_buff *skb, const struct iovec *from,
> }
> EXPORT_SYMBOL(zerocopy_sg_from_iovec);
>

Missing kernel-doc.

> +int zerocopy_sg_from_iter(struct sk_buff *skb, struct iov_iter *from)
> +{
> + int len = iov_iter_count(from);
> + int copy = min_t(int, skb_headlen(skb), len);
> + int i = 0;
> +
> + /* copy up to skb headlen */
> + if (skb_copy_datagram_from_iter(skb, 0, from, copy))
> + return -EFAULT;
> +
> + while (iov_iter_count(from)) {
> + struct page *pages[MAX_SKB_FRAGS];
> + size_t start;
> + ssize_t copied;
> + unsigned long truesize;
> + int n = 0;
> +
> + copied = iov_iter_get_pages(from, pages, ~0U, MAX_SKB_FRAGS, &start);
> + if (copied < 0)
> + return -EFAULT;
> +
> + truesize = DIV_ROUND_UP(copied + start, PAGE_SIZE) * PAGE_SIZE;

PAGE_ALIGN(copied + start) ?

> + skb->data_len += copied;
> + skb->len += copied;
> + skb->truesize += truesize;
> + atomic_add(truesize, &skb->sk->sk_wmem_alloc);
> + while (copied) {
> + int off = start;

This variable seems redundant. Can't we use start directly and move the
'start = 0' to the bottom of the loop?

> + int size = min_t(int, copied, PAGE_SIZE - off);
> + start = 0;
> + if (i < MAX_SKB_FRAGS)
> + skb_fill_page_desc(skb, i, pages[n], off, size);
> + else
> + put_page(pages[n]);

Why is this condition needed, given we told iov_iter_get_pages() to
limit to MAX_SKB_FRAGS pages?

> + copied -= size;
> + i++, n++;
> + }
> + if (i > MAX_SKB_FRAGS)
> + return -EMSGSIZE;

Same here.

Ben.

> + }
> + return 0;
> +}
> +EXPORT_SYMBOL(zerocopy_sg_from_iter);
> +
> static int skb_copy_and_csum_datagram(const struct sk_buff *skb, int offset,
> u8 __user *to, int len,
> __wsum *csump)

--
Ben Hutchings
Never put off till tomorrow what you can avoid all together.
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