static int gve_tx_add_skb_no_copy()

in google/gve/gve_tx.c [640:739]

• 78 lines of code
• 12 McCabe index (conditional complexity)

static int gve_tx_add_skb_no_copy(struct gve_priv *priv, struct gve_tx_ring *tx,
				  struct sk_buff *skb)
{
	const struct skb_shared_info *shinfo = skb_shinfo(skb);
	int hlen, num_descriptors, l4_hdr_offset;
	union gve_tx_desc *pkt_desc, *mtd_desc, *seg_desc;
	struct gve_tx_buffer_state *info;
	int mtd_desc_nr = !!skb->l4_hash;
	bool is_gso = skb_is_gso(skb);
	u32 idx = tx->req & tx->mask;
	u64 addr;
	u32 len;
	int i;

	info = &tx->info[idx];
	pkt_desc = &tx->desc[idx];

	l4_hdr_offset = skb_checksum_start_offset(skb);
	/* If the skb is gso, then we want only up to the tcp header in the first segment
	 * to efficiently replicate on each segment otherwise we want the linear portion
	 * of the skb (which will contain the checksum because skb->csum_start and
	 * skb->csum_offset are given relative to skb->head) in the first segment.
	 */
	hlen = is_gso ? l4_hdr_offset + tcp_hdrlen(skb) : skb_headlen(skb);
	len = skb_headlen(skb);

	info->skb =  skb;

	addr = dma_map_single(tx->dev, skb->data, len, DMA_TO_DEVICE);
	if (unlikely(dma_mapping_error(tx->dev, addr))) {
		tx->dma_mapping_error++;
		goto drop;
	}
	dma_unmap_len_set(info, len, len);
	dma_unmap_addr_set(info, dma, addr);

	num_descriptors = 1 + shinfo->nr_frags;
	if (hlen < len)
		num_descriptors++;
	if (mtd_desc_nr)
		num_descriptors++;

	gve_tx_fill_pkt_desc(pkt_desc, skb->csum_offset, skb->ip_summed,
			     is_gso, l4_hdr_offset,
			     num_descriptors, hlen, addr, skb->len);

	if (mtd_desc_nr) {
		idx = (idx + 1) & tx->mask;
		mtd_desc = &tx->desc[idx];
		gve_tx_fill_mtd_desc(mtd_desc, skb);
	}

	if (hlen < len) {
		/* For gso the rest of the linear portion of the skb needs to
		 * be in its own descriptor.
		 */
		len -= hlen;
		addr += hlen;
		idx = (idx + 1) & tx->mask;
		seg_desc = &tx->desc[idx];
		gve_tx_fill_seg_desc(seg_desc, skb_network_offset(skb),
				     skb_shinfo(skb)->gso_size,
				     skb_is_gso_v6(skb), is_gso, len, addr);
	}

	for (i = 0; i < shinfo->nr_frags; i++) {
		const skb_frag_t *frag = &shinfo->frags[i];

		idx = (idx + 1) & tx->mask;
		seg_desc = &tx->desc[idx];
		len = skb_frag_size(frag);
		addr = skb_frag_dma_map(tx->dev, frag, 0, len, DMA_TO_DEVICE);
		if (unlikely(dma_mapping_error(tx->dev, addr))) {
			tx->dma_mapping_error++;
			goto unmap_drop;
		}
		tx->info[idx].skb = NULL;
		dma_unmap_len_set(&tx->info[idx], len, len);
		dma_unmap_addr_set(&tx->info[idx], dma, addr);

		gve_tx_fill_seg_desc(seg_desc, skb_network_offset(skb),
				     skb_shinfo(skb)->gso_size,
				     skb_is_gso_v6(skb), is_gso, len, addr);
	}

	return num_descriptors;

unmap_drop:
	i += num_descriptors - shinfo->nr_frags;
	while (i--) {
		/* Skip metadata descriptor, if set */
		if (i == 1 && mtd_desc_nr == 1)
			continue;
		idx--;
		gve_tx_unmap_buf(tx->dev, &tx->info[idx & tx->mask]);
	}
drop:
	tx->dropped_pkt++;
	return 0;
}