[ewg] Re: [PATCH] IPoIB 4K MTU support

[Roland Dreier]

Thanks, applied with some cleanups as below.

As an aside, in the case where we need to use a fragment in the receive
skb, does it make sense to make the initial linear part bigger so the
TCP and IP headers fit there (and the kernel doesn't have to look into
the fragment list to handle the packet)?

Also, is there any clean way where a kernel with PAGE_SIZE > 4096 can
have ud_need_sg evaluate to 0 at compile time, so that all the unneeded
code can be thrown out by the compiler?

 > +	return (IPOIB_UD_BUF_SIZE(ib_mtu) > PAGE_SIZE) ? 1 : 0;

I've never understood this style: it makes no sense to do

	return bool ? 1 : 0;

instead of just

	return bool;

 > +static inline void ipoib_ud_dma_unmap_rx(struct ipoib_dev_priv *priv,
 > +					 u64 mapping[IPOIB_UD_RX_SG])
 > +{
 > +	if (ipoib_ud_need_sg(priv->max_ib_mtu)) {
 > +		ib_dma_unmap_single(priv->ca, mapping[0], IPOIB_UD_HEAD_SIZE, DMA_FROM_DEVICE);
 > +		ib_dma_unmap_page(priv->ca, mapping[1], PAGE_SIZE, DMA_FROM_DEVICE);
 > +	} else
 > +		ib_dma_unmap_single(priv->ca, mapping[0], IPOIB_UD_BUF_SIZE(priv->max_ib_mtu), DMA_FROM_DEVICE);
 > +}
 > +
 > +static inline void ipoib_ud_skb_put_frags(struct ipoib_dev_priv *priv,
 > +					  struct sk_buff *skb,
 > +					  unsigned int length)
 > +{
 > +	if (ipoib_ud_need_sg(priv->max_ib_mtu)) {
 > +		skb_frag_t *frag = &skb_shinfo(skb)->frags[0];
 > +		/*
 > +		 * There is only two buffers needed for max_payload = 4K,
 > +		 * first buf size is IPOIB_UD_HEAD_SIZE
 > +		 */
 > +		skb->tail += IPOIB_UD_HEAD_SIZE;
 > +		frag->size = length - IPOIB_UD_HEAD_SIZE;
 > +		skb->data_len += frag->size;
 > +		skb->truesize += frag->size;
 > +		skb->len += length;
 > +	} else
 > +		skb_put(skb, length);
 > +
 > +}

These are pretty big to put in a header file as inlines... I moved them
to the only .c file where they're used.

 - R.