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Commit 2870c43d authored by Octavian Purdila's avatar Octavian Purdila Committed by David S. Miller
Browse files

net: refactor tcp splice receive path to improve readability 



- move all of the details on offsets, lengths and buffers into a
single function instead of doing these operation from multiple places

- use a bottom up approach: try to avoid details in the high level
functions, introduce them gradually as we go deeper in the function
call stack

With helpful feedback from Jarek Poplawski.

Signed-off-by: default avatarOctavian Purdila <opurdila@ixiacom.com>
Acked-by: default avatarJarek Poplawski <jarkao2@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent b9e40857

net/core/skbuff.c

+61 −92
Original line number Diff line number Diff line
@@ -1282,115 +1282,84 @@ static inline int spd_fill_page(struct splice_pipe_desc *spd, struct page *page, 
	return 0;

}



/*

 * Map linear and fragment data from the skb to spd. Returns number of

 * pages mapped.

 */

static int __skb_splice_bits(struct sk_buff *skb, unsigned int *offset,

			     unsigned int *total_len,

static inline void __segment_seek(struct page **page, unsigned int *poff,

				  unsigned int *plen, unsigned int off)

{

	*poff += off;

	*page += *poff / PAGE_SIZE;

	*poff = *poff % PAGE_SIZE;

	*plen -= off;

}



static inline int __splice_segment(struct page *page, unsigned int poff,

				   unsigned int plen, unsigned int *off,

				   unsigned int *len, struct sk_buff *skb,

				   struct splice_pipe_desc *spd)

{

	unsigned int nr_pages = spd->nr_pages;

	unsigned int poff, plen, len, toff, tlen;

	int headlen, seg, error = 0;

	if (!*len)

		return 1;



	toff = *offset;

	tlen = *total_len;

	if (!tlen) {

		error = 1;

		goto err;

	/* skip this segment if already processed */

	if (*off >= plen) {

		*off -= plen;

		return 0;

	}



	/*

	 * if the offset is greater than the linear part, go directly to

	 * the fragments.

	 */

	headlen = skb_headlen(skb);

	if (toff >= headlen) {

		toff -= headlen;

		goto map_frag;

	/* ignore any bits we already processed */

	if (*off) {

		__segment_seek(&page, &poff, &plen, *off);

		*off = 0;

	}



	/*

	 * first map the linear region into the pages/partial map, skipping

	 * any potential initial offset.

	 */

	len = 0;

	while (len < headlen) {

		void *p = skb->data + len;

	do {

		unsigned int flen = min(*len, plen);



		poff = (unsigned long) p & (PAGE_SIZE - 1);

		plen = min_t(unsigned int, headlen - len, PAGE_SIZE - poff);

		len += plen;

		/* the linear region may spread across several pages  */

		flen = min_t(unsigned int, flen, PAGE_SIZE - poff);



		if (toff) {

			if (plen <= toff) {

				toff -= plen;

				continue;

			}

			plen -= toff;

			poff += toff;

			toff = 0;

		}

		if (spd_fill_page(spd, page, flen, poff, skb))

			return 1;



		plen = min(plen, tlen);

		if (!plen)

			break;

		__segment_seek(&page, &poff, &plen, flen);

		*len -= flen;



	} while (*len && plen);



	return 0;

}



/*

		 * just jump directly to update and return, no point

		 * in going over fragments when the output is full.

 * Map linear and fragment data from the skb to spd. It reports failure if the

 * pipe is full or if we already spliced the requested length.

 */

		error = spd_fill_page(spd, virt_to_page(p), plen, poff, skb);

		if (error)

			goto done;

int __skb_splice_bits(struct sk_buff *skb, unsigned int *offset,

		      unsigned int *len,

		      struct splice_pipe_desc *spd)

{

	int seg;



		tlen -= plen;

	}

	/*

	 * map the linear part

	 */

	if (__splice_segment(virt_to_page(skb->data),

			     (unsigned long) skb->data & (PAGE_SIZE - 1),

			     skb_headlen(skb),

			     offset, len, skb, spd))

		return 1;



	/*

	 * then map the fragments

	 */

map_frag:

	for (seg = 0; seg < skb_shinfo(skb)->nr_frags; seg++) {

		const skb_frag_t *f = &skb_shinfo(skb)->frags[seg];



		plen = f->size;

		poff = f->page_offset;



		if (toff) {

			if (plen <= toff) {

				toff -= plen;

				continue;

			}

			plen -= toff;

			poff += toff;

			toff = 0;

		}



		plen = min(plen, tlen);

		if (!plen)

			break;



		error = spd_fill_page(spd, f->page, plen, poff, skb);

		if (error)

			break;



		tlen -= plen;

		if (__splice_segment(f->page, f->page_offset, f->size,

				     offset, len, skb, spd))

			return 1;

	}



done:

	if (spd->nr_pages - nr_pages) {

		*offset = 0;

		*total_len = tlen;

	return 0;

}

err:

	/* update the offset to reflect the linear part skip, if any */

	if (!error)

		*offset = toff;

	return error;

}



/*

 * Map data from the skb to a pipe. Should handle both the linear part,