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: Octavian Purdila <opurdila@ixiacom.com>
Acked-by: Jarek Poplawski <jarkao2@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 50a853f..48a4372 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -1282,114 +1282,83 @@
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,
- struct splice_pipe_desc *spd)
+static inline void __segment_seek(struct page **page, unsigned int *poff,
+ unsigned int *plen, unsigned int off)
{
- unsigned int nr_pages = spd->nr_pages;
- unsigned int poff, plen, len, toff, tlen;
- int headlen, seg, error = 0;
+ *poff += off;
+ *page += *poff / PAGE_SIZE;
+ *poff = *poff % PAGE_SIZE;
+ *plen -= off;
+}
- toff = *offset;
- tlen = *total_len;
- if (!tlen) {
- error = 1;
- goto err;
+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)
+{
+ if (!*len)
+ return 1;
+
+ /* skip this segment if already processed */
+ if (*off >= plen) {
+ *off -= plen;
+ return 0;
}
+ /* ignore any bits we already processed */
+ if (*off) {
+ __segment_seek(&page, &poff, &plen, *off);
+ *off = 0;
+ }
+
+ do {
+ unsigned int flen = min(*len, plen);
+
+ /* the linear region may spread across several pages */
+ flen = min_t(unsigned int, flen, PAGE_SIZE - poff);
+
+ if (spd_fill_page(spd, page, flen, poff, skb))
+ return 1;
+
+ __segment_seek(&page, &poff, &plen, flen);
+ *len -= flen;
+
+ } while (*len && plen);
+
+ return 0;
+}
+
+/*
+ * 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.
+ */
+int __skb_splice_bits(struct sk_buff *skb, unsigned int *offset,
+ unsigned int *len,
+ struct splice_pipe_desc *spd)
+{
+ int seg;
+
/*
- * if the offset is greater than the linear part, go directly to
- * the fragments.
+ * map the linear part
*/
- headlen = skb_headlen(skb);
- if (toff >= headlen) {
- toff -= headlen;
- goto map_frag;
- }
-
- /*
- * 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;
-
- poff = (unsigned long) p & (PAGE_SIZE - 1);
- plen = min_t(unsigned int, headlen - len, PAGE_SIZE - poff);
- len += plen;
-
- if (toff) {
- if (plen <= toff) {
- toff -= plen;
- continue;
- }
- plen -= toff;
- poff += toff;
- toff = 0;
- }
-
- plen = min(plen, tlen);
- if (!plen)
- break;
-
- /*
- * just jump directly to update and return, no point
- * in going over fragments when the output is full.
- */
- error = spd_fill_page(spd, virt_to_page(p), plen, poff, skb);
- if (error)
- goto done;
-
- tlen -= plen;
- }
+ 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;
+ return 0;
}
/*