net: add skb_frag_foreach_page and use with kmap_atomic
Skb frags may contain compound pages. Various operations map frags
temporarily using kmap_atomic, but this function works on single
pages, not whole compound pages. The distinction is only relevant
for high mem pages that require temporary mappings.
Introduce a looping mechanism that for compound highmem pages maps
one page at a time, does not change behavior on other pages.
Use the loop in the kmap_atomic callers in net/core/skbuff.c.
Verified by triggering skb_copy_bits with
tcpdump -n -c 100 -i ${DEV} -w /dev/null &
netperf -t TCP_STREAM -H ${HOST}
and by triggering __skb_checksum with
ethtool -K ${DEV} tx off
repeated the tests with looping on a non-highmem platform
(x86_64) by making skb_frag_must_loop always return true.
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 18e76bf..6f9f1b2 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -345,6 +345,42 @@ static inline void skb_frag_size_sub(skb_frag_t *frag, int delta)
frag->size -= delta;
}
+static inline bool skb_frag_must_loop(struct page *p)
+{
+#if defined(CONFIG_HIGHMEM)
+ if (PageHighMem(p))
+ return true;
+#endif
+ return false;
+}
+
+/**
+ * skb_frag_foreach_page - loop over pages in a fragment
+ *
+ * @f: skb frag to operate on
+ * @f_off: offset from start of f->page.p
+ * @f_len: length from f_off to loop over
+ * @p: (temp var) current page
+ * @p_off: (temp var) offset from start of current page,
+ * non-zero only on first page.
+ * @p_len: (temp var) length in current page,
+ * < PAGE_SIZE only on first and last page.
+ * @copied: (temp var) length so far, excluding current p_len.
+ *
+ * A fragment can hold a compound page, in which case per-page
+ * operations, notably kmap_atomic, must be called for each
+ * regular page.
+ */
+#define skb_frag_foreach_page(f, f_off, f_len, p, p_off, p_len, copied) \
+ for (p = skb_frag_page(f) + ((f_off) >> PAGE_SHIFT), \
+ p_off = (f_off) & (PAGE_SIZE - 1), \
+ p_len = skb_frag_must_loop(p) ? \
+ min_t(u32, f_len, PAGE_SIZE - p_off) : f_len, \
+ copied = 0; \
+ copied < f_len; \
+ copied += p_len, p++, p_off = 0, \
+ p_len = min_t(u32, f_len - copied, PAGE_SIZE)) \
+
#define HAVE_HW_TIME_STAMP
/**