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Subject[PATCH v5 04/13] datagram: consolidate datagram copy to iter helpers
Date
From: Sagi Grimberg <sagi@lightbitslabs.com>

skb_copy_datagram_iter and skb_copy_and_csum_datagram are essentialy
the same but with a couple of differences: The first is the copy
operation used which either a simple copy or a csum_and_copy, and the
second are the behavior on the "short copy" path where simply copy
needs to return the number of bytes successfully copied while csum_and_copy
needs to fault immediately as the checksum is partial.

Introduce __skb_datagram_iter that additionally accepts:
1. copy operation function pointer
2. private data that goes with the copy operation
3. fault_short flag to indicate the action on short copy

Suggested-by: David S. Miller <davem@davemloft.net>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sagi Grimberg <sagi@lightbitslabs.com>
---
net/core/datagram.c | 136 ++++++++++++++------------------------------
1 file changed, 42 insertions(+), 94 deletions(-)

diff --git a/net/core/datagram.c b/net/core/datagram.c
index abe642181b64..382543302ae5 100644
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -408,27 +408,20 @@ int skb_kill_datagram(struct sock *sk, struct sk_buff *skb, unsigned int flags)
}
EXPORT_SYMBOL(skb_kill_datagram);

-/**
- * skb_copy_datagram_iter - Copy a datagram to an iovec iterator.
- * @skb: buffer to copy
- * @offset: offset in the buffer to start copying from
- * @to: iovec iterator to copy to
- * @len: amount of data to copy from buffer to iovec
- */
-int skb_copy_datagram_iter(const struct sk_buff *skb, int offset,
- struct iov_iter *to, int len)
+int __skb_datagram_iter(const struct sk_buff *skb, int offset,
+ struct iov_iter *to, int len, bool fault_short,
+ size_t (*cb)(const void *, size_t, void *, struct iov_iter *),
+ void *data)
{
int start = skb_headlen(skb);
int i, copy = start - offset, start_off = offset, n;
struct sk_buff *frag_iter;

- trace_skb_copy_datagram_iovec(skb, len);
-
/* Copy header. */
if (copy > 0) {
if (copy > len)
copy = len;
- n = copy_to_iter(skb->data + offset, copy, to);
+ n = cb(skb->data + offset, copy, data, to);
offset += n;
if (n != copy)
goto short_copy;
@@ -450,8 +443,8 @@ int skb_copy_datagram_iter(const struct sk_buff *skb, int offset,

if (copy > len)
copy = len;
- n = copy_to_iter(vaddr + frag->page_offset +
- offset - start, copy, to);
+ n = cb(vaddr + frag->page_offset +
+ offset - start, copy, data, to);
kunmap(page);
offset += n;
if (n != copy)
@@ -471,8 +464,8 @@ int skb_copy_datagram_iter(const struct sk_buff *skb, int offset,
if ((copy = end - offset) > 0) {
if (copy > len)
copy = len;
- if (skb_copy_datagram_iter(frag_iter, offset - start,
- to, copy))
+ if (__skb_datagram_iter(frag_iter, offset - start,
+ to, copy, short_copy, cb, data))
goto fault;
if ((len -= copy) == 0)
return 0;
@@ -493,11 +486,32 @@ int skb_copy_datagram_iter(const struct sk_buff *skb, int offset,
return -EFAULT;

short_copy:
- if (iov_iter_count(to))
+ if (fault_short || iov_iter_count(to))
goto fault;

return 0;
}
+
+static size_t simple_copy_to_iter(const void *addr, size_t bytes,
+ void *data __always_unused, struct iov_iter *i)
+{
+ return copy_to_iter(addr, bytes, i);
+}
+
+/**
+ * skb_copy_datagram_iter - Copy a datagram to an iovec iterator.
+ * @skb: buffer to copy
+ * @offset: offset in the buffer to start copying from
+ * @to: iovec iterator to copy to
+ * @len: amount of data to copy from buffer to iovec
+ */
+int skb_copy_datagram_iter(const struct sk_buff *skb, int offset,
+ struct iov_iter *to, int len)
+{
+ trace_skb_copy_datagram_iovec(skb, len);
+ return __skb_datagram_iter(skb, offset, to, len, false,
+ simple_copy_to_iter, NULL);
+}
EXPORT_SYMBOL(skb_copy_datagram_iter);

/**
@@ -648,87 +662,21 @@ int zerocopy_sg_from_iter(struct sk_buff *skb, struct iov_iter *from)
}
EXPORT_SYMBOL(zerocopy_sg_from_iter);

+/**
+ * skb_copy_and_csum_datagram_iter - Copy datagram to an iovec iterator
+ * and update a checksum.
+ * @skb: buffer to copy
+ * @offset: offset in the buffer to start copying from
+ * @to: iovec iterator to copy to
+ * @len: amount of data to copy from buffer to iovec
+ * @csump: checksum pointer
+ */
static int skb_copy_and_csum_datagram(const struct sk_buff *skb, int offset,
struct iov_iter *to, int len,
__wsum *csump)
{
- int start = skb_headlen(skb);
- int i, copy = start - offset, start_off = offset;
- struct sk_buff *frag_iter;
- int pos = 0;
- int n;
-
- /* Copy header. */
- if (copy > 0) {
- if (copy > len)
- copy = len;
- n = csum_and_copy_to_iter(skb->data + offset, copy, csump, to);
- offset += n;
- if (n != copy)
- goto fault;
- if ((len -= copy) == 0)
- return 0;
- pos = copy;
- }
-
- for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
- int end;
- const skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
-
- WARN_ON(start > offset + len);
-
- end = start + skb_frag_size(frag);
- if ((copy = end - offset) > 0) {
- __wsum csum2 = 0;
- struct page *page = skb_frag_page(frag);
- u8 *vaddr = kmap(page);
-
- if (copy > len)
- copy = len;
- n = csum_and_copy_to_iter(vaddr + frag->page_offset +
- offset - start, copy,
- &csum2, to);
- kunmap(page);
- offset += n;
- if (n != copy)
- goto fault;
- *csump = csum_block_add(*csump, csum2, pos);
- if (!(len -= copy))
- return 0;
- pos += copy;
- }
- start = end;
- }
-
- skb_walk_frags(skb, frag_iter) {
- int end;
-
- WARN_ON(start > offset + len);
-
- end = start + frag_iter->len;
- if ((copy = end - offset) > 0) {
- __wsum csum2 = 0;
- if (copy > len)
- copy = len;
- if (skb_copy_and_csum_datagram(frag_iter,
- offset - start,
- to, copy,
- &csum2))
- goto fault;
- *csump = csum_block_add(*csump, csum2, pos);
- if ((len -= copy) == 0)
- return 0;
- offset += copy;
- pos += copy;
- }
- start = end;
- }
- if (!len)
- return 0;
-
-fault:
- iov_iter_revert(to, offset - start_off);
- return -EFAULT;
+ return __skb_datagram_iter(skb, offset, to, len, true,
+ csum_and_copy_to_iter, csump);
}

__sum16 __skb_checksum_complete_head(struct sk_buff *skb, int len)
--
2.17.1
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