net: devmem: support single IOV with sendmsg

sendmsg() with a single iov becomes ITER_UBUF, sendmsg() with multiple
iovs becomes ITER_IOVEC. iter_iov_len does not return correct
value for UBUF, so teach to treat UBUF differently.

Cc: Al Viro <[email protected]>
Cc: Pavel Begunkov <[email protected]>
Cc: Mina Almasry <[email protected]>
Fixes: bd61848 ("net: devmem: Implement TX path")
Signed-off-by: Stanislav Fomichev <[email protected]>
Acked-by: Mina Almasry <[email protected]>
Reviewed-by: Pavel Begunkov <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

Author: Stanislav Fomichev

include/linux/uio.h

@@ -99,7 +99,13 @@ static inline const struct iovec *iter_iov(const struct iov_iter *iter)
 }
 
 #define iter_iov_addr(iter)	(iter_iov(iter)->iov_base + (iter)->iov_offset)
-#define iter_iov_len(iter)	(iter_iov(iter)->iov_len - (iter)->iov_offset)
+
+static inline size_t iter_iov_len(const struct iov_iter *i)
+{
+	if (i->iter_type == ITER_UBUF)
+		return i->count;
+	return iter_iov(i)->iov_len - i->iov_offset;
+}
 
 static inline enum iter_type iov_iter_type(const struct iov_iter *i)
 {

net/core/datagram.c

@@ -702,7 +702,8 @@ zerocopy_fill_skb_from_devmem(struct sk_buff *skb, struct iov_iter *from,
 	 * iov_addrs are interpreted as an offset in bytes into the dma-buf to
 	 * send from. We do not support other iter types.
 	 */
-	if (iov_iter_type(from) != ITER_IOVEC)
+	if (iov_iter_type(from) != ITER_IOVEC &&
+	    iov_iter_type(from) != ITER_UBUF)
 		return -EFAULT;
 
 	while (length && iov_iter_count(from)) {