iov: Update IOV_REMOVE_HEADER() and IOV_PEEK_HEADER()

Provide a temporary variable of the wanted type to store
the header if the memory in the iovec array is not contiguous.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

3 files changed, 66 insertions, 24 deletions

diff --git a/iov.c b/iov.c
index 9a91eb6..d20fbb8 100644
--- a/iov.c
+++ b/iov.c
@@ -109,7 +109,7 @@ size_t iov_from_buf(const struct iovec *iov, size_t iov_cnt,
  *
  * Return: the number of bytes successfully copied.
  */
-/* cppcheck-suppress unusedFunction */
+/* cppcheck-suppress [staticFunction] */
 size_t iov_to_buf(const struct iovec *iov, size_t iov_cnt,
 		  size_t offset, void *buf, size_t bytes)
 {
@@ -127,6 +127,7 @@ size_t iov_to_buf(const struct iovec *iov, size_t iov_cnt,
 	/* copying data */
 	for (copied = 0; copied < bytes && i < iov_cnt; i++) {
 		size_t len = MIN(iov[i].iov_len - offset, bytes - copied);
+		ASSERT(iov[i].iov_base);
 		memcpy((char *)buf + copied, (char *)iov[i].iov_base + offset,
 		       len);
 		copied += len;
@@ -208,7 +209,7 @@ bool iov_drop_header(struct iov_tail *tail, size_t len)
 }
 
 /**
- * iov_peek_header_() - Get pointer to a header from an IOV tail
+ * iov_check_header() - Check if a header can be accessed
  * @tail:	IOV tail to get header from
  * @len:	Length of header to get, in bytes
  * @align:	Required alignment of header, in bytes
@@ -219,8 +220,7 @@ bool iov_drop_header(struct iov_tail *tail, size_t len)
  *	   overruns the IO vector, is not contiguous or doesn't have the
  *	   requested alignment.
  */
-/* cppcheck-suppress [staticFunction,unmatchedSuppression] */
-void *iov_peek_header_(struct iov_tail *tail, size_t len, size_t align)
+static void *iov_check_header(struct iov_tail *tail, size_t len, size_t align)
 {
 	char *p;
 
@@ -241,26 +241,61 @@ void *iov_peek_header_(struct iov_tail *tail, size_t len, size_t align)
 }
 
 /**
+ * iov_peek_header_() - Get pointer to a header from an IOV tail
+ * @tail:	IOV tail to get header from
+ * @v:		Temporary memory to use if the memory in @tail
+ *		is discontinuous
+ * @len:	Length of header to get, in bytes
+ * @align:	Required alignment of header, in bytes
+ *
+ * @tail may be pruned, but will represent the same bytes as before.
+ *
+ * Return: pointer to the first @len logical bytes of the tail, or to
+ *         a copy if that overruns the IO vector, is not contiguous or
+ *         doesn't have the requested alignment. NULL if that overruns the
+ *         IO vector.
+ */
+/* cppcheck-suppress [staticFunction,unmatchedSuppression] */
+void *iov_peek_header_(struct iov_tail *tail, void *v, size_t len, size_t align)
+{
+	char *p = iov_check_header(tail, len, align);
+	size_t l;
+
+	if (p)
+		return p;
+
+	l = iov_to_buf(tail->iov, tail->cnt, tail->off, v, len);
+	if (l != len)
+		return NULL;
+
+	return v;
+}
+
+/**
  * iov_remove_header_() - Remove a header from an IOV tail
  * @tail:	IOV tail to remove header from (modified)
+ * @v:		Temporary memory to use if the memory in @tail
+ *		is discontinuous
  * @len:	Length of header to remove, in bytes
  * @align:	Required alignment of header, in bytes
  *
  * On success, @tail is updated so that it longer includes the bytes of the
  * returned header.
  *
- * Return: pointer to the first @len logical bytes of the tail, NULL if that
- *	   overruns the IO vector, is not contiguous or doesn't have the
- *	   requested alignment.
+ * Return: pointer to the first @len logical bytes of the tail, or to
+ *         a copy if that overruns the IO vector, is not contiguous or
+ *         doesn't have the requested alignment. NULL if that overruns the
+ *         IO vector.
  */
-void *iov_remove_header_(struct iov_tail *tail, size_t len, size_t align)
+void *iov_remove_header_(struct iov_tail *tail, void *v, size_t len, size_t align)
 {
-	char *p = iov_peek_header_(tail, len, align);
+	char *p = iov_peek_header_(tail, v, len, align);
 
 	if (!p)
 		return NULL;
 
 	tail->off = tail->off + len;
+
 	return p;
 }
 
diff --git a/iov.h b/iov.h
index c94fabe..1821b40 100644
--- a/iov.h
+++ b/iov.h
@@ -73,38 +73,45 @@ struct iov_tail {
 bool iov_tail_prune(struct iov_tail *tail);
 size_t iov_tail_size(struct iov_tail *tail);
 bool iov_drop_header(struct iov_tail *tail, size_t len);
-void *iov_peek_header_(struct iov_tail *tail, size_t len, size_t align);
-void *iov_remove_header_(struct iov_tail *tail, size_t len, size_t align);
+void *iov_peek_header_(struct iov_tail *tail, void *v, size_t len, size_t align);
+void *iov_remove_header_(struct iov_tail *tail, void *v, size_t len, size_t align);
 ssize_t iov_tail_clone(struct iovec *dst_iov, size_t dst_iov_cnt,
 		       struct iov_tail *tail);
 
 /**
  * IOV_PEEK_HEADER() - Get typed pointer to a header from an IOV tail
  * @tail_:	IOV tail to get header from
- * @type_:	Data type of the header
+ * @var_:	Temporary buffer of the type of the header to use if
+ *		the memory in the iovec array is not contiguous.
  *
  * @tail_ may be pruned, but will represent the same bytes as before.
  *
- * Return: pointer of type (@type_ *) located at the start of @tail_, NULL if
- *         we can't get a contiguous and aligned pointer.
+ * Return: pointer of type (@type_ *) located at the start of @tail_
+ *         or to @var_ if iovec memory is not contiguous, NULL if
+ *         that overruns the iovec.
  */
-#define IOV_PEEK_HEADER(tail_, type_)					\
-	((type_ *)(iov_peek_header_((tail_),				\
-				    sizeof(type_), __alignof__(type_))))
+
+#define IOV_PEEK_HEADER(tail_, var_)					\
+	((__typeof__(var_) *)(iov_peek_header_((tail_), &(var_),	\
+					       sizeof(var_),		\
+					       __alignof__(var_))))
 
 /**
  * IOV_REMOVE_HEADER() - Remove and return typed header from an IOV tail
  * @tail_:	IOV tail to remove header from (modified)
- * @type_:	Data type of the header to remove
+ * @var_:	Temporary buffer of the type of the header to use if
+ *		the memory in the iovec array is not contiguous.
  *
  * On success, @tail_ is updated so that it longer includes the bytes of the
  * returned header.
  *
- * Return: pointer of type (@type_ *) located at the old start of @tail_, NULL
- *         if we can't get a contiguous and aligned pointer.
+ * Return: pointer of type (@type_ *) located at the start of @tail_
+ *         or to @var_ if iovec memory is not contiguous, NULL if
+ *         that overruns the iovec.
  */
-#define IOV_REMOVE_HEADER(tail_, type_)					\
-	((type_ *)(iov_remove_header_((tail_),				\
-				      sizeof(type_), __alignof__(type_))))
+
+#define IOV_REMOVE_HEADER(tail_, var_)					\
+	((__typeof__(var_) *)(iov_remove_header_((tail_), &(var_),	\
+				    sizeof(var_), __alignof__(var_))))
 
 #endif /* IOVEC_H */
diff --git a/tcp_buf.c b/tcp_buf.c
index d1fca67..bc898de 100644
--- a/tcp_buf.c
+++ b/tcp_buf.c
@@ -160,7 +160,7 @@ static void tcp_l2_buf_fill_headers(const struct tcp_tap_conn *conn,
 				    uint32_t seq, bool no_tcp_csum)
 {
 	struct iov_tail tail = IOV_TAIL(&iov[TCP_IOV_PAYLOAD], 1, 0);
-	struct tcphdr *th = IOV_REMOVE_HEADER(&tail, struct tcphdr);
+	struct tcphdr th_storage, *th = IOV_REMOVE_HEADER(&tail, th_storage);
 	struct tap_hdr *taph = iov[TCP_IOV_TAP].iov_base;
 	const struct flowside *tapside = TAPFLOW(conn);
 	const struct in_addr *a4 = inany_v4(&tapside->oaddr);