[PATCH v6 03/30] iov: Update IOV_REMOVE_HEADER() and IOV_PEEK_HEADER()

[Laurent Vivier <lvivier@redhat.com>]

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>
---
 iov.c     | 53 ++++++++++++++++++++++++++++++++++++++++++++---------
 iov.h     | 55 +++++++++++++++++++++++++++++++++++++++++--------------
 tcp_buf.c |  2 +-
 3 files changed, 86 insertions(+), 24 deletions(-)

diff --git a/iov.c b/iov.c
index 3b89f8126ee7..541ca8aa9119 100644
--- a/iov.c
+++ b/iov.c
@@ -109,7 +109,7 @@ size_t iov_from_buf(const struct iovec *iov, size_t iov_cnt,
  *
  * Returns:    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);
+		/* NOLINTNEXTLINE(clang-analyzer-core.NonNullParamChecker) */
 		memcpy((char *)buf + copied, (char *)iov[i].iov_base + offset,
 		       len);
 		copied += len;
@@ -208,7 +209,7 @@ bool iov_tail_drop(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_tail_drop(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;
 
@@ -240,27 +240,62 @@ void *iov_peek_header_(struct iov_tail *tail, size_t len, size_t align)
 	return p;
 }
 
+/**
+ * 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.
+ *
+ * Returns: 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.
  *
- * Returns: 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.
+ * Returns: 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 11a8567aa183..7d5bce2f841c 100644
--- a/iov.h
+++ b/iov.h
@@ -70,41 +70,68 @@ struct iov_tail {
 #define IOV_TAIL(iov_, cnt_, off_) \
 	(struct iov_tail){ .iov = (iov_), .cnt = (cnt_), .off = (off_) }
 
+/**
+ * IOV_TAIL_FROM_BUF() - Create a new IOV tail from a buffer
+ * @buf_:	Buffer address to use in the iovec
+ * @len_:	Buffer size
+ * @off_:	Byte offset in the buffer where the tail begins
+ */
+#define IOV_TAIL_FROM_BUF(buf_, len_, off_) \
+	IOV_TAIL((&(const struct iovec){ .iov_base = (buf_),		\
+					 .iov_len = (len_) }),		\
+		 1,							\
+		 (off_))
+
 bool iov_tail_prune(struct iov_tail *tail);
 size_t iov_tail_size(struct iov_tail *tail);
 bool iov_tail_drop(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.
  *
- * Returns: Pointer of type (@type_ *) located at the start of @tail_, NULL if
- *          we can't get a contiguous and aligned pointer.
+ * Returns: 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.
  *
- * Returns: Pointer of type (@type_ *) located at the old start of @tail_, NULL
- *          if we can't get a contiguous and aligned pointer.
+ * Returns: 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_, var_)					\
+	((__typeof__(var_) *)(iov_remove_header_((tail_), &(var_),	\
+				    sizeof(var_), __alignof__(var_))))
+
+/** IOV_DROP_HEADER() - Remove a typed header from an IOV tail
+ * @tail_:	IOV tail to remove header from (modified)
+ * @type_:	Data type of the header to remove
+ *
+ * Returns:	true if the tail still contains any bytes, otherwise false
  */
-#define IOV_REMOVE_HEADER(tail_, type_)					\
-	((type_ *)(iov_remove_header_((tail_),				\
-				      sizeof(type_), __alignof__(type_))))
+#define IOV_DROP_HEADER(tail_, type_) 	iov_tail_drop((tail_), sizeof(type_))
 
 #endif /* IOVEC_H */
diff --git a/tcp_buf.c b/tcp_buf.c
index 05305636b503..ac6d73130f55 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);
-- 
@@ -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);
-- 
2.49.0