1 files changed, 93 insertions, 0 deletions
diff --git a/iov.c b/iov.c
index 3741db2..4c6416c 100644
--- a/iov.c
+++ b/iov.c
@@ -155,3 +155,96 @@ size_t iov_size(const struct iovec *iov, size_t iov_cnt)
 
 	return len;
 }
+
+/**
+ * iov_tail_prune() - Remove any unneeded buffers from an IOV tail
+ * @tail:	IO vector tail (modified)
+ *
+ * If an IOV tail's offset is large enough, it may not include any bytes from
+ * the first (or first several) buffers in the underlying IO vector.  Modify the
+ * tail's representation so it contains the same logical bytes, but only
+ * includes buffers that are actually needed.  This will avoid stepping through
+ * unnecessary elements of the underlying IO vector on future operations.
+ *
+ * Return:	true if the tail still contains any bytes, otherwise false
+ */
+bool iov_tail_prune(struct iov_tail *tail)
+{
+	size_t i;
+
+	i = iov_skip_bytes(tail->iov, tail->cnt, tail->off, &tail->off);
+	tail->iov += i;
+	tail->cnt -= i;
+
+	return !!tail->cnt;
+}
+
+/**
+ * iov_tail_size - Calculate the total size of an IO vector tail
+ * @tail:	IO vector tail
+ *
+ * Returns:    The total size in bytes.
+ */
+/* cppcheck-suppress unusedFunction */
+size_t iov_tail_size(struct iov_tail *tail)
+{
+	iov_tail_prune(tail);
+	return iov_size(tail->iov, tail->cnt) - tail->off;
+}
+
+/**
+ * iov_peek_header_() - Get pointer to a header from an IOV tail
+ * @tail:	IOV tail to get header from
+ * @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, NULL if that
+ *	    overruns the IO vector, is not contiguous or doesn't have the
+ *	    requested alignment.
+ */
+void *iov_peek_header_(struct iov_tail *tail, size_t len, size_t align)
+{
+	char *p;
+
+	if (!iov_tail_prune(tail))
+		return NULL; /* Nothing left */
+
+	if (tail->off + len < tail->off)
+		return NULL; /* Overflow */
+
+	if (tail->off + len > tail->iov[0].iov_len)
+		return NULL; /* Not contiguous */
+
+	p = (char *)tail->iov[0].iov_base + tail->off;
+	if ((uintptr_t)p % align)
+		return NULL; /* not aligned */
+
+	return p;
+}
+
+/**
+ * iov_remove_header_() - Remove a header from an IOV tail
+ * @tail:	IOV tail to remove header from (modified)
+ * @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.
+ */
+/* cppcheck-suppress unusedFunction */
+void *iov_remove_header_(struct iov_tail *tail, size_t len, size_t align)
+{
+	char *p = iov_peek_header_(tail, len, align);
+
+	if (!p)
+		return NULL;
+
+	tail->off = tail->off + len;
+	return p;
+}