[ovs-dev] [netlink v5 05/61] netlink: New functions for finding a specific attribute.

[Ben Pfaff]

These functions are useful in the occasional case where a piece of code
only cares about one or a few attributes, probably knows that the format
is correct, and doesn't want to go to the trouble of doing a full parse.
Upcoming commits will add a user.

Reviewed by Justin Pettit.
---
 lib/netlink.c |   38 +++++++++++++++++++++++++++++++++++++-
 lib/netlink.h |    8 ++++++--
 2 files changed, 43 insertions(+), 3 deletions(-)

diff --git a/lib/netlink.c b/lib/netlink.c
index f1234ad..48a52ee 100644
--- a/lib/netlink.c
+++ b/lib/netlink.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008, 2009, 2010 Nicira Networks.
+ * Copyright (c) 2008, 2009, 2010, 2011 Nicira Networks.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -608,3 +608,39 @@ nl_parse_nested(const struct nlattr *nla, const struct nl_policy policy[],
     nl_attr_get_nested(nla, &buf);
     return nl_policy_parse(&buf, 0, policy, attrs, n_attrs);
 }
+
+static const struct nlattr *
+nl_attr_find__(const struct nlattr *attrs, size_t size, uint16_t type)
+{
+    const struct nlattr *nla;
+    size_t left;
+
+    NL_ATTR_FOR_EACH (nla, left, attrs, size) {
+        if (nl_attr_type (nla) == type) {
+            return nla;
+        }
+    }
+    return NULL;
+}
+
+/* Returns the first Netlink attribute within 'buf' with the specified 'type',
+ * skipping a header of 'hdr_len' bytes at the beginning of 'buf'.
+ *
+ * This function does not validate the attribute's length. */
+const struct nlattr *
+nl_attr_find(const struct ofpbuf *buf, size_t hdr_len, uint16_t type)
+{
+    const uint8_t *start = (const uint8_t *) buf->data + hdr_len;
+    return nl_attr_find__((const struct nlattr *) start, buf->size - hdr_len,
+                          type);
+}
+
+/* Returns the first Netlink attribute within 'nla' with the specified
+ * 'type'.
+ *
+ * This function does not validate the attribute's length. */
+const struct nlattr *
+nl_attr_find_nested(const struct nlattr *nla, uint16_t type)
+{
+    return nl_attr_find__(nl_attr_get(nla), nl_attr_get_size(nla), type);
+}
diff --git a/lib/netlink.h b/lib/netlink.h
index 383681c..5aa06a3 100644
--- a/lib/netlink.h
+++ b/lib/netlink.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008, 2009, 2010 Nicira Networks.
+ * Copyright (c) 2008, 2009, 2010, 2011 Nicira Networks.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -115,7 +115,7 @@ nl_attr_is_valid(const struct nlattr *nla, size_t maxlen)
 
 /* This macro does not check for attributes with bad lengths.  It should only
  * be used with messages from trusted sources or with messages that have
- * already been validates (e.g. with NL_ATTR_FOR_EACH).  */
+ * already been validated (e.g. with NL_ATTR_FOR_EACH).  */
 #define NL_ATTR_FOR_EACH_UNSAFE(ITER, LEFT, ATTRS, ATTRS_LEN)           \
     for ((ITER) = (ATTRS), (LEFT) = (ATTRS_LEN);                        \
          (LEFT) > 0;                                                    \
@@ -154,4 +154,8 @@ bool nl_policy_parse(const struct ofpbuf *, size_t offset,
 bool nl_parse_nested(const struct nlattr *, const struct nl_policy[],
                      struct nlattr *[], size_t n_attrs);
 
+const struct nlattr *nl_attr_find(const struct ofpbuf *, size_t hdr_len,
+                                  uint16_t type);
+const struct nlattr *nl_attr_find_nested(const struct nlattr *, uint16_t type);
+
 #endif /* netlink.h */
-- 
1.7.1