packet: Rework packet_get() versus packet_get_try()

Most failures of packet_get() indicate a serious problem, and log messages
accordingly.  However, a few callers expect failures here, because they're
probing for a certain range which might or might not be in a packet.  They
use packet_get_try() which passes a NULL func to packet_get_do() to
suppress the logging which is unwanted in this case.

However, this doesn't just suppress the log when packet_get_do() finds the
requested region isn't in the packet.  It suppresses logging for all other
errors too, which do indicate serious problems, even for the callers of
packet_get_try().  Worse it will pass the NULL func on to
packet_check_range() which doesn't expect it, meaning we'll get unhelpful
messages from there if there is a failure.

Fix this by making packet_get_try_do() the primary function which doesn't
log for the case of a range outside the packet.  packet_get_do() becomes a
trivial wrapper around that which logs a message if packet_get_try_do()
returns NULL.

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

2 files changed, 40 insertions, 19 deletions

diff --git a/packet.c b/packet.c
index 7cbe95d..b3e8c79 100644
--- a/packet.c
+++ b/packet.c
@@ -89,7 +89,7 @@ bool pool_full(const struct pool *p)
  * @p:		Existing pool
  * @len:	Length of new descriptor
  * @start:	Start of data
- * @func:	For tracing: name of calling function, NULL means no trace()
+ * @func:	For tracing: name of calling function
  * @line:	For tracing: caller line of function call
  */
 void packet_add_do(struct pool *p, size_t len, const char *start,
@@ -113,39 +113,31 @@ void packet_add_do(struct pool *p, size_t len, const char *start,
 }
 
 /**
- * packet_get_do() - Get data range from packet descriptor from given pool
+ * packet_get_try_do() - Get data range from packet descriptor from given pool
  * @p:		Packet pool
  * @idx:	Index of packet descriptor in pool
  * @offset:	Offset of data range in packet descriptor
  * @len:	Length of desired data range
  * @left:	Length of available data after range, set on return, can be NULL
- * @func:	For tracing: name of calling function, NULL means no trace()
+ * @func:	For tracing: name of calling function
  * @line:	For tracing: caller line of function call
  *
  * Return: pointer to start of data range, NULL on invalid range or descriptor
  */
-void *packet_get_do(const struct pool *p, size_t idx, size_t offset,
-		    size_t len, size_t *left, const char *func, int line)
+void *packet_get_try_do(const struct pool *p, size_t idx, size_t offset,
+			size_t len, size_t *left, const char *func, int line)
 {
 	char *ptr;
 
 	if (idx >= p->size || idx >= p->count) {
-		if (func) {
-			trace("packet %zu from pool size: %zu, count: %zu, "
-			      "%s:%i", idx, p->size, p->count, func, line);
-		}
+		trace("packet %zu from pool size: %zu, count: %zu, %s:%i",
+		      idx, p->size, p->count, func, line);
 		return NULL;
 	}
 
 	if (offset > p->pkt[idx].iov_len ||
-	    len > (p->pkt[idx].iov_len - offset)) {
-		if (func) {
-			trace("data length %zu, offset %zu from length %zu, "
-			      "%s:%i", len, offset, p->pkt[idx].iov_len,
-			      func, line);
-		}
+	    len > (p->pkt[idx].iov_len - offset))
 		return NULL;
-	}
 
 	ptr = (char *)p->pkt[idx].iov_base + offset;
 
@@ -159,6 +151,33 @@ void *packet_get_do(const struct pool *p, size_t idx, size_t offset,
 }
 
 /**
+ * packet_get_do() - Get data range from packet descriptor from given pool
+ * @p:		Packet pool
+ * @idx:	Index of packet descriptor in pool
+ * @offset:	Offset of data range in packet descriptor
+ * @len:	Length of desired data range
+ * @left:	Length of available data after range, set on return, can be NULL
+ * @func:	For tracing: name of calling function
+ * @line:	For tracing: caller line of function call
+ *
+ * Return: as packet_get_try_do() but log a trace message when returning NULL
+ */
+void *packet_get_do(const struct pool *p, const size_t idx,
+		    size_t offset, size_t len, size_t *left,
+		    const char *func, int line)
+{
+	void *r = packet_get_try_do(p, idx, offset, len, left, func, line);
+
+	if (!r) {
+		trace("missing packet data length %zu, offset %zu from "
+		      "length %zu, %s:%i",
+		      len, offset, p->pkt[idx].iov_len, func, line);
+	}
+
+	return r;
+}
+
+/**
  * pool_flush() - Flush a packet pool
  * @p:		Pointer to packet pool
  */
diff --git a/packet.h b/packet.h
index 9061dad..c94780a 100644
--- a/packet.h
+++ b/packet.h
@@ -32,6 +32,9 @@ struct pool {
 int vu_packet_check_range(void *buf, const char *ptr, size_t len);
 void packet_add_do(struct pool *p, size_t len, const char *start,
 		   const char *func, int line);
+void *packet_get_try_do(const struct pool *p, const size_t idx,
+			size_t offset, size_t len, size_t *left,
+			const char *func, int line);
 void *packet_get_do(const struct pool *p, const size_t idx,
 		    size_t offset, size_t len, size_t *left,
 		    const char *func, int line);
@@ -41,12 +44,11 @@ void pool_flush(struct pool *p);
 #define packet_add(p, len, start)					\
 	packet_add_do(p, len, start, __func__, __LINE__)
 
+#define packet_get_try(p, idx, offset, len, left)			\
+	packet_get_try_do(p, idx, offset, len, left, __func__, __LINE__)
 #define packet_get(p, idx, offset, len, left)				\
 	packet_get_do(p, idx, offset, len, left, __func__, __LINE__)
 
-#define packet_get_try(p, idx, offset, len, left)			\
-	packet_get_do(p, idx, offset, len, left, NULL, 0)
-
 #define PACKET_POOL_DECL(_name, _size, _buf)				\
 struct _name ## _t {							\
 	char *buf;							\