From 7e86eef4a1d49b6f0e3c18633698ed7a601e9a73 Mon Sep 17 00:00:00 2001
From: Jacob Erlbeck <jerlbeck@sysmocom.de>
Date: Fri, 28 Feb 2014 20:11:21 +0100
Subject: msgb: Optionally declare some msgb struct fields as const

Writing directly to following struct fields may cause inconsistencies
that are hard to debug:

  data_len, len, head, tail, data

In general, the available macros and functions should be used to
modify them instead.

This patch declares these fields as const if
MSGB_DISABLE_DIRECT_WRITE is defined. Doing so may lead to warnings
and errors, therefore this macro is only defined for libosmocore yet,
where at least the errors are also fixed by this patch.

The main purpose is to maintain consistency, so only modifing the
fields themselves is restricted. It's still possible to modify the
data the pointers refer to.

Sponsored-by: On-Waves ehf
---
 include/osmocom/core/msgb.h | 66 +++++++++++++++++++++++++++++++--------------
 1 file changed, 46 insertions(+), 20 deletions(-)

(limited to 'include/osmocom/core/msgb.h')

diff --git a/include/osmocom/core/msgb.h b/include/osmocom/core/msgb.h
index 33e8081f..35933092 100644
--- a/include/osmocom/core/msgb.h
+++ b/include/osmocom/core/msgb.h
@@ -38,6 +38,12 @@
 
 #define MSGB_DEBUG
 
+#ifdef MSGB_DISABLE_DIRECT_WRITE
+#  define MSGB_CONST const
+#else
+#  define MSGB_CONST
+#endif
+
 /*! \brief Osmocom message buffer */
 struct msgb {
 	struct llist_head list; /*!< \brief linked list header */
@@ -58,12 +64,32 @@ struct msgb {
 
 	unsigned long cb[5]; /*!< \brief control buffer */
 
-	uint16_t data_len;   /*!< \brief length of underlying data array */
-	uint16_t len;	     /*!< \brief length of bytes used in msgb */
+	union {
+		/*! \brief length of underlying data array */
+		MSGB_CONST uint16_t data_len;
+		uint16_t __data_len;
+	};
+	union {
+		/*! \brief length of bytes used in msgb */
+		MSGB_CONST uint16_t len;
+		uint16_t __len;
+	};
+	union {
+		/*! \brief start of underlying memory buffer */
+		unsigned char * MSGB_CONST head;
+		unsigned char *__head;
+	};
+	union {
+		/*! \brief end of message in buffer */
+		unsigned char * MSGB_CONST tail;
+		unsigned char *__tail;
+	};
+	union {
+		/*! \brief start of message in buffer */
+		unsigned char * MSGB_CONST data;
+		unsigned char *__data;
+	};
 
-	unsigned char *head;	/*!< \brief start of underlying memory buffer */
-	unsigned char *tail;	/*!< \brief end of message in buffer */
-	unsigned char *data;	/*!< \brief start of message in buffer */
 	unsigned char _data[0]; /*!< \brief optional immediate data array */
 };
 
@@ -179,12 +205,12 @@ static inline int msgb_headroom(const struct msgb *msgb)
  */
 static inline unsigned char *msgb_put(struct msgb *msgb, unsigned int len)
 {
-	unsigned char *tmp = msgb->tail;
+	unsigned char *tmp = msgb->__tail;
 	if (msgb_tailroom(msgb) < (int) len)
 		MSGB_ABORT(msgb, "Not enough tailroom msgb_push (%u < %u)\n",
 			   msgb_tailroom(msgb), len);
-	msgb->tail += len;
-	msgb->len += len;
+	msgb->__tail += len;
+	msgb->__len += len;
 	return tmp;
 }
 
@@ -228,12 +254,12 @@ static inline void msgb_put_u32(struct msgb *msgb, uint32_t word)
  */
 static inline unsigned char *msgb_get(struct msgb *msgb, unsigned int len)
 {
-	unsigned char *tmp = msgb->data - len;
+	unsigned char *tmp = msgb->__data - len;
 	if (msgb_length(msgb) < len)
 		MSGB_ABORT(msgb, "msgb too small to get %u (len %u)\n",
 			   len, msgb_length(msgb));
-	msgb->tail -= len;
-	msgb->len -= len;
+	msgb->__tail -= len;
+	msgb->__len -= len;
 	return tmp;
 }
 /*! \brief remove uint8 from end of message
@@ -281,9 +307,9 @@ static inline unsigned char *msgb_push(struct msgb *msgb, unsigned int len)
 	if (msgb_headroom(msgb) < (int) len)
 		MSGB_ABORT(msgb, "Not enough headroom msgb_push (%u < %u)\n",
 			   msgb_headroom(msgb), len);
-	msgb->data -= len;
-	msgb->len += len;
-	return msgb->data;
+	msgb->__data -= len;
+	msgb->__len += len;
+	return msgb->__data;
 }
 /*! \brief remove (pull) a header from the front of the message buffer
  *  \param[in] msgb message buffer
@@ -296,8 +322,8 @@ static inline unsigned char *msgb_push(struct msgb *msgb, unsigned int len)
  */
 static inline unsigned char *msgb_pull(struct msgb *msgb, unsigned int len)
 {
-	msgb->len -= len;
-	return msgb->data += len;
+	msgb->__len -= len;
+	return msgb->__data += len;
 }
 
 /*! \brief remove (pull) all headers in front of l3h from the message buffer.
@@ -356,8 +382,8 @@ static inline uint32_t msgb_pull_u32(struct msgb *msgb)
  */
 static inline void msgb_reserve(struct msgb *msg, int len)
 {
-	msg->data += len;
-	msg->tail += len;
+	msg->__data += len;
+	msg->__tail += len;
 }
 
 /*! \brief Trim the msgb to a given absolute length
@@ -370,8 +396,8 @@ static inline int msgb_trim(struct msgb *msg, int len)
 	if (len > msg->data_len)
 		return -1;
 
-	msg->len = len;
-	msg->tail = msg->data + len;
+	msg->__len = len;
+	msg->__tail = msg->__data + len;
 
 	return 0;
 }
-- 
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