[PATCH] lib: add const-ness to appropriate parameters in addr, attr, data

[Dan Williams]

On Fri, 2015-02-13 at 18:26 +0800, Rohan Joyce wrote:
> This patch changes the signatures of some functions to allow const pointers in
> places where a const qualified pointer is enough access for what the function
> does (e.g. nla_get_u8). It also changes some functions that take a pointer
> parameter and return a pointer derived from it to use the strchr idiom.
> 
> This is not exhaustive in terms of places where const can be added, but it's
> a decent chunk that should not make the external api any more restrictive. 

Though I think it'll break source compatibility at least?  eg something
built against libnl before this patch will no longer build after this
patch, potentially.  Just something to think about.

Dan

> Signed-off-by: Rohan Joyce <rojoyce.github at gmail.com>
> ---
>  include/netlink/addr.h | 39 ++++++++++++++++++-----------------
>  include/netlink/attr.h | 34 ++++++++++++++++---------------
>  include/netlink/data.h | 15 +++++++-------
>  lib/addr.c             | 40 ++++++++++++++++++------------------
>  lib/attr.c             | 55 +++++++++++++++++++++++++-------------------------
>  lib/data.c             | 22 +++++++++++---------
>  6 files changed, 107 insertions(+), 98 deletions(-)
> 
> diff --git a/include/netlink/addr.h b/include/netlink/addr.h
> index db3e4c2..9d0d24a 100644
> --- a/include/netlink/addr.h
> +++ b/include/netlink/addr.h
> @@ -22,42 +22,45 @@ struct nl_addr;
>  
>  /* Creation */
>  extern struct nl_addr *	nl_addr_alloc(size_t);
> -extern struct nl_addr *	nl_addr_alloc_attr(struct nlattr *, int);
> -extern struct nl_addr *	nl_addr_build(int, void *, size_t);
> +extern struct nl_addr *	nl_addr_alloc_attr(const struct nlattr *, int);
> +extern struct nl_addr *	nl_addr_build(int, const void *, size_t);
>  extern int		nl_addr_parse(const char *, int, struct nl_addr **);
> -extern struct nl_addr *	nl_addr_clone(struct nl_addr *);
> +extern struct nl_addr *	nl_addr_clone(const struct nl_addr *);
>  
>  /* Usage Management */
>  extern struct nl_addr *	nl_addr_get(struct nl_addr *);
>  extern void		nl_addr_put(struct nl_addr *);
> -extern int		nl_addr_shared(struct nl_addr *);
> +extern int		nl_addr_shared(const struct nl_addr *);
>  
> -extern int		nl_addr_cmp(struct nl_addr *, struct nl_addr *);
> -extern int		nl_addr_cmp_prefix(struct nl_addr *, struct nl_addr *);
> -extern int		nl_addr_iszero(struct nl_addr *);
> -extern int		nl_addr_valid(char *, int);
> -extern int      	nl_addr_guess_family(struct nl_addr *);
> -extern int		nl_addr_fill_sockaddr(struct nl_addr *,
> +extern int		nl_addr_cmp(const struct nl_addr *,
> +				    const struct nl_addr *);
> +extern int		nl_addr_cmp_prefix(const struct nl_addr *,
> +					   const struct nl_addr *);
> +extern int		nl_addr_iszero(const struct nl_addr *);
> +extern int		nl_addr_valid(const char *, int);
> +extern int      	nl_addr_guess_family(const struct nl_addr *);
> +extern int		nl_addr_fill_sockaddr(const struct nl_addr *,
>  					      struct sockaddr *, socklen_t *);
> -extern int		nl_addr_info(struct nl_addr *, struct addrinfo **);
> -extern int		nl_addr_resolve(struct nl_addr *, char *, size_t);
> +extern int		nl_addr_info(const struct nl_addr *,
> +				     struct addrinfo **);
> +extern int		nl_addr_resolve(const struct nl_addr *, char *, size_t);
>  
>  /* Access Functions */
>  extern void		nl_addr_set_family(struct nl_addr *, int);
> -extern int		nl_addr_get_family(struct nl_addr *);
> -extern int		nl_addr_set_binary_addr(struct nl_addr *, void *,
> +extern int		nl_addr_get_family(const struct nl_addr *);
> +extern int		nl_addr_set_binary_addr(struct nl_addr *, const void *,
>  						size_t);
> -extern void *		nl_addr_get_binary_addr(struct nl_addr *);
> -extern unsigned int	nl_addr_get_len(struct nl_addr *);
> +extern void *		nl_addr_get_binary_addr(const struct nl_addr *);
> +extern unsigned int	nl_addr_get_len(const struct nl_addr *);
>  extern void		nl_addr_set_prefixlen(struct nl_addr *, int);
> -extern unsigned int	nl_addr_get_prefixlen(struct nl_addr *);
> +extern unsigned int	nl_addr_get_prefixlen(const struct nl_addr *);
>  
>  /* Address Family Translations */
>  extern char *		nl_af2str(int, char *, size_t);
>  extern int		nl_str2af(const char *);
>  
>  /* Translations to Strings */
> -extern char *		nl_addr2str(struct nl_addr *, char *, size_t);
> +extern char *		nl_addr2str(const struct nl_addr *, char *, size_t);
>  
>  #ifdef __cplusplus
>  }
> diff --git a/include/netlink/attr.h b/include/netlink/attr.h
> index 82e4c38..b84b62e 100644
> --- a/include/netlink/attr.h
> +++ b/include/netlink/attr.h
> @@ -81,12 +81,12 @@ extern int		nla_ok(const struct nlattr *, int);
>  extern struct nlattr *	nla_next(const struct nlattr *, int *);
>  extern int		nla_parse(struct nlattr **, int, struct nlattr *,
>  				  int, struct nla_policy *);
> -extern int		nla_validate(struct nlattr *, int, int,
> -				     struct nla_policy *);
> -extern struct nlattr *	nla_find(struct nlattr *, int, int);
> +extern int		nla_validate(const struct nlattr *, int, int,
> +				     const struct nla_policy *);
> +extern struct nlattr *	nla_find(const struct nlattr *, int, int);
>  
>  /* Helper Functions */
> -extern int		nla_memcpy(void *, struct nlattr *, int);
> +extern int		nla_memcpy(void *, const struct nlattr *, int);
>  extern size_t		nla_strlcpy(char *, const struct nlattr *, size_t);
>  extern int		nla_memcmp(const struct nlattr *, const void *, size_t);
>  extern int		nla_strcmp(const struct nlattr *, const char *);
> @@ -94,40 +94,42 @@ extern int		nla_strcmp(const struct nlattr *, const char *);
>  /* Unspecific attribute */
>  extern struct nlattr *	nla_reserve(struct nl_msg *, int, int);
>  extern int		nla_put(struct nl_msg *, int, int, const void *);
> -extern int		nla_put_data(struct nl_msg *, int, struct nl_data *);
> +extern int		nla_put_data(struct nl_msg *, int,
> +				     const struct nl_data *);
>  extern int		nla_put_addr(struct nl_msg *, int, struct nl_addr *);
>  
>  /* Integer attribute */
> -extern uint8_t		nla_get_u8(struct nlattr *);
> +extern uint8_t		nla_get_u8(const struct nlattr *);
>  extern int		nla_put_u8(struct nl_msg *, int, uint8_t);
> -extern uint16_t		nla_get_u16(struct nlattr *);
> +extern uint16_t		nla_get_u16(const struct nlattr *);
>  extern int		nla_put_u16(struct nl_msg *, int, uint16_t);
> -extern uint32_t		nla_get_u32(struct nlattr *);
> +extern uint32_t		nla_get_u32(const struct nlattr *);
>  extern int		nla_put_u32(struct nl_msg *, int, uint32_t);
> -extern uint64_t		nla_get_u64(struct nlattr *);
> +extern uint64_t		nla_get_u64(const struct nlattr *);
>  extern int		nla_put_u64(struct nl_msg *, int, uint64_t);
>  
>  /* String attribute */
> -extern char *		nla_get_string(struct nlattr *);
> -extern char *		nla_strdup(struct nlattr *);
> +extern char *		nla_get_string(const struct nlattr *);
> +extern char *		nla_strdup(const struct nlattr *);
>  extern int		nla_put_string(struct nl_msg *, int, const char *);
>  
>  /* Flag attribute */
> -extern int		nla_get_flag(struct nlattr *);
> +extern int		nla_get_flag(const struct nlattr *);
>  extern int		nla_put_flag(struct nl_msg *, int);
>  
>  /* Msec attribute */
> -extern unsigned long	nla_get_msecs(struct nlattr *);
> +extern unsigned long	nla_get_msecs(const struct nlattr *);
>  extern int		nla_put_msecs(struct nl_msg *, int, unsigned long);
>  
>  /* Attribute nesting */
> -extern int		nla_put_nested(struct nl_msg *, int, struct nl_msg *);
> +extern int		nla_put_nested(struct nl_msg *, int,
> +				       const struct nl_msg *);
>  extern struct nlattr *	nla_nest_start(struct nl_msg *, int);
>  extern int		nla_nest_end(struct nl_msg *, struct nlattr *);
> -extern void		nla_nest_cancel(struct nl_msg *, struct nlattr *);
> +extern void		nla_nest_cancel(struct nl_msg *, const struct nlattr *);
>  extern int		nla_parse_nested(struct nlattr **, int, struct nlattr *,
>  					 struct nla_policy *);
> -extern int		nla_is_nested(struct nlattr *);
> +extern int		nla_is_nested(const struct nlattr *);
>  
>  /**
>   * @name Attribute Construction (Exception Based)
> diff --git a/include/netlink/data.h b/include/netlink/data.h
> index 071159e..b091c4b 100644
> --- a/include/netlink/data.h
> +++ b/include/netlink/data.h
> @@ -21,18 +21,19 @@ extern "C" {
>  struct nl_data;
>  
>  /* General */
> -extern struct nl_data *	nl_data_alloc(void *, size_t);
> -extern struct nl_data * nl_data_alloc_attr(struct nlattr *);
> -extern struct nl_data *	nl_data_clone(struct nl_data *);
> -extern int		nl_data_append(struct nl_data *, void *, size_t);
> +extern struct nl_data *	nl_data_alloc(const void *, size_t);
> +extern struct nl_data * nl_data_alloc_attr(const struct nlattr *);
> +extern struct nl_data *	nl_data_clone(const struct nl_data *);
> +extern int		nl_data_append(struct nl_data *, const void *, size_t);
>  extern void		nl_data_free(struct nl_data *);
>  
>  /* Access Functions */
> -extern void *		nl_data_get(struct nl_data *);
> -extern size_t		nl_data_get_size(struct nl_data *);
> +extern void *		nl_data_get(const struct nl_data *);
> +extern size_t		nl_data_get_size(const struct nl_data *);
>  
>  /* Misc */
> -extern int		nl_data_cmp(struct nl_data *, struct nl_data *);
> +extern int		nl_data_cmp(const struct nl_data *,
> +				    const struct nl_data *);
>  
>  #ifdef __cplusplus
>  }
> diff --git a/lib/addr.c b/lib/addr.c
> index d275948..3337878 100644
> --- a/lib/addr.c
> +++ b/lib/addr.c
> @@ -65,7 +65,7 @@ static inline int do_digit(char *str, uint16_t *addr, uint16_t scale,
>  	return 0;
>  }
>  
> -static const char *dnet_ntop(char *addrbuf, size_t addrlen, char *str,
> +static const char *dnet_ntop(const char *addrbuf, size_t addrlen, char *str,
>  			     size_t len)
>  {
>  	uint16_t addr = dn_ntohs(*(uint16_t *)addrbuf);
> @@ -213,7 +213,7 @@ struct nl_addr *nl_addr_alloc(size_t maxsize)
>   *
>   * @return Allocated address object or NULL upon failure.
>   */
> -struct nl_addr *nl_addr_build(int family, void *buf, size_t size)
> +struct nl_addr *nl_addr_build(int family, const void *buf, size_t size)
>  {
>  	struct nl_addr *addr;
>  
> @@ -252,7 +252,7 @@ struct nl_addr *nl_addr_build(int family, void *buf, size_t size)
>   *
>   * @return Allocated address object or NULL upon failure.
>   */
> -struct nl_addr *nl_addr_alloc_attr(struct nlattr *nla, int family)
> +struct nl_addr *nl_addr_alloc_attr(const struct nlattr *nla, int family)
>  {
>  	return nl_addr_build(family, nla_data(nla), nla_len(nla));
>  }
> @@ -468,7 +468,7 @@ errout:
>   *
>   * @return Allocated abstract address or NULL upon failure.
>   */
> -struct nl_addr *nl_addr_clone(struct nl_addr *addr)
> +struct nl_addr *nl_addr_clone(const struct nl_addr *addr)
>  {
>  	struct nl_addr *new;
>  
> @@ -531,7 +531,7 @@ void nl_addr_put(struct nl_addr *addr)
>   *
>   * @return Non-zero if the abstract address is shared, otherwise 0.
>   */
> -int nl_addr_shared(struct nl_addr *addr)
> +int nl_addr_shared(const struct nl_addr *addr)
>  {
>  	return addr->a_refcnt > 1;
>  }
> @@ -560,7 +560,7 @@ int nl_addr_shared(struct nl_addr *addr)
>   * @return Integer less than, equal to or greather than zero if the two
>   *         addresses match.
>   */
> -int nl_addr_cmp(struct nl_addr *a, struct nl_addr *b)
> +int nl_addr_cmp(const struct nl_addr *a, const struct nl_addr *b)
>  {
>  	int d = a->a_family - b->a_family;
>  
> @@ -591,7 +591,7 @@ int nl_addr_cmp(struct nl_addr *a, struct nl_addr *b)
>   * @return Integer less than, equal to or greather than zero if the two
>   *         addresses match.
>   */
> -int nl_addr_cmp_prefix(struct nl_addr *a, struct nl_addr *b)
> +int nl_addr_cmp_prefix(const struct nl_addr *a, const struct nl_addr *b)
>  {
>  	int d = a->a_family - b->a_family;
>  
> @@ -617,7 +617,7 @@ int nl_addr_cmp_prefix(struct nl_addr *a, struct nl_addr *b)
>   *
>   * @return 1 if the binary address consists of all zeros, 0 otherwise.
>   */
> -int nl_addr_iszero(struct nl_addr *addr)
> +int nl_addr_iszero(const struct nl_addr *addr)
>  {
>  	unsigned int i;
>  
> @@ -636,7 +636,7 @@ int nl_addr_iszero(struct nl_addr *addr)
>   * @return 1 if the address is parseable assuming the specified address family,
>   *         otherwise 0 is returned.
>   */
> -int nl_addr_valid(char *addr, int family)
> +int nl_addr_valid(const char *addr, int family)
>  {
>  	int ret;
>  	char buf[32];
> @@ -670,7 +670,7 @@ int nl_addr_valid(char *addr, int family)
>   *
>   * @return Numeric address family or AF_UNSPEC
>   */
> -int nl_addr_guess_family(struct nl_addr *addr)
> +int nl_addr_guess_family(const struct nl_addr *addr)
>  {
>  	switch (addr->a_len) {
>  		case 4:
> @@ -697,7 +697,7 @@ int nl_addr_guess_family(struct nl_addr *addr)
>   *
>   * @return 0 on success or a negative error code
>   */
> -int nl_addr_fill_sockaddr(struct nl_addr *addr, struct sockaddr *sa,
> +int nl_addr_fill_sockaddr(const struct nl_addr *addr, struct sockaddr *sa,
>  			  socklen_t *salen)
>  {
>  	switch (addr->a_family) {
> @@ -753,7 +753,7 @@ int nl_addr_fill_sockaddr(struct nl_addr *addr, struct sockaddr *sa,
>   *
>   * @return 0 on success or a negative error code.
>   */
> -int nl_addr_info(struct nl_addr *addr, struct addrinfo **result)
> +int nl_addr_info(const struct nl_addr *addr, struct addrinfo **result)
>  {
>  	int err;
>  	char buf[INET6_ADDRSTRLEN+5];
> @@ -797,7 +797,7 @@ int nl_addr_info(struct nl_addr *addr, struct addrinfo **result)
>   *
>   * @return 0 on success or a negative error code.
>   */
> -int nl_addr_resolve(struct nl_addr *addr, char *host, size_t hostlen)
> +int nl_addr_resolve(const struct nl_addr *addr, char *host, size_t hostlen)
>  {
>  	int err;
>  	struct sockaddr_in6 buf;
> @@ -842,7 +842,7 @@ void nl_addr_set_family(struct nl_addr *addr, int family)
>   *
>   * @return The numeric address family or `AF_UNSPEC`
>   */
> -int nl_addr_get_family(struct nl_addr *addr)
> +int nl_addr_get_family(const struct nl_addr *addr)
>  {
>  	return addr->a_family;
>  }
> @@ -867,7 +867,7 @@ int nl_addr_get_family(struct nl_addr *addr)
>   *
>   * @return 0 on success or a negative error code.
>   */
> -int nl_addr_set_binary_addr(struct nl_addr *addr, void *buf, size_t len)
> +int nl_addr_set_binary_addr(struct nl_addr *addr, const void *buf, size_t len)
>  {
>  	if (len > addr->a_maxsize)
>  		return -NLE_RANGE;
> @@ -890,9 +890,9 @@ int nl_addr_set_binary_addr(struct nl_addr *addr, void *buf, size_t len)
>   *
>   * @return Pointer to binary address of length nl_addr_get_len()
>   */
> -void *nl_addr_get_binary_addr(struct nl_addr *addr)
> +void *nl_addr_get_binary_addr(const struct nl_addr *addr)
>  {
> -	return addr->a_addr;
> +	return (void*)addr->a_addr;
>  }
>  
>  /**
> @@ -902,7 +902,7 @@ void *nl_addr_get_binary_addr(struct nl_addr *addr)
>   * @see nl_addr_get_binary_addr()
>   * @see nl_addr_set_binary_addr()
>   */
> -unsigned int nl_addr_get_len(struct nl_addr *addr)
> +unsigned int nl_addr_get_len(const struct nl_addr *addr)
>  {
>  	return addr->a_len;
>  }
> @@ -925,7 +925,7 @@ void nl_addr_set_prefixlen(struct nl_addr *addr, int prefixlen)
>   *
>   * @see nl_addr_set_prefixlen()
>   */
> -unsigned int nl_addr_get_prefixlen(struct nl_addr *addr)
> +unsigned int nl_addr_get_prefixlen(const struct nl_addr *addr)
>  {
>  	return addr->a_prefixlen;
>  }
> @@ -948,7 +948,7 @@ unsigned int nl_addr_get_prefixlen(struct nl_addr *addr)
>   *
>   * @return Address represented in ASCII stored in destination buffer.
>   */
> -char *nl_addr2str(struct nl_addr *addr, char *buf, size_t size)
> +char *nl_addr2str(const struct nl_addr *addr, char *buf, size_t size)
>  {
>  	unsigned int i;
>  	char tmp[16];
> diff --git a/lib/attr.c b/lib/attr.c
> index d1f0268..838d0a9 100644
> --- a/lib/attr.c
> +++ b/lib/attr.c
> @@ -185,10 +185,10 @@ static uint16_t nla_attr_minlen[NLA_TYPE_MAX+1] = {
>  	[NLA_FLAG]	= 0,
>  };
>  
> -static int validate_nla(struct nlattr *nla, int maxtype,
> -			struct nla_policy *policy)
> +static int validate_nla(const struct nlattr *nla, int maxtype,
> +			const struct nla_policy *policy)
>  {
> -	struct nla_policy *pt;
> +	const struct nla_policy *pt;
>  	unsigned int minlen = 0;
>  	int type = nla_type(nla);
>  
> @@ -212,7 +212,7 @@ static int validate_nla(struct nlattr *nla, int maxtype,
>  		return -NLE_RANGE;
>  
>  	if (pt->type == NLA_STRING) {
> -		char *data = nla_data(nla);
> +		const char *data = nla_data(nla);
>  		if (data[nla_len(nla) - 1] != '\0')
>  			return -NLE_INVAL;
>  	}
> @@ -291,10 +291,10 @@ errout:
>   *
>   * @return 0 on success or a negative error code.
>   */
> -int nla_validate(struct nlattr *head, int len, int maxtype,
> -		 struct nla_policy *policy)
> +int nla_validate(const struct nlattr *head, int len, int maxtype,
> +		 const struct nla_policy *policy)
>  {
> -	struct nlattr *nla;
> +	const struct nlattr *nla;
>  	int rem, err;
>  
>  	nla_for_each_attr(nla, head, len, rem) {
> @@ -320,14 +320,14 @@ errout:
>   *
>   * @return Pointer to attribute found or NULL.
>   */
> -struct nlattr *nla_find(struct nlattr *head, int len, int attrtype)
> +struct nlattr *nla_find(const struct nlattr *head, int len, int attrtype)
>  {
> -	struct nlattr *nla;
> +	const struct nlattr *nla;
>  	int rem;
>  
>  	nla_for_each_attr(nla, head, len, rem)
>  		if (nla_type(nla) == attrtype)
> -			return nla;
> +			return (struct nlattr*)nla;
>  
>  	return NULL;
>  }
> @@ -350,7 +350,7 @@ struct nlattr *nla_find(struct nlattr *head, int len, int attrtype)
>   *
>   * @return The number of bytes copied to dest.
>   */
> -int nla_memcpy(void *dest, struct nlattr *src, int count)
> +int nla_memcpy(void *dest, const struct nlattr *src, int count)
>  {
>  	int minlen;
>  
> @@ -378,7 +378,7 @@ int nla_memcpy(void *dest, struct nlattr *src, int count)
>  size_t nla_strlcpy(char *dst, const struct nlattr *nla, size_t dstsize)
>  {
>  	size_t srclen = nla_len(nla);
> -	char *src = nla_data(nla);
> +	const char *src = nla_data(nla);
>  
>  	if (srclen > 0 && src[srclen - 1] == '\0')
>  		srclen--;
> @@ -524,7 +524,7 @@ int nla_put(struct nl_msg *msg, int attrtype, int datalen, const void *data)
>   * @see nla_put
>   * @return 0 on success or a negative error code.
>   */
> -int nla_put_data(struct nl_msg *msg, int attrtype, struct nl_data *data)
> +int nla_put_data(struct nl_msg *msg, int attrtype, const struct nl_data *data)
>  {
>  	return nla_put(msg, attrtype, nl_data_get_size(data),
>  		       nl_data_get(data));
> @@ -571,9 +571,9 @@ int nla_put_u8(struct nl_msg *msg, int attrtype, uint8_t value)
>   *
>   * @return Payload as 8 bit integer.
>   */
> -uint8_t nla_get_u8(struct nlattr *nla)
> +uint8_t nla_get_u8(const struct nlattr *nla)
>  {
> -	return *(uint8_t *) nla_data(nla);
> +	return *(const uint8_t *) nla_data(nla);
>  }
>  
>  /**
> @@ -596,9 +596,9 @@ int nla_put_u16(struct nl_msg *msg, int attrtype, uint16_t value)
>   *
>   * @return Payload as 16 bit integer.
>   */
> -uint16_t nla_get_u16(struct nlattr *nla)
> +uint16_t nla_get_u16(const struct nlattr *nla)
>  {
> -	return *(uint16_t *) nla_data(nla);
> +	return *(const uint16_t *) nla_data(nla);
>  }
>  
>  /**
> @@ -621,9 +621,9 @@ int nla_put_u32(struct nl_msg *msg, int attrtype, uint32_t value)
>   *
>   * @return Payload as 32 bit integer.
>   */
> -uint32_t nla_get_u32(struct nlattr *nla)
> +uint32_t nla_get_u32(const struct nlattr *nla)
>  {
> -	return *(uint32_t *) nla_data(nla);
> +	return *(const uint32_t *) nla_data(nla);
>  }
>  
>  /**
> @@ -646,7 +646,7 @@ int nla_put_u64(struct nl_msg *msg, int attrtype, uint64_t value)
>   *
>   * @return Payload as 64 bit integer.
>   */
> -uint64_t nla_get_u64(struct nlattr *nla)
> +uint64_t nla_get_u64(const struct nlattr *nla)
>  {
>  	uint64_t tmp = 0;
>  
> @@ -682,12 +682,12 @@ int nla_put_string(struct nl_msg *msg, int attrtype, const char *str)
>   *
>   * @return Pointer to attribute payload.
>   */
> -char *nla_get_string(struct nlattr *nla)
> +char *nla_get_string(const struct nlattr *nla)
>  {
>  	return (char *) nla_data(nla);
>  }
>  
> -char *nla_strdup(struct nlattr *nla)
> +char *nla_strdup(const struct nlattr *nla)
>  {
>  	return strdup(nla_get_string(nla));
>  }
> @@ -717,7 +717,7 @@ int nla_put_flag(struct nl_msg *msg, int attrtype)
>   *
>   * @return True if flag is set, otherwise false.
>   */
> -int nla_get_flag(struct nlattr *nla)
> +int nla_get_flag(const struct nlattr *nla)
>  {
>  	return !!nla;
>  }
> @@ -745,7 +745,7 @@ int nla_put_msecs(struct nl_msg *n, int attrtype, unsigned long msecs)
>   *
>   * @return the number of milliseconds.
>   */
> -unsigned long nla_get_msecs(struct nlattr *nla)
> +unsigned long nla_get_msecs(const struct nlattr *nla)
>  {
>  	return nla_get_u64(nla);
>  }
> @@ -769,7 +769,8 @@ unsigned long nla_get_msecs(struct nlattr *nla)
>   * @see nla_put
>   * @return 0 on success or a negative error code.
>   */
> -int nla_put_nested(struct nl_msg *msg, int attrtype, struct nl_msg *nested)
> +int nla_put_nested(struct nl_msg *msg, int attrtype,
> +		   const struct nl_msg *nested)
>  {
>  	NL_DBG(2, "msg %p: attr <> %d: adding msg %p as nested attribute\n",
>  		msg, attrtype, nested);
> @@ -856,7 +857,7 @@ int nla_nest_end(struct nl_msg *msg, struct nlattr *start)
>   * by resetting the message to the size before the call to nla_nest_start()
>   * and by overwriting any potentially touched message segments with 0.
>   */
> -void nla_nest_cancel(struct nl_msg *msg, struct nlattr *attr)
> +void nla_nest_cancel(struct nl_msg *msg, const struct nlattr *attr)
>  {
>  	ssize_t len;
>  
> @@ -894,7 +895,7 @@ int nla_parse_nested(struct nlattr *tb[], int maxtype, struct nlattr *nla,
>   *
>   * @return True if attribute has NLA_F_NESTED flag set, oterhwise False.
>   */
> -int nla_is_nested(struct nlattr *attr)
> +int nla_is_nested(const struct nlattr *attr)
>  {
>  	return !!(attr->nla_type & NLA_F_NESTED);
>  }
> diff --git a/lib/data.c b/lib/data.c
> index 1a3a3fb..00bdb79 100644
> --- a/lib/data.c
> +++ b/lib/data.c
> @@ -47,7 +47,7 @@
>   * 
>   * @return Newly allocated data handle or NULL
>   */
> -struct nl_data *nl_data_alloc(void *buf, size_t size)
> +struct nl_data *nl_data_alloc(const void *buf, size_t size)
>  {
>  	struct nl_data *data;
>  
> @@ -81,7 +81,7 @@ errout:
>   * @see nla_data_alloc
>   * @return Newly allocated data handle or NULL
>   */
> -struct nl_data *nl_data_alloc_attr(struct nlattr *nla)
> +struct nl_data *nl_data_alloc_attr(const struct nlattr *nla)
>  {
>  	return nl_data_alloc(nla_data(nla), nla_len(nla));
>  }
> @@ -92,7 +92,7 @@ struct nl_data *nl_data_alloc_attr(struct nlattr *nla)
>   *
>   * @return Cloned object or NULL
>   */
> -struct nl_data *nl_data_clone(struct nl_data *src)
> +struct nl_data *nl_data_clone(const struct nl_data *src)
>  {
>  	return nl_data_alloc(src->d_data, src->d_size);
>  }
> @@ -108,7 +108,7 @@ struct nl_data *nl_data_clone(struct nl_data *src)
>   * 
>   * @return 0 on success or a negative error code
>   */
> -int nl_data_append(struct nl_data *data, void *buf, size_t size)
> +int nl_data_append(struct nl_data *data, const void *buf, size_t size)
>  {
>  	if (size > 0) {
>  		data->d_data = realloc(data->d_data, data->d_size + size);
> @@ -150,9 +150,11 @@ void nl_data_free(struct nl_data *data)
>   * @arg data		Abstract data object.
>   * @return Data buffer or NULL if empty.
>   */
> -void *nl_data_get(struct nl_data *data)
> +void *nl_data_get(const struct nl_data *data)
>  {
> -	return data->d_size > 0 ? data->d_data : NULL;
> +	if (data->d_size > 0)
> +		return (void*)data->d_data;
> +	return NULL;
>  }
>  
>  /**
> @@ -160,7 +162,7 @@ void *nl_data_get(struct nl_data *data)
>   * @arg data		Abstract data object.
>   * @return Size of data buffer.
>   */
> -size_t nl_data_get_size(struct nl_data *data)
> +size_t nl_data_get_size(const struct nl_data *data)
>  {
>  	return data->d_size;
>  }
> @@ -180,10 +182,10 @@ size_t nl_data_get_size(struct nl_data *data)
>   *         a is found, respectively, to be less than, to match, or
>   *         be greater than b.
>   */
> -int nl_data_cmp(struct nl_data *a, struct nl_data *b)
> +int nl_data_cmp(const struct nl_data *a, const struct nl_data *b)
>  {
> -	void *a_ = nl_data_get(a);
> -	void *b_ = nl_data_get(b);
> +	const void *a_ = nl_data_get(a);
> +	const void *b_ = nl_data_get(b);
>  
>  	if (a_ && b_)
>  		return memcmp(a_, b_, nl_data_get_size(a));