Re: [PATCH net-next v5 1/2] net, treewide: define and use MAC_ADDR_STR_LEN

[David Laight <david.laight.linux@gmail.com>]

On Thu, 20 Feb 2025 18:29:20 -0700
Uday Shankar <ushankar@purestorage.com> wrote:

> There are a few places in the tree which compute the length of the
> string representation of a MAC address as 3 * ETH_ALEN - 1. Define a
> constant for this and use it where relevant. No functionality changes
> are expected.

The fact that you have to keep adding 1 or 2 is a good indication that
it really isn't a good idea.

	David

> 
> Signed-off-by: Uday Shankar <ushankar@purestorage.com>
> Reviewed-by: Michal Swiatkowski <michal.swiatkowski@linux.intel.com>
> Acked-by: Johannes Berg <johannes@sipsolutions.net>
> ---
>  drivers/net/netconsole.c           | 2 +-
>  drivers/nvmem/brcm_nvram.c         | 2 +-
>  drivers/nvmem/layouts/u-boot-env.c | 2 +-
>  include/linux/if_ether.h           | 3 +++
>  lib/net_utils.c                    | 4 +---
>  net/mac80211/debugfs_sta.c         | 7 ++++---
>  6 files changed, 11 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
> index f77eddf221850fe2778cd479e49c91ad695aba3c..12699831e3c9fdbafd4862a339aea4ef04cf522b 100644
> --- a/drivers/net/netconsole.c
> +++ b/drivers/net/netconsole.c
> @@ -721,7 +721,7 @@ static ssize_t remote_mac_store(struct config_item *item, const char *buf,
>  
>  	if (!mac_pton(buf, remote_mac))
>  		goto out_unlock;
> -	if (buf[3 * ETH_ALEN - 1] && buf[3 * ETH_ALEN - 1] != '\n')
> +	if (buf[MAC_ADDR_STR_LEN] && buf[MAC_ADDR_STR_LEN] != '\n')
>  		goto out_unlock;
>  	memcpy(nt->np.remote_mac, remote_mac, ETH_ALEN);
>  
> diff --git a/drivers/nvmem/brcm_nvram.c b/drivers/nvmem/brcm_nvram.c
> index b810df727b446b1762a1851750f743e0de6e8788..b4cf245fb2467d281111001bb7ed8db5993a09b2 100644
> --- a/drivers/nvmem/brcm_nvram.c
> +++ b/drivers/nvmem/brcm_nvram.c
> @@ -100,7 +100,7 @@ static int brcm_nvram_read_post_process_macaddr(void *context, const char *id, i
>  {
>  	u8 mac[ETH_ALEN];
>  
> -	if (bytes != 3 * ETH_ALEN - 1)
> +	if (bytes != MAC_ADDR_STR_LEN)
>  		return -EINVAL;
>  
>  	if (!mac_pton(buf, mac))
> diff --git a/drivers/nvmem/layouts/u-boot-env.c b/drivers/nvmem/layouts/u-boot-env.c
> index 731e6f4f12b2bf28e4547d128954a095545ad461..436426d4e8f910b51b92f88acddfbb40d374587a 100644
> --- a/drivers/nvmem/layouts/u-boot-env.c
> +++ b/drivers/nvmem/layouts/u-boot-env.c
> @@ -37,7 +37,7 @@ static int u_boot_env_read_post_process_ethaddr(void *context, const char *id, i
>  {
>  	u8 mac[ETH_ALEN];
>  
> -	if (bytes != 3 * ETH_ALEN - 1)
> +	if (bytes != MAC_ADDR_STR_LEN)
>  		return -EINVAL;
>  
>  	if (!mac_pton(buf, mac))
> diff --git a/include/linux/if_ether.h b/include/linux/if_ether.h
> index 8a9792a6427ad9cf58b50c79cbfe185615800dcb..61b7335aa037c7232a0caa45572043057c02dde3 100644
> --- a/include/linux/if_ether.h
> +++ b/include/linux/if_ether.h
> @@ -19,6 +19,9 @@
>  #include <linux/skbuff.h>
>  #include <uapi/linux/if_ether.h>
>  
> +/* XX:XX:XX:XX:XX:XX */
> +#define MAC_ADDR_STR_LEN (3 * ETH_ALEN - 1)
> +
>  static inline struct ethhdr *eth_hdr(const struct sk_buff *skb)
>  {
>  	return (struct ethhdr *)skb_mac_header(skb);
> diff --git a/lib/net_utils.c b/lib/net_utils.c
> index 42bb0473fb22f977409f7a6792bb1340f4e911c3..215cda672fee1b5a029c2b61529c6813c0edab11 100644
> --- a/lib/net_utils.c
> +++ b/lib/net_utils.c
> @@ -7,11 +7,9 @@
>  
>  bool mac_pton(const char *s, u8 *mac)
>  {
> -	size_t maxlen = 3 * ETH_ALEN - 1;
>  	int i;
>  
> -	/* XX:XX:XX:XX:XX:XX */
> -	if (strnlen(s, maxlen) < maxlen)
> +	if (strnlen(s, MAC_ADDR_STR_LEN) < MAC_ADDR_STR_LEN)
>  		return false;
>  
>  	/* Don't dirty result unless string is valid MAC. */
> diff --git a/net/mac80211/debugfs_sta.c b/net/mac80211/debugfs_sta.c
> index a67a9d3160086ac492d77092a0c8a74d2384b28c..a8948f4d983e5edee45d90ad267582657ed38e38 100644
> --- a/net/mac80211/debugfs_sta.c
> +++ b/net/mac80211/debugfs_sta.c
> @@ -457,11 +457,12 @@ static ssize_t link_sta_addr_read(struct file *file, char __user *userbuf,
>  				  size_t count, loff_t *ppos)
>  {
>  	struct link_sta_info *link_sta = file->private_data;
> -	u8 mac[3 * ETH_ALEN + 1];
> +	u8 mac[MAC_ADDR_STR_LEN + 2];
>  
>  	snprintf(mac, sizeof(mac), "%pM\n", link_sta->pub->addr);
>  
> -	return simple_read_from_buffer(userbuf, count, ppos, mac, 3 * ETH_ALEN);
> +	return simple_read_from_buffer(userbuf, count, ppos, mac,
> +				       MAC_ADDR_STR_LEN + 1);
>  }
>  
>  LINK_STA_OPS(addr);
> @@ -1240,7 +1241,7 @@ void ieee80211_sta_debugfs_add(struct sta_info *sta)
>  	struct ieee80211_local *local = sta->local;
>  	struct ieee80211_sub_if_data *sdata = sta->sdata;
>  	struct dentry *stations_dir = sta->sdata->debugfs.subdir_stations;
> -	u8 mac[3*ETH_ALEN];
> +	u8 mac[MAC_ADDR_STR_LEN + 1];
>  
>  	if (!stations_dir)
>  		return;
>