netdev - Re: [PATCH net-next 1/2] lib: vsprintf: add IPv4/v6 generic %pig/%pIg format specifier

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Date:	Wed, 26 Jun 2013 13:27:19 -0400
From:	Vlad Yasevich <vyasevich@...il.com>
To:	Daniel Borkmann <dborkman@...hat.com>
CC:	davem@...emloft.net, netdev@...r.kernel.org,
	linux-sctp@...r.kernel.org
Subject: Re: [PATCH net-next 1/2] lib: vsprintf: add IPv4/v6 generic %pig/%pIg
 format specifier

On 06/26/2013 01:01 PM, Daniel Borkmann wrote:
> In order to avoid making code that deals with printing both, IPv4 and
> IPv6 addresses, unnecessary complicated as for example ...
>
>    if (sa.sa_family == AF_INET6)
>      printk("... %pI6 ...", sin6_addr);
>    else
>      printk("... %pI4 ...", sin_addr.s_addr);
>
> ... it would be better to introduce a format specifier that can deal
> with those kind of situations internally; just as we have a "struct
> sockaddr" for generic mapping into "struct sockaddr_in" or "struct
> sockaddr_in6" as e.g. done in "union sctp_addr". Then, we could
> reduce the above statement into something like:
>
>    printk("... %pIg ..", &sockaddr);
>
> While we're at it, support for both %pig/%pIg, where 'g' stands for
> generic, comes for free. In case our pointer is NULL, pointer() then
> deals with that already at an earlier point in time internally.
>
> Likely, there are many other areas than just SCTP in the kernel to make
> use of this extension as well.
>
> Signed-off-by: Daniel Borkmann <dborkman@...hat.com>
> ---
>   lib/vsprintf.c | 18 ++++++++++++++++--
>   1 file changed, 16 insertions(+), 2 deletions(-)

I think you should also update Documentation/printk-formats.txt

-vlad

>
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index e149c64..7243742 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -1004,10 +1004,10 @@ int kptr_restrict __read_mostly;
>    * - 'MF' For a 6-byte MAC FDDI address, it prints the address
>    *       with a dash-separated hex notation
>    * - '[mM]R' For a 6-byte MAC address, Reverse order (Bluetooth)
> - * - 'I' [46] for IPv4/IPv6 addresses printed in the usual way
> + * - 'I' [46g] for IPv4/IPv6 addresses printed in the usual way
>    *       IPv4 uses dot-separated decimal without leading 0's (1.2.3.4)
>    *       IPv6 uses colon separated network-order 16 bit hex with leading 0's
> - * - 'i' [46] for 'raw' IPv4/IPv6 addresses
> + * - 'i' [46g] for 'raw' IPv4/IPv6 addresses
>    *       IPv6 omits the colons (01020304...0f)
>    *       IPv4 uses dot-separated decimal with leading 0's (010.123.045.006)
>    * - '[Ii]4[hnbl]' IPv4 addresses in host, network, big or little endian order
> @@ -1093,6 +1093,18 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
>   			return ip6_addr_string(buf, end, ptr, spec, fmt);
>   		case '4':
>   			return ip4_addr_string(buf, end, ptr, spec, fmt);
> +		case 'g':
> +			{
> +				const struct sockaddr *sa = ptr;
> +
> +				if (sa->sa_family == AF_INET6) {
> +					ptr = &((struct sockaddr_in6 *) sa)->sin6_addr;
> +					return ip6_addr_string(buf, end, ptr, spec, fmt);
> +				} else {
> +					ptr = &((struct sockaddr_in *) sa)->sin_addr.s_addr;
> +					return ip4_addr_string(buf, end, ptr, spec, fmt);
> +				}
> +			}
>   		}
>   		break;
>   	case 'U':
> @@ -1370,6 +1382,8 @@ qualifier:
>    * %pI6 print an IPv6 address with colons
>    * %pi6 print an IPv6 address without colons
>    * %pI6c print an IPv6 address as specified by RFC 5952
> + * %pIg depending on sa_family of 'struct sockaddr *' switch to %pI6/%pI4
> + * %pig depending on sa_family of 'struct sockaddr *' switch to %pi6/%pi4
>    * %pU[bBlL] print a UUID/GUID in big or little endian using lower or upper
>    *   case.
>    * %*ph[CDN] a variable-length hex string with a separator (supports up to 64
>

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