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

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Date:	Thu, 27 Jun 2013 07:00:23 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	Vlad Yasevich <vyasevich@...il.com>
Cc:	Daniel Borkmann <dborkman@...hat.com>, 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 Wed, Jun 26, 2013 at 01:27:19PM -0400, Vlad Yasevich wrote:
> 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
> 
Just FYI, Cong Wang just posted a patch series to netdev to make generic
printing of addresses possible
http://marc.info/?l=linux-netdev&m=137231556918786&w=2
Neil

> >
> >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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