lib: vsprintf: add IPv4/v6 generic %p[Ii]S[pfs] format specifier

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("... %pIS ..", &sockaddr);

In case our pointer is NULL, pointer() then deals with that already at
an earlier point in time internally. While we're at it, support for both
%piS/%pIS, where 'S' stands for sockaddr, comes (almost) for free.

Additionally to that, postfix specifiers 'p', 'f' and 's' are supported
as suggested and initially implemented in 2009 by Joe Perches [1].
Handling of those additional specifiers orientate on the initial RFC that
was proposed. Also we support IPv6 compressed format specified by 'c' and
various other IPv4 extensions as stated in the documentation part.

Likely, there are many other areas than just SCTP in the kernel to make
use of this extension as well.

 [1] http://patchwork.ozlabs.org/patch/31480/

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
CC: Joe Perches <joe@perches.com>
CC: linux-kernel@vger.kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 32 insertions, 0 deletions

diff --git a/Documentation/printk-formats.txt b/Documentation/printk-formats.txt
index 3af5ae6c9c11..3e8cb73ac43c 100644
--- a/Documentation/printk-formats.txt
+++ b/Documentation/printk-formats.txt
@@ -121,6 +121,38 @@ IPv6 addresses:
 	print a compressed IPv6 address as described by
 	http://tools.ietf.org/html/rfc5952
 
+IPv4/IPv6 addresses (generic, with port, flowinfo, scope):
+
+	%pIS	1.2.3.4		or 0001:0002:0003:0004:0005:0006:0007:0008
+	%piS	001.002.003.004	or 00010002000300040005000600070008
+	%pISc	1.2.3.4		or 1:2:3:4:5:6:7:8
+	%pISpc	1.2.3.4:12345	or [1:2:3:4:5:6:7:8]:12345
+	%p[Ii]S[pfschnbl]
+
+	For printing an IP address without the need to distinguish whether it's
+	of type AF_INET or AF_INET6, a pointer to a valid 'struct sockaddr',
+	specified through 'IS' or 'iS', can be passed to this format specifier.
+
+	The additional 'p', 'f', and 's' specifiers are used to specify port
+	(IPv4, IPv6), flowinfo (IPv6) and scope (IPv6). Ports have a ':' prefix,
+	flowinfo a '/' and scope a '%', each followed by the actual value.
+
+	In case of an IPv6 address the compressed IPv6 address as described by
+	http://tools.ietf.org/html/rfc5952 is being used if the additional
+	specifier 'c' is given. The IPv6 address is surrounded by '[', ']' in
+	case of additional specifiers 'p', 'f' or 's' as suggested by
+	https://tools.ietf.org/html/draft-ietf-6man-text-addr-representation-07
+
+	In case of IPv4 addresses, the additional 'h', 'n', 'b', and 'l'
+	specifiers can be used as well and are ignored in case of an IPv6
+	address.
+
+	Further examples:
+
+	%pISfc		1.2.3.4		or [1:2:3:4:5:6:7:8]/123456789
+	%pISsc		1.2.3.4		or [1:2:3:4:5:6:7:8]%1234567890
+	%pISpfc		1.2.3.4:12345	or [1:2:3:4:5:6:7:8]:12345/123456789
+
 UUID/GUID addresses:
 
 	%pUb	00010203-0405-0607-0809-0a0b0c0d0e0f