[PATCH v3] vsprintf: automatic parameters for %pIS via 'a'

["Jason A. Donenfeld" <Jason@zx2c4.com>]

This patch adds a variable 'a' which indicates that the 'p',
'f', and 's' options should be toggled on or off depending on
whether or not those parameters are actually valid inside the
passed sockaddr.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 Documentation/printk-formats.txt |  6 ++++--
 lib/vsprintf.c                   | 19 +++++++++++++++++--
 2 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/Documentation/printk-formats.txt b/Documentation/printk-formats.txt
index 5d1128b..22bae97 100644
--- a/Documentation/printk-formats.txt
+++ b/Documentation/printk-formats.txt
@@ -193,7 +193,7 @@ IPv4/IPv6 addresses (generic, with port, flowinfo, scope):
 	%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]
+	%p[Ii]S[pfsachnbl]
 
 	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',
@@ -201,7 +201,9 @@ IPv4/IPv6 addresses (generic, with port, flowinfo, scope):
 
 	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.
+	flowinfo a '/' and scope a '%', each followed by the actual value. If 'a'
+	is given, 'p', 'f', and 's' are activated or deactivated depending on
+	whether or not the sockaddr has a non-zero port, flowinfo, and scope.
 
 	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
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 48ff9c3..cda27b4 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -1145,7 +1145,7 @@ static noinline_for_stack
 char *ip6_addr_string_sa(char *buf, char *end, const struct sockaddr_in6 *sa,
 			 struct printf_spec spec, const char *fmt)
 {
-	bool have_p = false, have_s = false, have_f = false, have_c = false;
+	bool have_p = false, have_s = false, have_f = false, have_c = false, have_a = false;
 	char ip6_addr[sizeof("[xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:255.255.255.255]") +
 		      sizeof(":12345") + sizeof("/123456789") +
 		      sizeof("%1234567890")];
@@ -1169,9 +1169,18 @@ char *ip6_addr_string_sa(char *buf, char *end, const struct sockaddr_in6 *sa,
 		case 'c':
 			have_c = true;
 			break;
+		case 'a':
+			have_a = true;
+			break;
 		}
 	}
 
+	if (have_a) {
+		have_p = sa->sin6_port;
+		have_s = sa->sin6_scope_id;
+		have_f = sa->sin6_flowinfo & IPV6_FLOWINFO_MASK;
+	}
+
 	if (have_p || have_s || have_f) {
 		*p = '[';
 		off = 1;
@@ -1207,7 +1216,7 @@ static noinline_for_stack
 char *ip4_addr_string_sa(char *buf, char *end, const struct sockaddr_in *sa,
 			 struct printf_spec spec, const char *fmt)
 {
-	bool have_p = false;
+	bool have_p = false, have_a = false;
 	char *p, ip4_addr[sizeof("255.255.255.255") + sizeof(":12345")];
 	char *pend = ip4_addr + sizeof(ip4_addr);
 	const u8 *addr = (const u8 *) &sa->sin_addr.s_addr;
@@ -1225,9 +1234,15 @@ char *ip4_addr_string_sa(char *buf, char *end, const struct sockaddr_in *sa,
 		case 'b':
 			fmt4[2] = *fmt;
 			break;
+		case 'a':
+			have_a = true;
+			break;
 		}
 	}
 
+	if (have_a)
+		have_p = sa->sin_port;
+
 	p = ip4_string(ip4_addr, addr, fmt4);
 	if (have_p) {
 		*p++ = ':';
-- 
2.7.0