[DTrace-devel] [PATCH] Avoid "::" in inet_ntoa6 output if no zero-words are collapsed

[eugene.loh at oracle.com]

From: Eugene Loh <eugene.loh at oracle.com>

The case of no zero-words to collapse is the most common case in the
lookup table!  (Entry 0x70 accounts for over 20% of the entries.)

Signed-off-by: Eugene Loh <eugene.loh at oracle.com>
---
 bpf/inet_ntoa6.S                              |  9 +++++++++
 .../funcs/inet_ntoa6/tst.inet_ntoa6.d         | 20 +++++++++++++++++++
 .../funcs/inet_ntoa6/tst.inet_ntoa6.r         |  1 +
 .../inet_ntoa6/tst.inet_ntoa6.strsize_40.r    |  2 +-
 4 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/bpf/inet_ntoa6.S b/bpf/inet_ntoa6.S
index a4f56da8..7e4e284f 100644
--- a/bpf/inet_ntoa6.S
+++ b/bpf/inet_ntoa6.S
@@ -286,6 +286,15 @@ dt_inet_ntoa6:
 	add	%r1, %r0		/* #(words used) */
 	jgt	%r1, 8, .Ldone
 
+	/*
+	 * Special case:  if there are no collapsed zero-words, then the
+	 * "::" should not appear.  Back the output up 1 byte, so that
+	 * the two ':' will overwrite one another.
+	 */
+	jne	%r0, 0, .Lnorm
+	add	%r9, -1
+.Lnorm:
+
 	/*
 	 * Calculate the number of words left to output, and advance the input
 	 * pointer to the start of the remaining words.
diff --git a/test/unittest/funcs/inet_ntoa6/tst.inet_ntoa6.d b/test/unittest/funcs/inet_ntoa6/tst.inet_ntoa6.d
index 1f316afb..8eea1346 100644
--- a/test/unittest/funcs/inet_ntoa6/tst.inet_ntoa6.d
+++ b/test/unittest/funcs/inet_ntoa6/tst.inet_ntoa6.d
@@ -14,6 +14,7 @@ struct in6_addr *ip6d;
 struct in6_addr *ip6e;
 struct in6_addr *ip6f;
 struct in6_addr *ip6g;
+struct in6_addr *ip6h;
 
 BEGIN
 {
@@ -24,6 +25,7 @@ BEGIN
 	this->buf6e = alloca(sizeof(struct in6_addr));
 	this->buf6f = alloca(sizeof(struct in6_addr));
 	this->buf6g = alloca(sizeof(struct in6_addr));
+	this->buf6h = alloca(sizeof(struct in6_addr));
 	ip6a = this->buf6a;
 	ip6b = this->buf6b;
 	ip6c = this->buf6c;
@@ -31,6 +33,7 @@ BEGIN
 	ip6e = this->buf6e;
 	ip6f = this->buf6f;
 	ip6g = this->buf6g;
+	ip6h = this->buf6h;
 
 	ip6a->in6_u.u6_addr8[0] = 0xfe;
 	ip6a->in6_u.u6_addr8[1] = 0x80;
@@ -61,6 +64,22 @@ BEGIN
 	ip6g->in6_u.u6_addr8[11] = 0xfe;
 	ip6g->in6_u.u6_addr8[12] = 0x7f;
 	ip6g->in6_u.u6_addr8[15] = 0x01;
+	ip6h->in6_u.u6_addr8[0] = 0xff;
+	ip6h->in6_u.u6_addr8[1] = 0xff;
+	ip6h->in6_u.u6_addr8[2] = 0xff;
+	ip6h->in6_u.u6_addr8[3] = 0xff;
+	ip6h->in6_u.u6_addr8[4] = 0xff;
+	ip6h->in6_u.u6_addr8[5] = 0xff;
+	ip6h->in6_u.u6_addr8[6] = 0xff;
+	ip6h->in6_u.u6_addr8[7] = 0xff;
+	ip6h->in6_u.u6_addr8[8] = 0xff;
+	ip6h->in6_u.u6_addr8[9] = 0xff;
+	ip6h->in6_u.u6_addr8[10] = 0xff;
+	ip6h->in6_u.u6_addr8[11] = 0xff;
+	ip6h->in6_u.u6_addr8[12] = 0xff;
+	ip6h->in6_u.u6_addr8[13] = 0xff;
+	ip6h->in6_u.u6_addr8[14] = 0xff;
+	ip6h->in6_u.u6_addr8[15] = 0xff;
 
 	printf("%s\n", inet_ntoa6(ip6a));
 	printf("%s\n", inet_ntoa6(ip6b));
@@ -69,6 +88,7 @@ BEGIN
 	printf("%s\n", inet_ntoa6(ip6e));
 	printf("%s\n", inet_ntoa6(ip6f));
 	printf("%s\n", inet_ntoa6(ip6g));
+	printf("%s\n", inet_ntoa6(ip6h));
 
 	exit(0);
 }
diff --git a/test/unittest/funcs/inet_ntoa6/tst.inet_ntoa6.r b/test/unittest/funcs/inet_ntoa6/tst.inet_ntoa6.r
index d87c1f61..c3cebd6d 100644
--- a/test/unittest/funcs/inet_ntoa6/tst.inet_ntoa6.r
+++ b/test/unittest/funcs/inet_ntoa6/tst.inet_ntoa6.r
@@ -5,4 +5,5 @@ fe80::214:4fff:fe0b:76c8
 127.0.0.1
 127.0.0.1
 ::fffe:7f00:1
+ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff
 
diff --git a/test/unittest/funcs/inet_ntoa6/tst.inet_ntoa6.strsize_40.r b/test/unittest/funcs/inet_ntoa6/tst.inet_ntoa6.strsize_40.r
index 3320cd34..cef7a61a 100644
--- a/test/unittest/funcs/inet_ntoa6/tst.inet_ntoa6.strsize_40.r
+++ b/test/unittest/funcs/inet_ntoa6/tst.inet_ntoa6.strsize_40.r
@@ -1,4 +1,4 @@
-fe80:7060:5040:3080:3214:4fff:fe0b::76c8
+fe80:7060:5040:3080:3214:4fff:fe0b:76c8
 1080::808:c:417a
 ::1
 ::
-- 
2.18.4