devip: add support for IPv6

Addresses are now stored as uchar[16] instead
of ulong, with enough room for IPv6.

Generic IP functions have been removed from
devip.c and replaced by libip, imported from
Plan 9.

Names and addresses are resolved using either
gethostbyname() or getaddrinfo() functions.

On Windows, IPv6 name resolution is not enabled,
because mingw32 doesn't provide inet_ntop().

R=rsc
http://codereview.appspot.com/6408044

libip/eipfmt.c

@@ -0,0 +1,109 @@
+#include <u.h>
+#include <libc.h>
+#include <ip.h>
+
+enum
+{
+	Isprefix= 16,
+};
+
+uchar prefixvals[256] =
+{
+[0x00] 0 | Isprefix,
+[0x80] 1 | Isprefix,
+[0xC0] 2 | Isprefix,
+[0xE0] 3 | Isprefix,
+[0xF0] 4 | Isprefix,
+[0xF8] 5 | Isprefix,
+[0xFC] 6 | Isprefix,
+[0xFE] 7 | Isprefix,
+[0xFF] 8 | Isprefix,
+};
+
+int
+eipfmt(Fmt *f)
+{
+	char buf[5*8];
+	static char *efmt = "%.2ux%.2ux%.2ux%.2ux%.2ux%.2ux";
+	static char *ifmt = "%d.%d.%d.%d";
+	uchar *p, ip[16];
+	ulong *lp;
+	ushort s;
+	int i, j, n, eln, eli;
+
+	switch(f->r) {
+	case 'E':		/* Ethernet address */
+		p = va_arg(f->args, uchar*);
+		snprint(buf, sizeof buf, efmt, p[0], p[1], p[2], p[3], p[4], p[5]);
+		return fmtstrcpy(f, buf);
+
+	case 'I':		/* Ip address */
+		p = va_arg(f->args, uchar*);
+common:
+		if(memcmp(p, v4prefix, 12) == 0){
+			snprint(buf, sizeof buf, ifmt, p[12], p[13], p[14], p[15]);
+			return fmtstrcpy(f, buf);
+		}
+
+		/* find longest elision */
+		eln = eli = -1;
+		for(i = 0; i < 16; i += 2){
+			for(j = i; j < 16; j += 2)
+				if(p[j] != 0 || p[j+1] != 0)
+					break;
+			if(j > i && j - i > eln){
+				eli = i;
+				eln = j - i;
+			}
+		}
+
+		/* print with possible elision */
+		n = 0;
+		for(i = 0; i < 16; i += 2){
+			if(i == eli){
+				n += sprint(buf+n, "::");
+				i += eln;
+				if(i >= 16)
+					break;
+			} else if(i != 0)
+				n += sprint(buf+n, ":");
+			s = (p[i]<<8) + p[i+1];
+			n += sprint(buf+n, "%ux", s);
+		}
+		return fmtstrcpy(f, buf);
+
+	case 'i':		/* v6 address as 4 longs */
+		lp = va_arg(f->args, ulong*);
+		for(i = 0; i < 4; i++)
+			hnputl(ip+4*i, *lp++);
+		p = ip;
+		goto common;
+
+	case 'V':		/* v4 ip address */
+		p = va_arg(f->args, uchar*);
+		snprint(buf, sizeof buf, ifmt, p[0], p[1], p[2], p[3]);
+		return fmtstrcpy(f, buf);
+
+	case 'M':		/* ip mask */
+		p = va_arg(f->args, uchar*);
+
+		/* look for a prefix mask */
+		for(i = 0; i < 16; i++)
+			if(p[i] != 0xff)
+				break;
+		if(i < 16){
+			if((prefixvals[p[i]] & Isprefix) == 0)
+				goto common;
+			for(j = i+1; j < 16; j++)
+				if(p[j] != 0)
+					goto common;
+			n = 8*i + (prefixvals[p[i]] & ~Isprefix);
+		} else
+			n = 8*16;
+
+		/* got one, use /xx format */
+		snprint(buf, sizeof buf, "/%d", n);
+		return fmtstrcpy(f, buf);
+	}
+	return fmtstrcpy(f, "(eipfmt)");
+}