Add dnsconfig(8).

Makefile

@@ -13,6 +13,7 @@ bench \
 carray \
 checksum \
 disked \
+dnsconfig \
 editor \
 ext \
 games \

dnsconfig/.gitignore

@@ -0,0 +1 @@
+dnsconfig

dnsconfig/Makefile

@@ -0,0 +1,30 @@
+SOFTWARE_MEANT_FOR_SORTIX=1
+include ../build-aux/platform.mak
+include ../build-aux/compiler.mak
+include ../build-aux/version.mak
+include ../build-aux/dirs.mak
+
+OPTLEVEL?=$(DEFAULT_OPTLEVEL)
+CFLAGS?=$(OPTLEVEL)
+
+CFLAGS += -Wall -Wextra
+
+BINARIES = dnsconfig
+MANPAGES8 = dnsconfig.8
+
+all: $(BINARIES)
+
+.PHONY: all install clean
+
+install: all
+	mkdir -p $(DESTDIR)$(SBINDIR)
+	install $(BINARIES) $(DESTDIR)$(SBINDIR)
+	mkdir -p $(DESTDIR)$(MANDIR)/man8
+	cp $(MANPAGES8) $(DESTDIR)$(MANDIR)/man8
+
+%: %.c
+	$(CC) -std=gnu11 $(CFLAGS) $(CPPFLAGS) $< -o $@
+
+clean:
+	rm -f $(BINARIES)
+

dnsconfig/dnsconfig.8

@@ -0,0 +1,86 @@
+.Dd October 7, 2021
+.Dt DNSCONFIG 8
+.Os
+.Sh NAME
+.Nm dnsconfig
+.Nd configure kernel DNS resolver list
+.Sh SYNOPSIS
+.Nm
+.Nm
+.Ar resolver ...
+.Nm
+.Fl s
+.Op Ar resolver ...
+.Nm
+.Fl a
+.Op Ar resolver ...
+.Nm
+.Fl d
+.Op Ar resolver ...
+.Sh DESCRIPTION
+.Nm
+writes the current kernel DNS resolver list, or modifies it if any resolvers are
+specified.
+.Pp
+The options are as follows:
+.Bl -tag -width "12345678"
+.It Fl a
+Append resolvers to the list.
+.It Fl d
+Delete resolvers from the list.
+.It Fl s
+Set the resolver list.
+This option is the default if
+.Nm
+is invoked with any resolvers.
+.El
+.Sh EXIT STATUS
+.Nm
+will exit 0 on success and non-zero otherwise.
+.Sh EXAMPLES
+Get the resolvers:
+.Bd -literal
+$ dnsconfig
+192.0.2.1
+.Ed
+.Pp
+Set two resolvers:
+.Bd -literal
+# dnsconfig 192.0.2.15 192.0.2.100
+# dnsconfig
+192.0.2.15
+192.0.2.100
+.Ed
+.Pp
+Set the resolvers to the empty list:
+.Bd -literal
+# dnsconfig -s
+# dnsconfig
+.Ed
+.Pp
+Append a resolver:
+.Bd -literal
+# dnsconfig 192.0.2.128
+# dnsconfig -a 192.0.2.40
+# dnsconfig
+192.0.2.128
+192.0.2.40
+.Ed
+.Pp
+Delete a resolver:
+.Bd -literal
+# dnsconfig -d 192.0.2.128
+# dnsconfig
+192.0.2.40
+.Ed
+.Sh SEE ALSO
+.Xr getdnsconfig 2 ,
+.Xr setdnsconfig 2
+.Sh HISTORY
+.Nm
+originally appeared in Sortix 1.1.
+.Sh CAVEATS
+The kernel DNS resolver list is global state.
+Changes made with
+.Nm
+may be overwritten by other programs.

dnsconfig/dnsconfig.c

@@ -0,0 +1,130 @@
+/*
+ * Copyright (c) 2021 Juhani 'nortti' Krekelä.
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ *
+ * dnsconfig.c
+ * Configure kernel DNS resolver list.
+ */
+
+#include <sys/dnsconfig.h>
+#include <sys/socket.h>
+
+#include <arpa/inet.h>
+#include <err.h>
+#include <getopt.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <string.h>
+
+int main(int argc, char* argv[])
+{
+	bool append = false;
+	bool delete = false;
+	bool set = false;
+
+	int opt;
+	while ( (opt = getopt(argc, argv, "ads")) != -1 )
+	{
+		switch ( opt )
+		{
+		case 'a': append = true; break;
+		case 'd': delete = true; break;
+		case 's': set = true; break;
+		}
+	}
+
+	if ( append + delete + set > 1 )
+		errx(1, "-a, -d, -s are mutually exclusive");
+
+	// If no mode is provided but there are arguments, default to set.
+	if ( !append && !delete && !set && optind < argc )
+		set = true;
+
+	struct dnsconfig dnsconfig = {0};
+	if ( !set && getdnsconfig(&dnsconfig) < 0 )
+		err(1, "getdnsconfig");
+
+	if ( append || delete || set )
+	{
+		for ( int i = optind; i < argc; i++ )
+		{
+			struct dnsconfig_server server = {0};
+			if ( inet_pton(AF_INET, argv[i], &server.addr.in) )
+			{
+				server.family = AF_INET;
+				server.addrsize = sizeof(server.addr.in);
+			}
+			else if ( inet_pton(AF_INET6, argv[i], &server.addr.in6) )
+			{
+				server.family = AF_INET6;
+				server.addrsize = sizeof(server.addr.in6);
+			}
+			else
+				errx(1, "Invalid address: %s", argv[i]);
+
+			if ( !delete )
+			{
+				size_t index = dnsconfig.servers_count++;
+				if ( dnsconfig.servers_count > DNSCONFIG_MAX_SERVERS )
+					errx(1, "Too many DNS resolvers (%zu max)",
+					     (size_t) DNSCONFIG_MAX_SERVERS);
+				dnsconfig.servers[index] = server;
+			}
+			else
+			{
+				// Search for a matching entry.
+				bool found = false;
+				for ( size_t j = 0; j < dnsconfig.servers_count; j++ )
+				{
+					if ( dnsconfig.servers[j].family != server.family ||
+					     memcmp(&dnsconfig.servers[j].addr, &server.addr,
+					            server.addrsize) )
+						continue;
+
+					for ( size_t k = j + 1; k < dnsconfig.servers_count; k++ )
+						dnsconfig.servers[k - 1] = dnsconfig.servers[k];
+					dnsconfig.servers_count--;
+					memset(&dnsconfig.servers[dnsconfig.servers_count], 0,
+					       sizeof(struct dnsconfig_server));
+					found = true;
+					break;
+				}
+
+				if ( !found )
+					errx(1, "Resolver not in the list: %s", argv[i]);
+			}
+
+		}
+
+		if ( setdnsconfig(&dnsconfig) < 0 )
+			err(1, "setdnsconfig");
+	}
+	else
+	{
+		for ( size_t i = 0; i < dnsconfig.servers_count; i++ )
+		{
+			char address[INET6_ADDRSTRLEN];
+			if ( !inet_ntop(dnsconfig.servers[i].family,
+			                &dnsconfig.servers[i].addr,
+			                address, sizeof(address)) )
+				err(1, "inet_ntop");
+			if ( printf("%s\n", address) < 0 )
+				err(1, "stdout");
+		}
+		if ( fflush(stdout) )
+			err(1, "stdout");
+	}
+
+	return 0;
+}