dnsd: add -s option. This allows (clumsy) operation with read dns servers

function                                             old     new   delta
packed_usage                                       26816   26886     +70
dnsd_main                                           1299    1303      +4

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

2 files changed, 45 insertions, 35 deletions

diff --git a/include/usage.h b/include/usage.h
index 109a35d05..c2ffb6d6e 100644
--- a/include/usage.h
+++ b/include/usage.h
@@ -893,7 +893,7 @@
      "\n        -s SIZE         Buffer size" \
 
 #define dnsd_trivial_usage \
-       "[-c CONFFILE] [-t TTL_SEC] [-p PORT] [-i ADDR] [-d]"
+       "[-dvs] [-c CONFFILE] [-t TTL_SEC] [-p PORT] [-i ADDR]"
 #define dnsd_full_usage "\n\n" \
        "Small static DNS server daemon\n" \
      "\nOptions:" \
@@ -902,6 +902,11 @@
      "\n        -p PORT Listen on PORT" \
      "\n        -i ADDR Listen on ADDR" \
      "\n        -d      Daemonize" \
+     "\n        -v      Verbose" \
+     "\n        -s      Send successful replies only. Use this if you want" \
+     "\n                to use /etc/resolv.conf with two nameserver lines:" \
+     "\n                        nameserver DNSD_SERVER" \
+     "\n                        nameserver NORNAL_DNS_SERVER" \
 
 #define dos2unix_trivial_usage \
        "[OPTIONS] [FILE]"
diff --git a/networking/dnsd.c b/networking/dnsd.c
index 42deb1f35..e73e244b0 100644
--- a/networking/dnsd.c
+++ b/networking/dnsd.c
@@ -56,7 +56,8 @@ struct dns_entry {
         char name[1];
 };
 
-#define OPT_verbose (option_mask32)
+#define OPT_verbose (option_mask32 & 1)
+#define OPT_silent  (option_mask32 & 2)
 
 
 /*
@@ -351,10 +352,11 @@ static int process_packet(struct dns_entry *conf_data,
                 uint32_t conf_ttl,
                 uint8_t *buf)
 {
-        char *answstr;
         struct dns_head *head;
         struct type_and_class *unaligned_type_class;
+        const char *err_msg;
         char *query_string;
+        char *answstr;
         uint8_t *answb;
         uint16_t outr_rlen;
         uint16_t outr_flags;
@@ -365,12 +367,19 @@ static int process_packet(struct dns_entry *conf_data,
         head = (struct dns_head *)buf;
         if (head->nquer == 0) {
                 bb_error_msg("packet has 0 queries, ignored");
-                return -1;
+                return 0; /* don't reply */
         }
-
         if (head->flags & htons(0x8000)) { /* QR bit */
                 bb_error_msg("response packet, ignored");
-                return -1;
+                return 0; /* don't reply */
+        }
+        /* QR = 1 "response", RCODE = 4 "Not Implemented" */
+        outr_flags = htons(0x8000 | 4);
+        err_msg = NULL;
+        /* OPCODE != 0 "standard query" ? */
+        if ((head->flags & htons(0x7800)) != 0) {
+                err_msg = "opcode != 0";
+                goto empty_packet;
         }
 
         /* start of query string */
@@ -383,28 +392,16 @@ static int process_packet(struct dns_entry *conf_data,
         /* where to append answer block */
         answb = (void *)(unaligned_type_class + 1);
 
-        /* QR = 1 "response", RCODE = 4 "Not Implemented" */
-        outr_flags = htons(0x8000 | 4);
-
-        move_from_unaligned16(type, &unaligned_type_class->type);
-        if (type != htons(REQ_A) && type != htons(REQ_PTR)) {
-                /* we can't handle this query type */
-//TODO: handle REQ_AAAA (0x1c) requests
-                bb_error_msg("type %u is !REQ_A and !REQ_PTR%s",
-                                (int)ntohs(type),
-                                ", returning Not Implemented reply");
-                goto empty_packet;
-        }
         move_from_unaligned16(class, &unaligned_type_class->class);
         if (class != htons(1)) { /* not class INET? */
-                bb_error_msg("class != 1%s",
-                                ", returning Not Implemented reply");
+                err_msg = "class != 1";
                 goto empty_packet;
         }
-        /* OPCODE != 0 "standard query" ? */
-        if ((head->flags & htons(0x7800)) != 0) {
-                bb_error_msg("opcode != 0%s",
-                                ", returning Not Implemented reply");
+        move_from_unaligned16(type, &unaligned_type_class->type);
+        if (type != htons(REQ_A) && type != htons(REQ_PTR)) {
+                /* we can't handle this query type */
+//TODO: happens all the time with REQ_AAAA (0x1c) requests - implement those?
+                err_msg = "type is !REQ_A and !REQ_PTR";
                 goto empty_packet;
         }
 
@@ -425,8 +422,7 @@ static int process_packet(struct dns_entry *conf_data,
                 /* QR = 1 "response"
                  * AA = 1 "Authoritative Answer"
                  * RCODE = 3 "Name Error" */
-                if (OPT_verbose)
-                        bb_error_msg("returning Name Error reply");
+                err_msg = "name is not found";
                 outr_flags = htons(0x8000 | 0x0400 | 3);
                 goto empty_packet;
         }
@@ -455,6 +451,16 @@ static int process_packet(struct dns_entry *conf_data,
         head->nansw = htons(1);
 
  empty_packet:
+        if ((outr_flags & htons(0xf)) != 0) { /* not a positive response */
+                if (OPT_verbose) {
+                        bb_error_msg("%s, %s",
+                                err_msg,
+                                OPT_silent ? "dropping query" : "sending error reply"
+                        );
+                }
+                if (OPT_silent)
+                        return 0;
+        }
         head->flags |= outr_flags;
         head->nauth = head->nadd = 0;
         head->nquer = htons(1); // why???
@@ -476,21 +482,20 @@ int dnsd_main(int argc UNUSED_PARAM, char **argv)
         uint16_t port = 53;
         uint8_t buf[MAX_PACK_LEN + 1];
 
-        opts = getopt32(argv, "vi:c:t:p:d", &listen_interface, &fileconf, &sttl, &sport);
-        //if (opts & 0x1) // -v
-        //if (opts & 0x2) // -i
-        //if (opts & 0x4) // -c
-        if (opts & 0x8) // -t
+        opts = getopt32(argv, "vsi:c:t:p:d", &listen_interface, &fileconf, &sttl, &sport);
+        //if (opts & (1 << 0)) // -v
+        //if (opts & (1 << 1)) // -s
+        //if (opts & (1 << 2)) // -i
+        //if (opts & (1 << 3)) // -c
+        if (opts & (1 << 4)) // -t
                 conf_ttl = xatou_range(sttl, 1, 0xffffffff);
-        if (opts & 0x10) // -p
+        if (opts & (1 << 5)) // -p
                 port = xatou_range(sport, 1, 0xffff);
-        if (opts & 0x20) { // -d
+        if (opts & (1 << 6)) { // -d
                 bb_daemonize_or_rexec(DAEMON_CLOSE_EXTRA_FDS, argv);
                 openlog(applet_name, LOG_PID, LOG_DAEMON);
                 logmode = LOGMODE_SYSLOG;
         }
-        /* Clear all except "verbose" bit */
-        option_mask32 &= 1;
 
         conf_data = parse_conf_file(fileconf);