Use a socketpair rather than a pair of pipes for communication between

ndhc and ifch, similar to sockd.  A single pipe is also maintained so
that SIGPIPE can bound the lifetime of an orphaned ifch process.

src/ifchange.c

@@ -187,7 +187,7 @@ static int ifchd_cmd(char *b, size_t bl, uint8_t *od, ssize_t ol, uint8_t code)
 static void pipewrite(struct client_state_t *cs, const char *buf, size_t count)
 {
     cs->ifchWorking = 1;
-    ssize_t r = safe_write(pToIfchW, buf, count);
+    ssize_t r = safe_write(ifchSock[0], buf, count);
     if (r < 0 || (size_t)r != count) {
         log_error("%s: (%s) write failed: %d", client_config.interface);
         return;

src/ifchd.c

@@ -307,7 +307,7 @@ static void signal_dispatch(void)
 
 static void inform_execute(char c)
 {
-    ssize_t r = safe_write(pToNdhcW, &c, sizeof c);
+    ssize_t r = safe_write(ifchSock[1], &c, sizeof c);
     if (r == 0) {
         // Remote end hung up.
         exit(EXIT_SUCCESS);
@@ -321,7 +321,7 @@ static void process_client_pipe(void)
     char buf[MAX_BUF];
 
     memset(buf, '\0', sizeof buf);
-    ssize_t r = safe_read(pToIfchR, buf, sizeof buf - 1);
+    ssize_t r = safe_recv(ifchSock[1], buf, sizeof buf - 1, MSG_DONTWAIT);
     if (r == 0) {
         // Remote end hung up.
         exit(EXIT_SUCCESS);
@@ -354,7 +354,7 @@ static void do_ifch_work(void)
     memset(cl.namesvrs, 0, sizeof cl.namesvrs);
     memset(cl.domains, 0, sizeof cl.domains);
 
-    epoll_add(epollfd, pToIfchR);
+    epoll_add(epollfd, ifchSock[1]);
     epoll_add(epollfd, signalFd);
 
     for (;;) {
@@ -367,7 +367,7 @@ static void do_ifch_work(void)
         }
         for (int i = 0; i < r; ++i) {
             int fd = events[i].data.fd;
-            if (fd == pToIfchR)
+            if (fd == ifchSock[1])
                 process_client_pipe();
             else if (fd == signalFd)
                 signal_dispatch();

src/ndhc.c

@@ -241,7 +241,7 @@ static void fail_if_state_dir_dne(void)
 static void handle_ifch_message(void)
 {
     char c;
-    ssize_t r = safe_read(pToNdhcR, &c, sizeof c);
+    ssize_t r = safe_recv(ifchSock[0], &c, sizeof c, MSG_DONTWAIT);
     if (r == 0) {
         // Remote end hung up.
         exit(EXIT_SUCCESS);
@@ -273,7 +273,7 @@ static void do_ndhc_work(void)
     setup_signals_ndhc();
 
     epoll_add(cs.epollFd, cs.nlFd);
-    epoll_add(cs.epollFd, pToNdhcR);
+    epoll_add(cs.epollFd, ifchSock[0]);
     set_listen_raw(&cs);
     nowts = curms();
     goto jumpstart;
@@ -296,7 +296,7 @@ static void do_ndhc_work(void)
                 handle_arp_response(&cs);
             else if (fd == cs.nlFd)
                 handle_nl_message(&cs);
-            else if (fd == pToNdhcR)
+            else if (fd == ifchSock[0])
                 handle_ifch_message();
             else
                 suicide("epoll_wait: unknown fd");
@@ -336,39 +336,20 @@ char resolv_conf_d[PATH_MAX] = "";
 static char pidfile[PATH_MAX] = PID_FILE_DEFAULT;
 static uid_t ndhc_uid = 0;
 static gid_t ndhc_gid = 0;
-
-int pToNdhcR;
-int pToNdhcW;
-int pToIfchR;
-int pToIfchW;
-
+int ifchSock[2];
+int ifchPipe[2];
 int sockdSock[2];
 int sockdPipe[2];
 
 static void create_ifch_ipc_pipes(void) {
-    int niPipe[2];
-    int inPipe[2];
-
-    if (pipe2(niPipe, 0))
-        suicide("FATAL - can't create ndhc -> ndhc-ifch pipe: %s",
-                strerror(errno));
-    if (fcntl(niPipe[0], F_SETFL, fcntl(niPipe[0], F_GETFL) | O_NONBLOCK) < 0)
-        suicide("FATAL - failed to set ndhc -> ndhc-ifch read-side nonblocking: %s",
-                strerror(errno));
-    pToNdhcR = niPipe[0];
-    pToNdhcW = niPipe[1];
-    if (pipe2(inPipe, 0))
-        suicide("FATAL - can't create ndhc-ifch -> ndhc pipe: %s",
-                strerror(errno));
-    if (fcntl(inPipe[0], F_SETFL, fcntl(inPipe[0], F_GETFL) | O_NONBLOCK) < 0)
-        suicide("FATAL - failed to set ndhc-ifch -> ndhc read-side nonblocking: %s",
-                strerror(errno));
-    pToIfchR = inPipe[0];
-    pToIfchW = inPipe[1];
+    if (pipe(ifchPipe))
+        suicide("FATAL - can't create ndhc/ifch pipe: %s", strerror(errno));
+    if (socketpair(AF_UNIX, SOCK_DGRAM, 0, ifchSock) < 0)
+        suicide("FATAL - can't create ndhc/ifch socket: %s", strerror(errno));
 }
 
 static void create_sockd_ipc_pipes(void) {
-    if (pipe2(sockdPipe, 0))
+    if (pipe(sockdPipe))
         suicide("FATAL - can't create ndhc/sockd pipe: %s", strerror(errno));
     if (socketpair(AF_UNIX, SOCK_DGRAM, 0, sockdSock) < 0)
         suicide("FATAL - can't create ndhc/sockd socket: %s", strerror(errno));
@@ -379,14 +360,14 @@ static void spawn_ifch(void)
     create_ifch_ipc_pipes();
     pid_t ifch_pid = fork();
     if (ifch_pid == 0) {
-        close(pToNdhcR);
-        close(pToIfchW);
+        close(ifchSock[0]);
+        close(ifchPipe[0]);
         // Don't share the RNG state with the master process.
         nk_random_u32_init(&cs.rnd32_state);
         ifch_main();
     } else if (ifch_pid > 0) {
-        close(pToIfchR);
-        close(pToNdhcW);
+        close(ifchSock[1]);
+        close(ifchPipe[1]);
     } else
         suicide("failed to fork ndhc-ifch: %s", strerror(errno));
 }
@@ -396,8 +377,8 @@ static void spawn_sockd(void)
     create_sockd_ipc_pipes();
     pid_t sockd_pid = fork();
     if (sockd_pid == 0) {
-        close(sockdPipe[0]);
         close(sockdSock[0]);
+        close(sockdPipe[0]);
         // Don't share the RNG state with the master process.
         nk_random_u32_init(&cs.rnd32_state);
         sockd_main();

src/ndhc.h

@@ -67,10 +67,8 @@ struct client_config_t {
 
 extern struct client_config_t client_config;
 
-extern int pToIfchR;
-extern int pToIfchW;
-extern int pToNdhcR;
-extern int pToNdhcW;
+extern int ifchSock[2];
+extern int ifchPipe[2];
 extern int sockdSock[2];
 extern int sockdPipe[2];
 extern char state_dir[PATH_MAX];