0004-erlexec-nodename-from-ifaddr.patch

Derive node name from interface address

Some erlang programs are controlled via the erlang RPC interface, reachable
via a node name set on startup with the "-node" argument to erlexec. For
example, the node name "foo@127.0.0.1" indicates that the node named 'foo' is
reachable locally, via the loopback interface. However, erlang programs
running on a Nanos unikernel cannot be controlled by a process on the same
host and must instead be controlled over a network. When DHCP is used to
assign network interfaces, the fully qualified node name cannot be known when
staging the image with the preferred arguments. This patch allows the node
name for an instance to be set using the address of a specified interface. The
hostname in the -name argument may be set to "%<if>" where <if> is the
interface name.

For example, using the argument "-name foo@%en1" will cause erlexec to get the
configured address of interface "en1", waiting for it to be assigned via DHCP
if necessary, then use that address to compose the name as "foo@<ifaddr>",
where <ifaddr> is the address assigned to the interface.

diff --git a/erts/etc/common/erlexec.c b/erts/etc/common/erlexec.c
index 4c279ac..329b4fa 100644
--- a/erts/etc/common/erlexec.c
+++ b/erts/etc/common/erlexec.c
@@ -26,7 +26,11 @@
 #include "etc_common.h"
 
 #if defined(RUN_FROM_EMU)
-#  include "global.h"
+#include <sys/ioctl.h>
+#include <net/if.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+#include "global.h"
 #endif
 
 #include "erl_driver.h"
@@ -415,6 +419,70 @@ static void add_boot_config(void)
 # define ADD_BOOT_CONFIG
 #endif
 
+#ifdef RUN_FROM_EMU
+static char *process_nodename(char *namearg)
+{
+    int fd, waiting = 0;
+    char *hostname;
+    struct ifreq ifr;
+
+    hostname = strchr(namearg, '@');
+    if (!hostname)
+        return namearg;
+    hostname++;
+    if (hostname[0] != '%')
+        return namearg;
+
+    fd = socket(AF_INET, SOCK_DGRAM, 0);
+    if (fd < 0) {
+        fprintf(stderr, "%s: unable to open socket: %s\n", __func__, strerror(errno));
+        return namearg;
+    }
+
+    do {
+        struct sockaddr_in *sin;
+        ifr.ifr_addr.sa_family = AF_INET;
+        strncpy(ifr.ifr_name, hostname + 1, IFNAMSIZ-1);
+        if (ioctl(fd, SIOCGIFADDR, &ifr) < 0) {
+            fprintf(stderr, "%s: ioctl for SIOCGIFADDR failed: %s\n", __func__, strerror(errno));
+            close(fd);
+            return namearg;
+        }
+        sin = (struct sockaddr_in *)&ifr.ifr_addr;
+        if (sin->sin_addr.s_addr != 0) {
+            int sname_len = hostname - namearg;
+            int addr_len, total;
+            char *addr;
+            char *newnode;
+
+            if (waiting)
+                fprintf(stderr, "\n");
+            close(fd);
+            addr = inet_ntoa(sin->sin_addr);
+            addr_len = strlen(addr);
+            total = sname_len + addr_len + 1;
+            newnode = malloc(total);
+            if (!newnode) {
+                fprintf(stderr, "%s: unable to allocate %d bytes for node name\n", __func__, total);
+                return namearg;
+            }
+            strncpy(newnode, namearg, sname_len);
+            strncpy(newnode + sname_len, addr, addr_len + 1);
+            newnode[total - 1] = '\0';
+            fprintf(stderr, "%s: node name is \"%s\"\n", progname, newnode);
+            return newnode;
+        }
+        if (!waiting) {
+            waiting = 1;
+            fprintf(stderr, "%s: waiting for address assignment for interface \"%s\"...\n",
+                    progname, hostname + 1);
+        } else {
+            fprintf(stderr, ".");
+        }
+        sleep(1);
+    } while (1);
+}
+#endif
 
 #ifdef __WIN32__
 __declspec(dllexport) int win_erlexec(int argc, char **argv, HANDLE module, int windowed)
@@ -745,7 +813,11 @@ int main(int argc, char **argv)
 			 */
 
 			add_arg(argv[i]);
+#ifdef RUN_FROM_EMU
+			add_arg(process_nodename(argv[i+1]));
+#else
 			add_arg(argv[i+1]);
+#endif
 			isdistributed = 1;
 			i++;
 		    } else if (strcmp(argv[i], "-noinput") == 0) {