3 files changed, 51 insertions, 30 deletions

diff --git a/erts/emulator/sys/unix/erl_child_setup.c b/erts/emulator/sys/unix/erl_child_setup.c
index f74cb0f356..fdffc7f119 100644
--- a/erts/emulator/sys/unix/erl_child_setup.c
+++ b/erts/emulator/sys/unix/erl_child_setup.c
@@ -426,6 +426,10 @@ main(int argc, char *argv[])
             while (write(pipes[1], &proto, sizeof(proto)) < 0 && errno == EINTR)
                 ; /* remove gcc warning */
 
+            proto.action = ErtsSysForkerProtoAction_StartAck;
+            while (write(uds_fd, &proto, sizeof(proto)) < 0 && errno == EINTR)
+                ; /* remove gcc warning */
+
             sys_sigrelease(SIGCHLD);
             close(pipes[0]);
             close(pipes[1]);
diff --git a/erts/emulator/sys/unix/erl_child_setup.h b/erts/emulator/sys/unix/erl_child_setup.h
index c3258f7cbe..93b39d46b2 100644
--- a/erts/emulator/sys/unix/erl_child_setup.h
+++ b/erts/emulator/sys/unix/erl_child_setup.h
@@ -45,6 +45,7 @@ typedef unsigned long long ErtsSysPortId;
 typedef struct ErtsSysForkerProto_ {
     enum {
         ErtsSysForkerProtoAction_Start,
+        ErtsSysForkerProtoAction_StartAck,
         ErtsSysForkerProtoAction_Go,
         ErtsSysForkerProtoAction_SigChld,
         ErtsSysForkerProtoAction_Ack
diff --git a/erts/emulator/sys/unix/sys_drivers.c b/erts/emulator/sys/unix/sys_drivers.c
index 82096e5779..dc1c00ff96 100644
--- a/erts/emulator/sys/unix/sys_drivers.c
+++ b/erts/emulator/sys/unix/sys_drivers.c
@@ -1761,37 +1761,59 @@ static void forker_ready_input(ErlDrvData e, ErlDrvEvent fd)
         erl_exit(ERTS_DUMP_EXIT, "erl_child_setup closed\n");
 
     ASSERT(res == sizeof(*proto));
-    ASSERT(proto->action == ErtsSysForkerProtoAction_SigChld);
-
-    /* ideally this would be a port_command call, but as command is
-       already used by the spawn_driver, we use control instead.
-       Note that when using erl_drv_port_control it is an asynchronous
-       control. */
-    erl_drv_port_control(proto->u.sigchld.port_id, 'S',
-                         (char*)proto, sizeof(*proto));
-
-}
 
-static void forker_ready_output(ErlDrvData e, ErlDrvEvent fd)
-{
-    ErlDrvPort port_num = (ErlDrvPort)e;
-
-    while(driver_sizeq(port_num) > 0) {
+    if (proto->action == ErtsSysForkerProtoAction_StartAck) {
+        /* Ideally we would like to not have to ack each Start
+           command being sent over the uds, but it would seem
+           that some operating systems (only observed on FreeBSD)
+           throw away data on the uds when the socket becomes full,
+           so we have to.
+
+           Also the freebsd manual explicitly states that
+           you should not close fds before they are known
+           to have reached the other side, so this Ack protects
+           against that as well.
+        */
+        ErlDrvPort port_num = (ErlDrvPort)e;
         int vlen;
         SysIOVec *iov = driver_peekq(port_num, &vlen);
         ErtsSysForkerProto *proto = (ErtsSysForkerProto *)iov[0].iov_base;
-        ASSERT(iov[0].iov_len >= (sizeof(*proto)));
-        if (sys_uds_write(forker_fd, (char*)proto, sizeof(*proto),
-                          proto->u.start.fds, 3, 0) < 0) {
-            if (errno == ERRNO_BLOCK)
-                return;
-            erl_exit(ERTS_DUMP_EXIT, "Failed to write to erl_child_setup: %d\n", errno);
-        }
+
         close(proto->u.start.fds[0]);
         close(proto->u.start.fds[1]);
         if (proto->u.start.fds[1] != proto->u.start.fds[2])
             close(proto->u.start.fds[2]);
+
         driver_deq(port_num, sizeof(*proto));
+
+        if (driver_sizeq(port_num) > 0)
+            driver_select(port_num, forker_fd, ERL_DRV_WRITE|ERL_DRV_USE, 1);
+    } else {
+        ASSERT(proto->action == ErtsSysForkerProtoAction_SigChld);
+
+        /* ideally this would be a port_command call, but as command is
+           already used by the spawn_driver, we use control instead.
+           Note that when using erl_drv_port_control it is an asynchronous
+           control. */
+        erl_drv_port_control(proto->u.sigchld.port_id, 'S',
+                             (char*)proto, sizeof(*proto));
+    }
+
+}
+
+static void forker_ready_output(ErlDrvData e, ErlDrvEvent fd)
+{
+    ErlDrvPort port_num = (ErlDrvPort)e;
+
+    int vlen;
+    SysIOVec *iov = driver_peekq(port_num, &vlen);
+    ErtsSysForkerProto *proto = (ErtsSysForkerProto *)iov[0].iov_base;
+    ASSERT(iov[0].iov_len >= (sizeof(*proto)));
+    if (sys_uds_write(forker_fd, (char*)proto, sizeof(*proto),
+                      proto->u.start.fds, 3, 0) < 0) {
+        if (errno == ERRNO_BLOCK)
+            return;
+        erl_exit(ERTS_DUMP_EXIT, "Failed to write to erl_child_setup uds: %d", errno);
     }
 
     driver_select(port_num, forker_fd, ERL_DRV_WRITE, 0);
@@ -1804,25 +1826,19 @@ static ErlDrvSSizeT forker_control(ErlDrvData e, unsigned int cmd, char *buf,
     ErlDrvPort port_num = (ErlDrvPort)e;
     int res;
 
-    if (driver_sizeq(port_num) > 0) {
-        driver_enq(port_num, buf, len);
+    driver_enq(port_num, buf, len);
+    if (driver_sizeq(port_num) > sizeof(*proto)) {
         return 0;
     }
 
     if ((res = sys_uds_write(forker_fd, (char*)proto, sizeof(*proto),
                              proto->u.start.fds, 3, 0)) < 0) {
         if (errno == ERRNO_BLOCK) {
-            driver_enq(port_num, buf, len);
             driver_select(port_num, forker_fd, ERL_DRV_WRITE|ERL_DRV_USE, 1);
             return 0;
         }
         erl_exit(ERTS_DUMP_EXIT, "Failed to write to erl_child_setup: %d\n", errno);
     }
 
-    ASSERT(res == sizeof(*proto));
-    close(proto->u.start.fds[0]);
-    close(proto->u.start.fds[1]);
-    if (proto->u.start.fds[1] != proto->u.start.fds[2])
-        close(proto->u.start.fds[2]);
     return 0;
 }