erts: Move os_pid to port hash to child setup

Had to move the hashing because of a race that can otherwise happen
where a new os_pid value was inserted into the hash before the
previous value had been removed.

Also replaced the protocol inbetween erts and child setup to be
a binary protocol. This was done in order to deal with the varying
size of Eterm.

4 files changed, 250 insertions, 165 deletions

diff --git a/erts/emulator/sys/unix/erl_child_setup.c b/erts/emulator/sys/unix/erl_child_setup.c
index 1f7ead0ec3..f74cb0f356 100644
--- a/erts/emulator/sys/unix/erl_child_setup.c
+++ b/erts/emulator/sys/unix/erl_child_setup.c
@@ -60,6 +60,8 @@
 
 #include "erl_driver.h"
 #include "sys_uds.h"
+#include "hash.h"
+#include "erl_child_setup.h"
 
 #define SET_CLOEXEC(fd) fcntl(fd, F_SETFD, fcntl(fd, F_GETFD) | FD_CLOEXEC)
 
@@ -105,6 +107,10 @@ void sys_sigrelease(int sig)
     sigprocmask(SIG_UNBLOCK, &mask, (sigset_t *)NULL);
 }
 
+static void add_os_pid_to_port_id_mapping(Eterm, pid_t);
+static Eterm get_port_id(pid_t);
+static int forker_hash_init(void);
+
 static int max_files = -1;
 static int sigchld_pipe[2];
 
@@ -114,7 +120,7 @@ start_new_child(int pipes[])
     int size, res, i, pos = 0;
     char *buff, *o_buff;
 
-    char *cmd, *wd, **new_environ, **args = NULL, cbuff[1];
+    char *cmd, *wd, **new_environ, **args = NULL;
 
     Sint cnt, flags;
 
@@ -194,7 +200,12 @@ start_new_child(int pipes[])
 
     DEBUG_PRINT("read ack");
     do {
-        res = read(pipes[0], cbuff, 1);
+        ErtsSysForkerProto proto;
+        res = read(pipes[0], &proto, sizeof(proto));
+        if (res > 0) {
+            ASSERT(proto.action == ErtsSysForkerProtoAction_Ack);
+            ASSERT(res == sizeof(proto));
+        }
     } while(res < 0 && (errno == EINTR || errno == ERRNO_BLOCK));
     if (res < 1) {
         errno = EPIPE;
@@ -355,6 +366,8 @@ main(int argc, char *argv[])
         exit(1);
     }
 
+    forker_hash_init();
+
     SET_CLOEXEC(uds_fd);
 
     DEBUG_PRINT("Starting forker %d", max_files);
@@ -376,9 +389,10 @@ main(int argc, char *argv[])
 
         if (FD_ISSET(uds_fd, &read_fds)) {
             int pipes[3], res, os_pid;
-            char buff[256];
+            ErtsSysForkerProto proto;
             errno = 0;
-            if ((res = sys_uds_read(uds_fd, buff, 1, pipes, 3, MSG_DONTWAIT)) < 0) {
+            if ((res = sys_uds_read(uds_fd, (char*)&proto, sizeof(proto),
+                                    pipes, 3, MSG_DONTWAIT)) < 0) {
                 if (errno == EINTR)
                     continue;
                 DEBUG_PRINT("erl_child_setup failed to read from uds: %d, %d", res, errno);
@@ -391,8 +405,8 @@ main(int argc, char *argv[])
             }
             /* Since we use unix domain sockets and send the entire data in
                one go we *should* get the entire payload at once. */
-            ASSERT(res == 1);
-            ASSERT(buff[0] == 'S');
+            ASSERT(res == sizeof(proto));
+            ASSERT(proto.action == ErtsSysForkerProtoAction_Start);
 
             sys_sigblock(SIGCHLD);
 
@@ -402,10 +416,14 @@ main(int argc, char *argv[])
             if (os_pid == 0)
                 start_new_child(pipes);
 
+            add_os_pid_to_port_id_mapping(proto.u.start.port_id, os_pid);
+
             /* We write an ack here, but expect the reply on
                the pipes[0] inside the fork */
-            res = sprintf(buff,"GO:%010d:%010d", os_pid, errno);
-            while (write(pipes[1], buff, res + 1) < 0 && errno == EINTR)
+            proto.action = ErtsSysForkerProtoAction_Go;
+            proto.u.go.os_pid = os_pid;
+            proto.u.go.error_number = errno;
+            while (write(pipes[1], &proto, sizeof(proto)) < 0 && errno == EINTR)
                 ; /* remove gcc warning */
 
             sys_sigrelease(SIGCHLD);
@@ -416,16 +434,23 @@ main(int argc, char *argv[])
 
         if (FD_ISSET(sigchld_pipe[0], &read_fds)) {
             int ibuff[2];
-            char buff[256];
+            ErtsSysForkerProto proto;
             res = read(sigchld_pipe[0], ibuff, sizeof(ibuff));
             if (res <= 0) {
                 if (errno == EINTR)
                     continue;
                 ABORT("Failed to read from sigchld pipe: %d (%d)", res, errno);
             }
-            res = snprintf(buff, 256, "SIGCHLD:%010d:%010d", ibuff[0], ibuff[1]);
+
+            proto.u.sigchld.port_id = get_port_id((pid_t)(ibuff[0]));
+
+            if (proto.u.sigchld.port_id == THE_NON_VALUE)
+                continue; /* exit status report not requested */
+
+            proto.action = ErtsSysForkerProtoAction_SigChld;
+            proto.u.sigchld.error_number = ibuff[1];
             DEBUG_PRINT("send %s to %d", buff, uds_fd);
-            if (write(uds_fd, buff, res + 1) < 0) {
+            if (write(uds_fd, &proto, sizeof(proto)) < 0) {
                 if (errno == EINTR)
                     continue;
                 /* The uds was close, which most likely means that the VM
@@ -437,3 +462,83 @@ main(int argc, char *argv[])
     }
     return 1;
 }
+
+typedef struct exit_status {
+    HashBucket hb;
+    pid_t os_pid;
+    Eterm port_id;
+} ErtsSysExitStatus;
+
+static Hash *forker_hash;
+
+static void add_os_pid_to_port_id_mapping(Eterm port_id, pid_t os_pid)
+{
+    if (port_id != THE_NON_VALUE) {
+        /* exit status report requested */
+        ErtsSysExitStatus es;
+        es.os_pid = os_pid;
+        es.port_id = port_id;
+        hash_put(forker_hash, &es);
+    }
+}
+
+static Eterm get_port_id(pid_t os_pid)
+{
+    ErtsSysExitStatus est, *es;
+    Eterm port_id;
+    est.os_pid = os_pid;
+    es = hash_remove(forker_hash, &est);
+    if (!es) return THE_NON_VALUE;
+    port_id = es->port_id;
+    free(es);
+    return port_id;
+}
+
+static int fcmp(void *a, void *b)
+{
+    ErtsSysExitStatus *sa = a;
+    ErtsSysExitStatus *sb = b;
+    return !(sa->os_pid == sb->os_pid);
+}
+
+static HashValue fhash(void *e)
+{
+    ErtsSysExitStatus *se = e;
+    Uint32 val = se->os_pid;
+    val = (val+0x7ed55d16) + (val<<12);
+    val = (val^0xc761c23c) ^ (val>>19);
+    val = (val+0x165667b1) + (val<<5);
+    val = (val+0xd3a2646c) ^ (val<<9);
+    val = (val+0xfd7046c5) + (val<<3);
+    val = (val^0xb55a4f09) ^ (val>>16);
+    return val;
+}
+
+static void *falloc(void *e)
+{
+    ErtsSysExitStatus *se = e;
+    ErtsSysExitStatus *ne = malloc(sizeof(ErtsSysExitStatus));
+    ne->os_pid = se->os_pid;
+    ne->port_id = se->port_id;
+    return ne;
+}
+
+static void *meta_alloc(int type, size_t size) { return malloc(size); }
+static void meta_free(int type, void *p)       { free(p); }
+
+static int forker_hash_init(void)
+{
+    HashFunctions forker_hash_functions;
+    forker_hash_functions.hash = fhash;
+    forker_hash_functions.cmp = fcmp;
+    forker_hash_functions.alloc = falloc;
+    forker_hash_functions.free = free;
+    forker_hash_functions.meta_alloc = meta_alloc;
+    forker_hash_functions.meta_free  = meta_free;
+    forker_hash_functions.meta_print = NULL;
+
+    forker_hash = hash_new(0, "forker_hash",
+                           16, forker_hash_functions);
+
+    return 1;
+}
diff --git a/erts/emulator/sys/unix/erl_child_setup.h b/erts/emulator/sys/unix/erl_child_setup.h
new file mode 100644
index 0000000000..c3258f7cbe
--- /dev/null
+++ b/erts/emulator/sys/unix/erl_child_setup.h
@@ -0,0 +1,68 @@
+/*
+ * %CopyrightBegin%
+ * 
+ * Copyright Ericsson AB 2015-2015. All Rights Reserved.
+ * 
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ * 
+ * %CopyrightEnd%
+ *
+ * This file defines the interface inbetween erts and child_setup.
+ */
+
+#ifndef _ERL_UNIX_FORKER_H
+#define _ERL_UNIX_FORKER_H
+
+#include "sys.h"
+
+#define FORKER_ARGV_NO_OF_ARGS  3
+#define FORKER_ARGV_PROGNAME_IX	0    /* Program name                          */
+#define FORKER_ARGV_MAX_FILES	1    /* max_files                             */
+
+#define FORKER_FLAG_USE_STDIO   (1 << 0)    /* dup the pipe to stdin/stderr   */
+#define FORKER_FLAG_EXIT_STATUS (1 << 1)    /* send the exit status to parent */
+#define FORKER_FLAG_DO_READ     (1 << 2)    /* dup write fd */
+#define FORKER_FLAG_DO_WRITE    (1 << 3)    /* dup read  fd  */
+
+#if SIZEOF_VOID_P == SIZEOF_LONG
+typedef unsigned long ErtsSysPortId;
+#elif SIZEOF_VOID_P == SIZEOF_INT
+typedef unsigned int ErtsSysPortId;
+#elif SIZEOF_VOID_P == SIZEOF_LONG_LONG
+typedef unsigned long long ErtsSysPortId;
+#endif
+
+typedef struct ErtsSysForkerProto_ {
+    enum {
+        ErtsSysForkerProtoAction_Start,
+        ErtsSysForkerProtoAction_Go,
+        ErtsSysForkerProtoAction_SigChld,
+        ErtsSysForkerProtoAction_Ack
+    } action;
+    union {
+        struct {
+            ErtsSysPortId port_id;
+            int fds[3];
+        } start;
+        struct {
+            pid_t os_pid;
+            int error_number;
+        } go;
+        struct {
+            ErtsSysPortId port_id;
+            int error_number;
+        } sigchld;
+    } u;
+} ErtsSysForkerProto;
+
+#endif /* #ifndef _ERL_UNIX_FORKER_H */
diff --git a/erts/emulator/sys/unix/erl_unix_sys.h b/erts/emulator/sys/unix/erl_unix_sys.h
index c46f2c1fa2..0352ee1b3c 100644
--- a/erts/emulator/sys/unix/erl_unix_sys.h
+++ b/erts/emulator/sys/unix/erl_unix_sys.h
@@ -410,15 +410,6 @@ void erts_sys_unblock_fpe(int);
 #define ERTS_FP_ERROR_THOROUGH(p, f, A)	__ERTS_FP_ERROR_THOROUGH(&(p)->fp_exception, f, A)
 
 
-#define FORKER_ARGV_NO_OF_ARGS  3
-#define FORKER_ARGV_PROGNAME_IX	0    /* Program name                          */
-#define FORKER_ARGV_MAX_FILES	1    /* max_files                             */
-
-#define FORKER_FLAG_USE_STDIO   (1 << 0)    /* dup the pipe to stdin/stderr   */
-#define FORKER_FLAG_EXIT_STATUS (1 << 1)    /* send the exit status to parent */
-#define FORKER_FLAG_DO_READ     (1 << 2)    /* dup write fd */
-#define FORKER_FLAG_DO_WRITE    (1 << 3)    /* dup read fd  */
-
 /* Threads */
 #ifdef USE_THREADS
 extern int init_async(int);
diff --git a/erts/emulator/sys/unix/sys_drivers.c b/erts/emulator/sys/unix/sys_drivers.c
index 6a1f2f6b2c..82096e5779 100644
--- a/erts/emulator/sys/unix/sys_drivers.c
+++ b/erts/emulator/sys/unix/sys_drivers.c
@@ -76,6 +76,8 @@ static Eterm forker_port;
 #include "erl_sys_driver.h"
 #include "sys_uds.h"
 
+#include "erl_child_setup.h"
+
 #if defined IOV_MAX
 #define MAXIOV IOV_MAX
 #elif defined UIO_MAXIOV
@@ -120,12 +122,6 @@ typedef struct driver_data {
     ErtsSysBlocking *blocking;
 } ErtsSysDriverData;
 
-typedef struct exit_status {
-    HashBucket hb;
-    pid_t os_pid;
-    Eterm port_id;
-} ErtsSysExitStatus;
-
 #define DIR_SEPARATOR_CHAR    '/'
 
 #if defined(__ANDROID__)
@@ -241,21 +237,18 @@ static void outputv(ErlDrvData, ErlIOVec*);
 static void stop_select(ErlDrvEvent, void*);
 
 /* II.V Forker prototypes */
-static int forker_init(void);
 static ErlDrvData forker_start(ErlDrvPort, char*, SysDriverOpts*);
 static void forker_stop(ErlDrvData);
 static void forker_ready_input(ErlDrvData, ErlDrvEvent);
 static void forker_ready_output(ErlDrvData, ErlDrvEvent);
 static ErlDrvSSizeT forker_control(ErlDrvData, unsigned int, char *,
                                    ErlDrvSizeT, char **, ErlDrvSizeT);
-static void forker_add_os_pid_mapping(ErtsSysDriverData *);
-static void forker_remove_os_pid_mapping(ErtsSysDriverData *);
 
 /* III Driver entries */
 
 /* III.I The spawn driver */
 struct erl_drv_entry spawn_driver_entry = {
-    forker_init,
+    NULL,
     spawn_start,
     stop,
     output,
@@ -794,12 +787,16 @@ static ErlDrvData spawn_start(ErlDrvPort port_num, char* name,
 
     {
         /* send ofd[0] + ifd[1] + stderrfd to forker port */
-        int *fds = erts_alloc(ERTS_ALC_T_DRV_CTRL_DATA, sizeof(int)*3);
-        memset(fds, 0, sizeof(int)*3);
-        fds[0] = ofd[0];
-        fds[1] = ifd[1];
-        fds[2] = stderrfd;
-        if (erl_drv_port_control(forker_port, 'S', (char*)fds, sizeof(int)*3)) {
+        ErtsSysForkerProto *proto =
+            erts_alloc(ERTS_ALC_T_DRV_CTRL_DATA,
+                       sizeof(ErtsSysForkerProto));
+        memset(proto, 0, sizeof(ErtsSysForkerProto));
+        proto->action = ErtsSysForkerProtoAction_Start;
+        proto->u.start.fds[0] = ofd[0];
+        proto->u.start.fds[1] = ifd[1];
+        proto->u.start.fds[2] = stderrfd;
+        proto->u.start.port_id = opts->exit_status ? erts_drvport2id(port_num) : THE_NON_VALUE;
+        if (erl_drv_port_control(forker_port, 'S', (char*)proto, sizeof(*proto))) {
             /* The forker port has been killed, we close both fd's which will
                make open_port throw an epipe error */
             close(ofd[0]);
@@ -824,8 +821,12 @@ static ErlDrvSSizeT spawn_control(ErlDrvData e, unsigned int cmd, char *buf,
                                   ErlDrvSizeT len, char **rbuf, ErlDrvSizeT rlen)
 {
     ErtsSysDriverData *dd = (ErtsSysDriverData*)e;
+    ErtsSysForkerProto *proto = (ErtsSysForkerProto *)buf;
 
-    memcpy(&dd->status, buf, sizeof(dd->status));
+    ASSERT(len == sizeof(*proto));
+    ASSERT(proto->action == ErtsSysForkerProtoAction_SigChld);
+
+    dd->status = proto->u.sigchld.error_number;
     dd->alive = -1;
 
     if (dd->ifd)
@@ -1134,10 +1135,6 @@ static void stop(ErlDrvData ev)
     ErtsSysDriverData* dd = (ErtsSysDriverData*)ev;
     ErlDrvPort prt = dd->port_num;
 
-    if (dd->alive == 1)
-        /* Stop has been called before the exit status has been reported */
-        forker_remove_os_pid_mapping(dd);
-
     if (dd->ifd) {
         nbio_stop_fd(prt, dd->ifd);
         driver_select(prt, abs(dd->ifd->fd), ERL_DRV_USE, 0);  /* close(ifd); */
@@ -1354,10 +1351,10 @@ static void ready_input(ErlDrvData e, ErlDrvEvent ready_fd)
 
     if (dd->pid == 0) {
         /* the pid is sent from erl_child_setup. spawn driver only. */
-        char message_buffer[3 + 10 + 1 + 10 + 1];
-        int reason, res;
+        ErtsSysForkerProto proto;
+        int res;
 
-        if((res = read(ready_fd, message_buffer, sizeof(message_buffer))) <= 0) {
+        if((res = read(ready_fd, &proto, sizeof(proto))) <= 0) {
             /* hmm, child setup seems to have closed the pipe too early...
                we close the port as there is not much else we can do */
             if (res < 0 && errno == ERRNO_BLOCK)
@@ -1369,21 +1366,25 @@ static void ready_input(ErlDrvData e, ErlDrvEvent ready_fd)
             return;
         }
 
-        if(sscanf(message_buffer,"GO:%010d:%010d", &dd->pid, &reason) == 2) {
-            if (dd->pid == -1) {
-                /* Setup failed! The only reason why this should happen is if
-                   the fork fails. */
-                errno = reason;
-                port_inp_failure(dd, -1);
-                return;
-            }
+        ASSERT(proto.action == ErtsSysForkerProtoAction_Go);
+        dd->pid = proto.u.go.os_pid;
+
+        if (dd->pid == -1) {
+            /* Setup failed! The only reason why this should happen is if
+               the fork fails. */
+            errno = proto.u.go.error_number;
+            port_inp_failure(dd, -1);
+            return;
+        }
+
+        proto.action = ErtsSysForkerProtoAction_Ack;
 
-            if (driver_sizeq(port_num) > 0) {
-                driver_enq(port_num, "A", 1);
+        if (driver_sizeq(port_num) > 0) {
+            driver_enq(port_num, (char*)&proto, sizeof(proto));
             } else {
-                if (write(abs(dd->ofd->fd), "A", 1) < 0)
+                if (write(abs(dd->ofd->fd), &proto, sizeof(proto)) < 0)
                     if (errno == ERRNO_BLOCK || errno == EINTR)
-                        driver_enq(port_num, "A", 1);
+                        driver_enq(port_num, (char*)&proto, sizeof(proto));
                 /* do nothing on failure here. If the ofd is broken, then
                    the ifd will probably also be broken and trigger
                    a port_inp_failure */
@@ -1400,15 +1401,9 @@ static void ready_input(ErlDrvData e, ErlDrvEvent ready_fd)
                    child setup will close this fd if fd < 0 */
                 driver_select(port_num, abs(dd->ofd->fd), ERL_DRV_WRITE|ERL_DRV_USE, 1);
 
-            if (dd->alive == 1)
-                forker_add_os_pid_mapping(dd);
-
             erl_drv_set_os_pid(port_num, dd->pid);
             erl_drv_init_ack(port_num, e);
             return;
-        }
-        ASSERT(0);
-        return;
     }
 
     if (packet_bytes == 0) {
@@ -1652,10 +1647,6 @@ void fd_ready_async(ErlDrvData drv_data,
 /* Forker driver */
 
 static int forker_fd;
-static Hash *forker_hash;
-static erts_smp_mtx_t forker_hash_mtx;
-
-static void ffree(void *e);
 
 static ErlDrvData forker_start(ErlDrvPort port_num, char* name,
                                SysDriverOpts* opts)
@@ -1749,16 +1740,18 @@ static ErlDrvData forker_start(ErlDrvPort port_num, char* name,
 
 static void forker_stop(ErlDrvData e)
 {
-    /* we probably should do something here */
+    /* we probably should do something here,
+       the port has been closed by the user. */
 }
 
 static void forker_ready_input(ErlDrvData e, ErlDrvEvent fd)
 {
-    int res, *exit_status;
-    char buff[8+10+1+10+1] = {0};
-    ErtsSysExitStatus est, *es;
+    int res;
+    ErtsSysForkerProto *proto;
+
+    proto = erts_alloc(ERTS_ALC_T_DRV_CTRL_DATA, sizeof(*proto));
 
-    if ((res = read(fd, buff, sizeof(buff))) < 0) {
+    if ((res = read(fd, proto, sizeof(*proto))) < 0) {
         if (errno == ERRNO_BLOCK)
             return;
         erl_exit(ERTS_DUMP_EXIT, "Failed to read from erl_child_setup: %d\n", errno);
@@ -1767,26 +1760,15 @@ static void forker_ready_input(ErlDrvData e, ErlDrvEvent fd)
     if (res == 0)
         erl_exit(ERTS_DUMP_EXIT, "erl_child_setup closed\n");
 
-    if (sscanf(buff, "SIGCHLD:%010d:%010d", &est.os_pid, &res) != 2)
-        erl_exit(ERTS_DUMP_EXIT, "Got corrupt data from erl_child_setup: %.s\n",
-                 buff, sizeof(buff));
-
-    erts_smp_mtx_lock(&forker_hash_mtx);
-    es = hash_remove(forker_hash, &est);
-    erts_smp_mtx_unlock(&forker_hash_mtx);
+    ASSERT(res == sizeof(*proto));
+    ASSERT(proto->action == ErtsSysForkerProtoAction_SigChld);
 
-    if (!es)
-        return;
-
-    exit_status = erts_alloc(ERTS_ALC_T_DRV_CTRL_DATA, sizeof(int));
-    exit_status[0] = res;
     /* 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(es->port_id, 'S', (char*)exit_status, sizeof(int));
-
-    ffree(es);
+    erl_drv_port_control(proto->u.sigchld.port_id, 'S',
+                         (char*)proto, sizeof(*proto));
 
 }
 
@@ -1797,18 +1779,19 @@ static void forker_ready_output(ErlDrvData e, ErlDrvEvent fd)
     while(driver_sizeq(port_num) > 0) {
         int vlen;
         SysIOVec *iov = driver_peekq(port_num, &vlen);
-        int *fds = (int*)iov[0].iov_base;
-        ASSERT(iov[0].iov_len >= sizeof(int)*3);
-        if (sys_uds_write(forker_fd, "S", 1, fds, 3, 0) < 0) {
+        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(fds[0]);
-        close(fds[1]);
-        if (fds[1] != fds[2])
-            close(fds[2]);
-        driver_deq(port_num, sizeof(int)*3);
+        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));
     }
 
     driver_select(port_num, forker_fd, ERL_DRV_WRITE, 0);
@@ -1817,7 +1800,7 @@ static void forker_ready_output(ErlDrvData e, ErlDrvEvent fd)
 static ErlDrvSSizeT forker_control(ErlDrvData e, unsigned int cmd, char *buf,
                                    ErlDrvSizeT len, char **rbuf, ErlDrvSizeT rlen)
 {
-    int *fds = (int*)buf;
+    ErtsSysForkerProto *proto = (ErtsSysForkerProto *)buf;
     ErlDrvPort port_num = (ErlDrvPort)e;
     int res;
 
@@ -1826,7 +1809,8 @@ static ErlDrvSSizeT forker_control(ErlDrvData e, unsigned int cmd, char *buf,
         return 0;
     }
 
-    if ((res = sys_uds_write(forker_fd, "S", 1, fds, 3, 0)) < 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);
@@ -1834,74 +1818,11 @@ static ErlDrvSSizeT forker_control(ErlDrvData e, unsigned int cmd, char *buf,
         }
         erl_exit(ERTS_DUMP_EXIT, "Failed to write to erl_child_setup: %d\n", errno);
     }
-    close(fds[0]);
-    close(fds[1]);
-    if (fds[1] != fds[2])
-        close(fds[2]);
-    return 0;
-}
 
-static void forker_add_os_pid_mapping(ErtsSysDriverData *dd)
-{
-    Eterm port_id = erts_drvport2id(dd->port_num);
-    ErtsSysExitStatus es;
-    es.os_pid = dd->pid;
-    es.port_id = port_id;
-    erts_smp_mtx_lock(&forker_hash_mtx);
-    hash_put(forker_hash, &es);
-    erts_smp_mtx_unlock(&forker_hash_mtx);
-}
-
-static void forker_remove_os_pid_mapping(ErtsSysDriverData *dd)
-{
-    ErtsSysExitStatus est, *es;
-    est.os_pid = dd->pid;
-    erts_smp_mtx_lock(&forker_hash_mtx);
-    es = hash_remove(forker_hash, &est);
-    erts_smp_mtx_unlock(&forker_hash_mtx);
-    if (es)
-        ffree(es);
-}
-
-static int fcmp(void *a, void *b)
-{
-    ErtsSysExitStatus *sa = a;
-    ErtsSysExitStatus *sb = b;
-    return !(sa->os_pid == sb->os_pid);
-}
-
-static HashValue fhash(void *e)
-{
-    ErtsSysExitStatus *se = e;
-    return make_hash2(make_small(se->os_pid));
-}
-
-static void *falloc(void *e)
-{
-    ErtsSysExitStatus *se = e;
-    ErtsSysExitStatus *ne = erts_alloc(ERTS_ALC_T_DRV, sizeof(ErtsSysExitStatus));
-    erts_smp_atomic_add_nob(&sys_misc_mem_sz, sizeof(ErtsSysBlocking));
-    ne->os_pid = se->os_pid;
-    ne->port_id = se->port_id;
-    return ne;
-}
-
-static void ffree(void *e)
-{
-    erts_free(ERTS_ALC_T_DRV, e);
-    erts_smp_atomic_add_nob(&sys_misc_mem_sz, -sizeof(ErtsSysBlocking));
-}
-
-static int forker_init(void)
-{
-    HashFunctions forker_hash_functions;
-    forker_hash_functions.hash = fhash;
-    forker_hash_functions.cmp = fcmp;
-    forker_hash_functions.alloc = falloc;
-    forker_hash_functions.free = ffree;
-    forker_hash = hash_new(ERTS_ALC_T_DRV, "forker_hash",
-                           16, forker_hash_functions);
-    erts_smp_mtx_init(&forker_hash_mtx, "forker_hash_mtx");
-
-    return 1;
+    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;
 }