[v5,32/50] multi-process: Use separate MMIO communication channel

diff --git a/hw/proxy/qemu-proxy.c b/hw/proxy/qemu-proxy.c
index bcb24f7..68517aa 100644
--- a/hw/proxy/qemu-proxy.c
+++ b/hw/proxy/qemu-proxy.c
@@ -283,13 +283,14 @@  static int remote_spawn(PCIProxyDev *pdev, const char *opts,
                         const char *exec_name, Error **errp)
 {
     pid_t rpid;
-    int fd[2] = {-1, -1};
+    int fd[2], mmio[2];
     Error *local_error = NULL;
     char *argv[64];
     int argc = 0;
     char *sfd;
     char *exec_dir;
     int rc = -EINVAL;
+    struct timeval timeout = {.tv_sec = 10, .tv_usec = 0};
 
     if (pdev->managed) {
         /* Child is forked by external program (such as libvirt). */
@@ -302,7 +303,8 @@  static int remote_spawn(PCIProxyDev *pdev, const char *opts,
         return rc;
     }
 
-    if (socketpair(AF_UNIX, SOCK_STREAM, 0, fd)) {
+    if (socketpair(AF_UNIX, SOCK_STREAM, 0, fd) ||
+        socketpair(AF_UNIX, SOCK_STREAM, 0, mmio)) {
         error_setg(errp, "Unable to create unix socket.");
         return rc;
     }
@@ -310,6 +312,8 @@  static int remote_spawn(PCIProxyDev *pdev, const char *opts,
     argc = add_argv(exec_dir, argv, argc);
     sfd = g_strdup_printf("%d", fd[1]);
     argc = add_argv(sfd, argv, argc);
+    sfd = g_strdup_printf("%d", mmio[1]);
+    argc = add_argv(sfd, argv, argc);
     argc = make_argv((char *)opts, argv, argc);
 
     /* TODO: Restrict the forked process' permissions and capabilities. */
@@ -318,24 +322,35 @@  static int remote_spawn(PCIProxyDev *pdev, const char *opts,
     if (rpid == -1) {
         error_setg(errp, "Unable to spawn emulation program.");
         close(fd[0]);
-        goto fail;
+        close(fd[1]);
+        close(mmio[0]);
+        close(mmio[1]);
+        return rc;
     }
 
     if (rpid == 0) {
         close(fd[0]);
+        close(mmio[0]);
 
         rc = execv(argv[0], (char *const *)argv);
         exit(1);
     }
     pdev->remote_pid = rpid;
     pdev->socket = fd[0];
+    pdev->mmio_sock = mmio[0];
 
-    rc = 0;
+    rc = setsockopt(mmio[0], SOL_SOCKET, SO_RCVTIMEO, (char *)&timeout,
+                   sizeof(timeout));
+    if (rc < 0) {
+        close(fd[0]);
+        close(mmio[0]);
 
-fail:
-    close(fd[1]);
+        error_setg(errp, "Unable to set timeout for socket");
 
-    return rc;
+        return rc;
+    }
+
+    return 0;
 }
 
 static int get_proxy_sock(PCIDevice *dev)
@@ -523,6 +538,9 @@  static void init_proxy(PCIDevice *dev, char *command, char *exec_name,
     mpqemu_init_channel(pdev->mpqemu_link, &pdev->mpqemu_link->com,
                         pdev->socket);
 
+    mpqemu_init_channel(pdev->mpqemu_link, &pdev->mpqemu_link->mmio,
+                        pdev->mmio_sock);
+
     configure_memory_sync(pdev->sync, pdev->mpqemu_link);
 }
 
@@ -575,10 +593,10 @@  static void send_bar_access_msg(PCIProxyDev *dev, MemoryRegion *mr,
                                 unsigned size, bool memory)
 {
     MPQemuLinkState *mpqemu_link = dev->mpqemu_link;
-    MPQemuMsg msg;
-    int wait;
+    MPQemuMsg msg, ret;
 
     memset(&msg, 0, sizeof(MPQemuMsg));
+    memset(&ret, 0, sizeof(MPQemuMsg));
 
     msg.bytestream = 0;
     msg.size = sizeof(msg.data1);
@@ -590,19 +608,18 @@  static void send_bar_access_msg(PCIProxyDev *dev, MemoryRegion *mr,
         msg.cmd = BAR_WRITE;
         msg.data1.bar_access.val = *val;
     } else {
-        wait = GET_REMOTE_WAIT;
-
         msg.cmd = BAR_READ;
-        msg.num_fds = 1;
-        msg.fds[0] = wait;
     }
 
-    mpqemu_msg_send(&msg, mpqemu_link->com);
+    mpqemu_msg_send(&msg, mpqemu_link->mmio);
 
-    if (!write) {
-        *val = wait_for_remote(wait);
-        PUT_REMOTE_WAIT(wait);
+    if (write) {
+        return;
     }
+
+    mpqemu_msg_recv(&ret, mpqemu_link->mmio);
+
+    *val = ret.data1.mmio_ret.val;
 }
 
 void proxy_default_bar_write(void *opaque, hwaddr addr, uint64_t val,
diff --git a/include/hw/proxy/qemu-proxy.h b/include/hw/proxy/qemu-proxy.h
index f7666fb..2a2c732 100644
--- a/include/hw/proxy/qemu-proxy.h
+++ b/include/hw/proxy/qemu-proxy.h
@@ -58,6 +58,7 @@  struct PCIProxyDev {
     EventNotifier en_ping;
 
     int socket;
+    int mmio_sock;
 
     char *rid;
     char *dev_id;
diff --git a/include/io/mpqemu-link.h b/include/io/mpqemu-link.h
index aaaf1a4..3962630 100644
--- a/include/io/mpqemu-link.h
+++ b/include/io/mpqemu-link.h
@@ -61,6 +61,7 @@  typedef enum {
     GET_PCI_INFO,
     RET_PCI_INFO,
     PROXY_PING,
+    MMIO_RETURN,
     MAX,
 } mpqemu_cmd_t;
 
@@ -107,6 +108,10 @@  typedef struct {
 } ret_pci_info_msg_t;
 
 typedef struct {
+    uint64_t val;
+} mmio_ret_msg_t;
+
+typedef struct {
     mpqemu_cmd_t cmd;
     int bytestream;
     size_t size;
@@ -117,6 +122,7 @@  typedef struct {
         bar_access_msg_t bar_access;
         set_irqfd_msg_t set_irqfd;
         ret_pci_info_msg_t ret_pci_info;
+        mmio_ret_msg_t mmio_ret;
     } data1;
 
     int fds[REMOTE_MAX_FDS];
@@ -171,6 +177,7 @@  typedef struct MPQemuLinkState {
     GMainLoop *loop;
 
     MPQemuChannel *com;
+    MPQemuChannel *mmio;
 
     mpqemu_link_callback callback;
 } MPQemuLinkState;
diff --git a/io/mpqemu-link.c b/io/mpqemu-link.c
index 73b7032..07a9be9 100644
--- a/io/mpqemu-link.c
+++ b/io/mpqemu-link.c
@@ -57,6 +57,7 @@  void mpqemu_link_finalize(MPQemuLinkState *s)
     g_main_loop_quit(s->loop);
 
     mpqemu_destroy_channel(s->com);
+    mpqemu_destroy_channel(s->mmio);
 
     object_unref(OBJECT(s));
 }
@@ -330,6 +331,7 @@  void mpqemu_start_coms(MPQemuLinkState *s)
 {
 
     g_assert(g_source_attach(&s->com->gsrc, s->ctx));
+    g_assert(g_source_attach(&s->mmio->gsrc, s->ctx));
 
     g_main_loop_run(s->loop);
 }
diff --git a/qdev-monitor.c b/qdev-monitor.c
index ccd2ce0..27b2ddc 100644
--- a/qdev-monitor.c
+++ b/qdev-monitor.c
@@ -730,6 +730,7 @@  DeviceState *qdev_proxy_add(const char *rid, const char *id, char *bus,
     pdev->rid = g_strdup(rid);
     if (old_pdev) {
         pdev->socket = old_pdev->socket;
+        pdev->mmio_sock = old_pdev->mmio_sock;
         pdev->remote_pid = old_pdev->remote_pid;
     } else {
         pdev->socket = managed ? socket : -1;
diff --git a/remote/remote-main.c b/remote/remote-main.c
index 2c05d20..6cfc446 100644
--- a/remote/remote-main.c
+++ b/remote/remote-main.c
@@ -104,8 +104,8 @@  static void process_bar_write(MPQemuMsg *msg, Error **errp)
 static void process_bar_read(MPQemuMsg *msg, Error **errp)
 {
     bar_access_msg_t *bar_access = &msg->data1.bar_access;
+    MPQemuMsg ret = { 0 };
     AddressSpace *as;
-    int wait = msg->fds[0];
     MemTxResult res;
     uint64_t val = 0;
 
@@ -139,9 +139,10 @@  static void process_bar_read(MPQemuMsg *msg, Error **errp)
     }
 
 fail:
-    notify_proxy(wait, val);
-
-    PUT_REMOTE_WAIT(wait);
+    ret.cmd = MMIO_RETURN;
+    ret.data1.mmio_ret.val = val;
+    ret.size = sizeof(ret.data1);
+    mpqemu_msg_send(&ret, mpqemu_link->mmio);
 }
 
 static void process_get_pci_info_msg(PCIDevice *pci_dev, MPQemuMsg *msg)
@@ -456,7 +457,14 @@  int main(int argc, char *argv[])
 
     mpqemu_init_channel(mpqemu_link, &mpqemu_link->com, fd);
 
-    parse_cmdline(argc - 2, argv + 2, NULL);
+    fd = qemu_parse_fd(argv[2]);
+    if (fd == -1) {
+        printf("Failed to parse fd for remote process.\n");
+        return -EINVAL;
+    }
+    mpqemu_init_channel(mpqemu_link, &mpqemu_link->mmio, fd);
+
+    parse_cmdline(argc - 3, argv + 3, NULL);
 
     mpqemu_link_set_callback(mpqemu_link, process_msg);