virtiofsd: Start wiring up vhost-user

Listen on our unix socket for the connection from QEMU, when we get it
initialise vhost-user and dive into our own loop variant (currently
dummy).

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

tools/virtiofsd/fuse_i.h

@@ -13,6 +13,8 @@
 #include "fuse.h"
 #include "fuse_lowlevel.h"
 
+struct fv_VuDev;
+
 struct fuse_req {
     struct fuse_session *se;
     uint64_t unique;
@@ -65,6 +67,8 @@ struct fuse_session {
     size_t bufsize;
     int error;
     char *vu_socket_path;
+    int   vu_socketfd;
+    struct fv_VuDev *virtio_dev;
 };
 
 struct fuse_chan {

tools/virtiofsd/fuse_lowlevel.c

@@ -2242,6 +2242,11 @@ void fuse_session_unmount(struct fuse_session *se)
 {
 }
 
+int fuse_lowlevel_is_virtio(struct fuse_session *se)
+{
+    return se->vu_socket_path != NULL;
+}
+
 #ifdef linux
 int fuse_req_getgroups(fuse_req_t req, int size, gid_t list[])
 {

tools/virtiofsd/fuse_lowlevel.h

@@ -1755,6 +1755,13 @@ void fuse_req_interrupt_func(fuse_req_t req, fuse_interrupt_func_t func,
  */
 int fuse_req_interrupted(fuse_req_t req);
 
+/**
+ * Check if the session is connected via virtio
+ *
+ * @param se session object
+ * @return 1 if the session is a virtio session
+ */
+int fuse_lowlevel_is_virtio(struct fuse_session *se);
 
 /*
  * Inquiry functions

tools/virtiofsd/fuse_virtio.c

@@ -19,18 +19,78 @@
 
 #include <stdint.h>
 #include <stdio.h>
+#include <stdlib.h>
 #include <string.h>
 #include <sys/socket.h>
 #include <sys/types.h>
 #include <sys/un.h>
 #include <unistd.h>
 
+#include "contrib/libvhost-user/libvhost-user.h"
+
+/*
+ * We pass the dev element into libvhost-user
+ * and then use it to get back to the outer
+ * container for other data.
+ */
+struct fv_VuDev {
+    VuDev dev;
+    struct fuse_session *se;
+};
+
 /* From spec */
 struct virtio_fs_config {
     char tag[36];
     uint32_t num_queues;
 };
 
+/*
+ * Callback from libvhost-user if there's a new fd we're supposed to listen
+ * to, typically a queue kick?
+ */
+static void fv_set_watch(VuDev *dev, int fd, int condition, vu_watch_cb cb,
+                         void *data)
+{
+    fuse_log(FUSE_LOG_WARNING, "%s: TODO! fd=%d\n", __func__, fd);
+}
+
+/*
+ * Callback from libvhost-user if we're no longer supposed to listen on an fd
+ */
+static void fv_remove_watch(VuDev *dev, int fd)
+{
+    fuse_log(FUSE_LOG_WARNING, "%s: TODO! fd=%d\n", __func__, fd);
+}
+
+/* Callback from libvhost-user to panic */
+static void fv_panic(VuDev *dev, const char *err)
+{
+    fuse_log(FUSE_LOG_ERR, "%s: libvhost-user: %s\n", __func__, err);
+    /* TODO: Allow reconnects?? */
+    exit(EXIT_FAILURE);
+}
+
+static bool fv_queue_order(VuDev *dev, int qidx)
+{
+    return false;
+}
+
+static const VuDevIface fv_iface = {
+    /* TODO: Add other callbacks */
+    .queue_is_processed_in_order = fv_queue_order,
+};
+
+int virtio_loop(struct fuse_session *se)
+{
+    fuse_log(FUSE_LOG_INFO, "%s: Entry\n", __func__);
+
+    while (1) {
+        /* TODO: Add stuffing */
+    }
+
+    fuse_log(FUSE_LOG_INFO, "%s: Exit\n", __func__);
+}
+
 int virtio_session_mount(struct fuse_session *se)
 {
     struct sockaddr_un un;
@@ -75,5 +135,30 @@ int virtio_session_mount(struct fuse_session *se)
         return -1;
     }
 
+    fuse_log(FUSE_LOG_INFO, "%s: Waiting for vhost-user socket connection...\n",
+             __func__);
+    int data_sock = accept(listen_sock, NULL, NULL);
+    if (data_sock == -1) {
+        fuse_log(FUSE_LOG_ERR, "vhost socket accept: %m\n");
+        close(listen_sock);
         return -1;
+    }
+    close(listen_sock);
+    fuse_log(FUSE_LOG_INFO, "%s: Received vhost-user socket connection\n",
+             __func__);
+
+    /* TODO: Some cleanup/deallocation! */
+    se->virtio_dev = calloc(sizeof(struct fv_VuDev), 1);
+    if (!se->virtio_dev) {
+        fuse_log(FUSE_LOG_ERR, "%s: virtio_dev calloc failed\n", __func__);
+        close(data_sock);
+        return -1;
+    }
+
+    se->vu_socketfd = data_sock;
+    se->virtio_dev->se = se;
+    vu_init(&se->virtio_dev->dev, 2, se->vu_socketfd, fv_panic, fv_set_watch,
+            fv_remove_watch, &fv_iface);
+
+    return 0;
 }

tools/virtiofsd/fuse_virtio.h

@@ -20,4 +20,6 @@ struct fuse_session;
 
 int virtio_session_mount(struct fuse_session *se);
 
+int virtio_loop(struct fuse_session *se);
+
 #endif

tools/virtiofsd/passthrough_ll.c

@@ -36,6 +36,7 @@
  */
 
 #include "qemu/osdep.h"
+#include "fuse_virtio.h"
 #include "fuse_lowlevel.h"
 #include <assert.h>
 #include <dirent.h>
@@ -1395,11 +1396,7 @@ int main(int argc, char *argv[])
     fuse_daemonize(opts.foreground);
 
     /* Block until ctrl+c or fusermount -u */
-    if (opts.singlethread) {
-        ret = fuse_session_loop(se);
-    } else {
-        ret = fuse_session_loop_mt(se, opts.clone_fd);
-    }
+    ret = virtio_loop(se);
 
     fuse_session_unmount(se);
 err_out3: