virtiofsd: Open vhost connection instead of mounting

When run with vhost-user options we conect to the QEMU instead
via a socket.  Start this off by creating the socket.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Misono Tomohiro <misono.tomohiro@jp.fujitsu.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

tools/virtiofsd/fuse_i.h

@@ -6,9 +6,10 @@
  * See the file COPYING.LIB
  */
 
+#ifndef FUSE_I_H
+#define FUSE_I_H
+
 #define FUSE_USE_VERSION 31
-
-
 #include "fuse.h"
 #include "fuse_lowlevel.h"
 
@@ -101,3 +102,5 @@ void fuse_session_process_buf_int(struct fuse_session *se,
 
 /* room needed in buffer to accommodate header */
 #define FUSE_BUFFER_HEADER_SIZE 0x1000
+
+#endif

tools/virtiofsd/fuse_lowlevel.c

@@ -14,6 +14,7 @@
 #include "standard-headers/linux/fuse.h"
 #include "fuse_misc.h"
 #include "fuse_opt.h"
+#include "fuse_virtio.h"
 
 #include <assert.h>
 #include <errno.h>
@@ -2202,6 +2203,11 @@ struct fuse_session *fuse_session_new(struct fuse_args *args,
         goto out4;
     }
 
+    if (!se->vu_socket_path) {
+        fprintf(stderr, "fuse: missing -o vhost_user_socket option\n");
+        goto out4;
+    }
+
     se->bufsize = FUSE_MAX_MAX_PAGES * getpagesize() + FUSE_BUFFER_HEADER_SIZE;
 
     list_init_req(&se->list);
@@ -2224,54 +2230,7 @@ out1:
 
 int fuse_session_mount(struct fuse_session *se)
 {
-    int fd;
-
-    /*
-     * Make sure file descriptors 0, 1 and 2 are open, otherwise chaos
-     * would ensue.
-     */
-    do {
-        fd = open("/dev/null", O_RDWR);
-        if (fd > 2) {
-            close(fd);
-        }
-    } while (fd >= 0 && fd <= 2);
-
-    /*
-     * To allow FUSE daemons to run without privileges, the caller may open
-     * /dev/fuse before launching the file system and pass on the file
-     * descriptor by specifying /dev/fd/N as the mount point. Note that the
-     * parent process takes care of performing the mount in this case.
-     */
-    fd = fuse_mnt_parse_fuse_fd(mountpoint);
-    if (fd != -1) {
-        if (fcntl(fd, F_GETFD) == -1) {
-            fuse_log(FUSE_LOG_ERR, "fuse: Invalid file descriptor /dev/fd/%u\n",
-                     fd);
-            return -1;
-        }
-        se->fd = fd;
-        return 0;
-    }
-
-    /* Open channel */
-    fd = fuse_kern_mount(mountpoint, se->mo);
-    if (fd == -1) {
-        return -1;
-    }
-    se->fd = fd;
-
-    /* Save mountpoint */
-    se->mountpoint = strdup(mountpoint);
-    if (se->mountpoint == NULL) {
-        goto error_out;
-    }
-
-    return 0;
-
-error_out:
-    fuse_kern_unmount(mountpoint, fd);
-    return -1;
+    return virtio_session_mount(se);
 }
 
 int fuse_session_fd(struct fuse_session *se)

tools/virtiofsd/fuse_virtio.c

@@ -0,0 +1,79 @@
+/*
+ * virtio-fs glue for FUSE
+ * Copyright (C) 2018 Red Hat, Inc. and/or its affiliates
+ *
+ * Authors:
+ *   Dave Gilbert  <dgilbert@redhat.com>
+ *
+ * Implements the glue between libfuse and libvhost-user
+ *
+ * This program can be distributed under the terms of the GNU LGPLv2.
+ * See the file COPYING.LIB
+ */
+
+#include "fuse_i.h"
+#include "standard-headers/linux/fuse.h"
+#include "fuse_misc.h"
+#include "fuse_opt.h"
+#include "fuse_virtio.h"
+
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/socket.h>
+#include <sys/types.h>
+#include <sys/un.h>
+#include <unistd.h>
+
+/* From spec */
+struct virtio_fs_config {
+    char tag[36];
+    uint32_t num_queues;
+};
+
+int virtio_session_mount(struct fuse_session *se)
+{
+    struct sockaddr_un un;
+    mode_t old_umask;
+
+    if (strlen(se->vu_socket_path) >= sizeof(un.sun_path)) {
+        fuse_log(FUSE_LOG_ERR, "Socket path too long\n");
+        return -1;
+    }
+
+    se->fd = -1;
+
+    /*
+     * Create the Unix socket to communicate with qemu
+     * based on QEMU's vhost-user-bridge
+     */
+    unlink(se->vu_socket_path);
+    strcpy(un.sun_path, se->vu_socket_path);
+    size_t addr_len = sizeof(un);
+
+    int listen_sock = socket(AF_UNIX, SOCK_STREAM, 0);
+    if (listen_sock == -1) {
+        fuse_log(FUSE_LOG_ERR, "vhost socket creation: %m\n");
+        return -1;
+    }
+    un.sun_family = AF_UNIX;
+
+    /*
+     * Unfortunately bind doesn't let you set the mask on the socket,
+     * so set umask to 077 and restore it later.
+     */
+    old_umask = umask(0077);
+    if (bind(listen_sock, (struct sockaddr *)&un, addr_len) == -1) {
+        fuse_log(FUSE_LOG_ERR, "vhost socket bind: %m\n");
+        umask(old_umask);
+        return -1;
+    }
+    umask(old_umask);
+
+    if (listen(listen_sock, 1) == -1) {
+        fuse_log(FUSE_LOG_ERR, "vhost socket listen: %m\n");
+        return -1;
+    }
+
+    return -1;
+}

tools/virtiofsd/fuse_virtio.h

@@ -0,0 +1,23 @@
+/*
+ * virtio-fs glue for FUSE
+ * Copyright (C) 2018 Red Hat, Inc. and/or its affiliates
+ *
+ * Authors:
+ *   Dave Gilbert  <dgilbert@redhat.com>
+ *
+ * Implements the glue between libfuse and libvhost-user
+ *
+ * This program can be distributed under the terms of the GNU LGPLv2.
+ *  See the file COPYING.LIB
+ */
+
+#ifndef FUSE_VIRTIO_H
+#define FUSE_VIRTIO_H
+
+#include "fuse_i.h"
+
+struct fuse_session;
+
+int virtio_session_mount(struct fuse_session *se);
+
+#endif