[Qemu-devel] [RFC PATCH 2/7] virtio: add vhost-user-fs-pci device

[Dr. David Alan Gilbert (git)]

From: Stefan Hajnoczi <address@hidden>

The virtio-fs virtio device provides shared file system access.  The
actual file server is implemented in an external vhost-user-fs device
backend process.

Launch QEMU like this:

  qemu -chardev socket,path=/tmp/vhost-fs.sock,id=chr0
       -device vhost-user-fs-pci,tag=myfs,chardev=chr0

Signed-off-by: Stefan Hajnoczi <address@hidden>
---
 configure                                   |  10 +
 hw/virtio/Makefile.objs                     |   1 +
 hw/virtio/vhost-user-fs.c                   | 297 ++++++++++++++++++++
 hw/virtio/virtio-pci.c                      |  52 ++++
 hw/virtio/virtio-pci.h                      |  18 ++
 include/hw/pci/pci.h                        |   1 +
 include/hw/virtio/vhost-user-fs.h           |  45 +++
 include/standard-headers/linux/virtio_fs.h  |  41 +++
 include/standard-headers/linux/virtio_ids.h |   1 +
 9 files changed, 466 insertions(+)
 create mode 100644 hw/virtio/vhost-user-fs.c
 create mode 100644 include/hw/virtio/vhost-user-fs.h
 create mode 100644 include/standard-headers/linux/virtio_fs.h

diff --git a/configure b/configure
index 0a3c6a72c3..140b89d8f0 100755
--- a/configure
+++ b/configure
@@ -371,6 +371,7 @@ vhost_crypto="no"
 vhost_scsi="no"
 vhost_vsock="no"
 vhost_user=""
+vhost_user_fs="no"
 kvm="no"
 hax="no"
 hvf="no"
@@ -878,6 +879,7 @@ Linux)
   vhost_crypto="yes"
   vhost_scsi="yes"
   vhost_vsock="yes"
+  vhost_user_fs="yes"
   QEMU_INCLUDES="-I\$(SRC_PATH)/linux-headers -I$PWD/linux-headers 
$QEMU_INCLUDES"
   supported_os="yes"
   libudev="yes"
@@ -1272,6 +1274,10 @@ for opt do
   ;;
   --enable-vhost-vsock) vhost_vsock="yes"
   ;;
+  --disable-vhost-user-fs) vhost_user_fs="no"
+  ;;
+  --enable-vhost-user-fs) vhost_user_fs="yes"
+  ;;
   --disable-opengl) opengl="no"
   ;;
   --enable-opengl) opengl="yes"
@@ -6054,6 +6060,7 @@ echo "vhost-crypto support $vhost_crypto"
 echo "vhost-scsi support $vhost_scsi"
 echo "vhost-vsock support $vhost_vsock"
 echo "vhost-user support $vhost_user"
+echo "vhost-user-fs support $vhost_user_fs"
 echo "Trace backends    $trace_backends"
 if have_backend "simple"; then
 echo "Trace output file $trace_file-<pid>"
@@ -6524,6 +6531,9 @@ fi
 if test "$vhost_user" = "yes" ; then
   echo "CONFIG_VHOST_USER=y" >> $config_host_mak
 fi
+if test "$vhost_user_fs" = "yes" ; then
+  echo "CONFIG_VHOST_USER_FS=y" >> $config_host_mak
+fi
 if test "$blobs" = "yes" ; then
   echo "INSTALL_BLOBS=yes" >> $config_host_mak
 fi
diff --git a/hw/virtio/Makefile.objs b/hw/virtio/Makefile.objs
index 1b2799cfd8..6783932231 100644
--- a/hw/virtio/Makefile.objs
+++ b/hw/virtio/Makefile.objs
@@ -11,6 +11,7 @@ obj-$(call land,$(CONFIG_VIRTIO_CRYPTO),$(CONFIG_VIRTIO_PCI)) 
+= virtio-crypto-p
 
 obj-$(CONFIG_LINUX) += vhost.o vhost-backend.o vhost-user.o
 obj-$(CONFIG_VHOST_VSOCK) += vhost-vsock.o
+obj-$(CONFIG_VHOST_USER_FS) += vhost-user-fs.o
 endif
 
 common-obj-$(call lnot,$(call land,$(CONFIG_VIRTIO),$(CONFIG_LINUX))) += 
vhost-stub.o
diff --git a/hw/virtio/vhost-user-fs.c b/hw/virtio/vhost-user-fs.c
new file mode 100644
index 0000000000..bc21beeac3
--- /dev/null
+++ b/hw/virtio/vhost-user-fs.c
@@ -0,0 +1,297 @@
+/*
+ * Vhost-user filesystem virtio device
+ *
+ * Copyright 2018 Red Hat, Inc.
+ *
+ * Authors:
+ *  Stefan Hajnoczi <address@hidden>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or
+ * (at your option) any later version.  See the COPYING file in the
+ * top-level directory.
+ */
+
+#include "qemu/osdep.h"
+#include <sys/ioctl.h>
+#include "standard-headers/linux/virtio_fs.h"
+#include "qapi/error.h"
+#include "hw/virtio/virtio-bus.h"
+#include "hw/virtio/virtio-access.h"
+#include "qemu/error-report.h"
+#include "hw/virtio/vhost-user-fs.h"
+#include "monitor/monitor.h"
+
+static void vuf_get_config(VirtIODevice *vdev, uint8_t *config)
+{
+    VHostUserFS *fs = VHOST_USER_FS(vdev);
+    struct virtio_fs_config fscfg = {};
+
+    /* strncpy(3) is okay, the field is not NUL-terminated at max size */
+    strncpy((char *)fscfg.tag, fs->conf.tag, sizeof(fscfg.tag));
+
+    virtio_stl_p(vdev, &fscfg.num_queues, fs->conf.num_queues);
+
+    memcpy(config, &fscfg, sizeof(fscfg));
+}
+
+static void vuf_start(VirtIODevice *vdev)
+{
+    VHostUserFS *fs = VHOST_USER_FS(vdev);
+    BusState *qbus = BUS(qdev_get_parent_bus(DEVICE(vdev)));
+    VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(qbus);
+    int ret;
+    int i;
+
+    if (!k->set_guest_notifiers) {
+        error_report("binding does not support guest notifiers");
+        return;
+    }
+
+    ret = vhost_dev_enable_notifiers(&fs->vhost_dev, vdev);
+    if (ret < 0) {
+        error_report("Error enabling host notifiers: %d", -ret);
+        return;
+    }
+
+    ret = k->set_guest_notifiers(qbus->parent, fs->vhost_dev.nvqs, true);
+    if (ret < 0) {
+        error_report("Error binding guest notifier: %d", -ret);
+        goto err_host_notifiers;
+    }
+
+    fs->vhost_dev.acked_features = vdev->guest_features;
+    ret = vhost_dev_start(&fs->vhost_dev, vdev);
+    if (ret < 0) {
+        error_report("Error starting vhost: %d", -ret);
+        goto err_guest_notifiers;
+    }
+
+    /* guest_notifier_mask/pending not used yet, so just unmask
+     * everything here.  virtio-pci will do the right thing by
+     * enabling/disabling irqfd.
+     */
+    for (i = 0; i < fs->vhost_dev.nvqs; i++) {
+        vhost_virtqueue_mask(&fs->vhost_dev, vdev, i, false);
+    }
+
+    return;
+
+err_guest_notifiers:
+    k->set_guest_notifiers(qbus->parent, fs->vhost_dev.nvqs, false);
+err_host_notifiers:
+    vhost_dev_disable_notifiers(&fs->vhost_dev, vdev);
+}
+
+static void vuf_stop(VirtIODevice *vdev)
+{
+    VHostUserFS *fs = VHOST_USER_FS(vdev);
+    BusState *qbus = BUS(qdev_get_parent_bus(DEVICE(vdev)));
+    VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(qbus);
+    int ret;
+
+    if (!k->set_guest_notifiers) {
+        return;
+    }
+
+    vhost_dev_stop(&fs->vhost_dev, vdev);
+
+    ret = k->set_guest_notifiers(qbus->parent, fs->vhost_dev.nvqs, false);
+    if (ret < 0) {
+        error_report("vhost guest notifier cleanup failed: %d", ret);
+        return;
+    }
+
+    vhost_dev_disable_notifiers(&fs->vhost_dev, vdev);
+}
+
+static void vuf_set_status(VirtIODevice *vdev, uint8_t status)
+{
+    VHostUserFS *fs = VHOST_USER_FS(vdev);
+    bool should_start = status & VIRTIO_CONFIG_S_DRIVER_OK;
+
+    if (!vdev->vm_running) {
+        should_start = false;
+    }
+
+    if (fs->vhost_dev.started == should_start) {
+        return;
+    }
+
+    if (should_start) {
+        vuf_start(vdev);
+    } else {
+        vuf_stop(vdev);
+    }
+}
+
+static uint64_t vuf_get_features(VirtIODevice *vdev,
+                                      uint64_t requested_features,
+                                      Error **errp)
+{
+    /* No feature bits used yet */
+    return requested_features;
+}
+
+static void vuf_handle_output(VirtIODevice *vdev, VirtQueue *vq)
+{
+    /* Do nothing */
+}
+
+static void vuf_guest_notifier_mask(VirtIODevice *vdev, int idx,
+                                            bool mask)
+{
+    VHostUserFS *fs = VHOST_USER_FS(vdev);
+
+    vhost_virtqueue_mask(&fs->vhost_dev, vdev, idx, mask);
+}
+
+static bool vuf_guest_notifier_pending(VirtIODevice *vdev, int idx)
+{
+    VHostUserFS *fs = VHOST_USER_FS(vdev);
+
+    return vhost_virtqueue_pending(&fs->vhost_dev, idx);
+}
+
+static void vuf_device_realize(DeviceState *dev, Error **errp)
+{
+    VirtIODevice *vdev = VIRTIO_DEVICE(dev);
+    VHostUserFS *fs = VHOST_USER_FS(dev);
+    unsigned int i;
+    size_t len;
+    int ret;
+
+    if (!fs->conf.chardev.chr) {
+        error_setg(errp, "missing chardev");
+        return;
+    }
+
+    if (!fs->conf.tag) {
+        error_setg(errp, "missing tag property");
+        return;
+    }
+    len = strlen(fs->conf.tag);
+    if (len == 0) {
+        error_setg(errp, "tag property cannot be empty");
+        return;
+    }
+    if (len > sizeof_field(struct virtio_fs_config, tag)) {
+        error_setg(errp, "tag property must be %zu bytes or less",
+                   sizeof_field(struct virtio_fs_config, tag));
+        return;
+    }
+
+    if (fs->conf.num_queues == 0) {
+        error_setg(errp, "num-queues property must be larger than 0");
+        return;
+    }
+
+    if (!is_power_of_2(fs->conf.queue_size)) {
+        error_setg(errp, "queue-size property must be a power of 2");
+        return;
+    }
+
+    if (fs->conf.queue_size > VIRTQUEUE_MAX_SIZE) {
+        error_setg(errp, "queue-size property must be %u or smaller",
+                   VIRTQUEUE_MAX_SIZE);
+        return;
+    }
+
+    fs->vhost_user = vhost_user_init();
+    if (!fs->vhost_user) {
+        error_setg(errp, "failed to initialize vhost-user");
+        return;
+    }
+    fs->vhost_user->chr = &fs->conf.chardev;
+
+    virtio_init(vdev, "vhost-user-fs", VIRTIO_ID_FS,
+                sizeof(struct virtio_fs_config));
+
+    /* Notifications queue */
+    virtio_add_queue(vdev, fs->conf.queue_size, vuf_handle_output);
+
+    /* Hiprio queue */
+    virtio_add_queue(vdev, fs->conf.queue_size, vuf_handle_output);
+
+    /* Request queues */
+    for (i = 0; i < fs->conf.num_queues; i++) {
+        virtio_add_queue(vdev, fs->conf.queue_size, vuf_handle_output);
+    }
+
+    fs->vhost_dev.nvqs = 2 + fs->conf.num_queues;
+    fs->vhost_dev.vqs = g_new0(struct vhost_virtqueue, fs->vhost_dev.nvqs);
+    ret = vhost_dev_init(&fs->vhost_dev, fs->vhost_user,
+                         VHOST_BACKEND_TYPE_USER, 0);
+    if (ret < 0) {
+        error_setg_errno(errp, -ret, "vhost_dev_init failed");
+        goto err_virtio;
+    }
+
+    return;
+
+err_virtio:
+    vhost_user_cleanup(fs->vhost_user);
+    g_free(fs->vhost_user);
+    virtio_cleanup(vdev);
+    g_free(fs->vhost_dev.vqs);
+    return;
+}
+
+static void vuf_device_unrealize(DeviceState *dev, Error **errp)
+{
+    VirtIODevice *vdev = VIRTIO_DEVICE(dev);
+    VHostUserFS *fs = VHOST_USER_FS(dev);
+
+    /* This will stop vhost backend if appropriate. */
+    vuf_set_status(vdev, 0);
+
+    vhost_dev_cleanup(&fs->vhost_dev);
+
+    if (fs->vhost_user) {
+        vhost_user_cleanup(fs->vhost_user);
+        g_free(fs->vhost_user);
+        fs->vhost_user = NULL;
+    }
+
+    virtio_cleanup(vdev);
+    g_free(fs->vhost_dev.vqs);
+    fs->vhost_dev.vqs = NULL;
+}
+
+static Property vuf_properties[] = {
+    DEFINE_PROP_CHR("chardev", VHostUserFS, conf.chardev),
+    DEFINE_PROP_STRING("tag", VHostUserFS, conf.tag),
+    DEFINE_PROP_UINT16("num-queues", VHostUserFS, conf.num_queues, 1),
+    DEFINE_PROP_UINT16("queue-size", VHostUserFS, conf.queue_size, 128),
+    DEFINE_PROP_STRING("vhostfd", VHostUserFS, conf.vhostfd),
+    DEFINE_PROP_END_OF_LIST(),
+};
+
+static void vuf_class_init(ObjectClass *klass, void *data)
+{
+    DeviceClass *dc = DEVICE_CLASS(klass);
+    VirtioDeviceClass *vdc = VIRTIO_DEVICE_CLASS(klass);
+
+    dc->props = vuf_properties;
+    set_bit(DEVICE_CATEGORY_STORAGE, dc->categories);
+    vdc->realize = vuf_device_realize;
+    vdc->unrealize = vuf_device_unrealize;
+    vdc->get_features = vuf_get_features;
+    vdc->get_config = vuf_get_config;
+    vdc->set_status = vuf_set_status;
+    vdc->guest_notifier_mask = vuf_guest_notifier_mask;
+    vdc->guest_notifier_pending = vuf_guest_notifier_pending;
+}
+
+static const TypeInfo vuf_info = {
+    .name = TYPE_VHOST_USER_FS,
+    .parent = TYPE_VIRTIO_DEVICE,
+    .instance_size = sizeof(VHostUserFS),
+    .class_init = vuf_class_init,
+};
+
+static void vuf_register_types(void)
+{
+    type_register_static(&vuf_info);
+}
+
+type_init(vuf_register_types)
diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
index 1e737531b5..d744f93655 100644
--- a/hw/virtio/virtio-pci.c
+++ b/hw/virtio/virtio-pci.c
@@ -2665,6 +2665,55 @@ static const TypeInfo virtio_host_pci_info = {
 };
 #endif
 
+/* vhost-user-fs-pci */
+
+#ifdef CONFIG_VHOST_USER_FS
+static Property vhost_user_fs_pci_properties[] = {
+    /* TODO multiqueue */
+    DEFINE_PROP_UINT32("vectors", VirtIOPCIProxy, nvectors, 4),
+    DEFINE_PROP_END_OF_LIST(),
+};
+
+static void vhost_user_fs_pci_realize(VirtIOPCIProxy *vpci_dev, Error **errp)
+{
+    VHostUserFSPCI *dev = VHOST_USER_FS_PCI(vpci_dev);
+    DeviceState *vdev = DEVICE(&dev->vdev);
+
+    qdev_set_parent_bus(vdev, BUS(&vpci_dev->bus));
+    object_property_set_bool(OBJECT(vdev), true, "realized", errp);
+}
+
+static void vhost_user_fs_pci_class_init(ObjectClass *klass, void *data)
+{
+    DeviceClass *dc = DEVICE_CLASS(klass);
+    VirtioPCIClass *k = VIRTIO_PCI_CLASS(klass);
+    PCIDeviceClass *pcidev_k = PCI_DEVICE_CLASS(klass);
+    k->realize = vhost_user_fs_pci_realize;
+    set_bit(DEVICE_CATEGORY_STORAGE, dc->categories);
+    dc->props = vhost_user_fs_pci_properties;
+    pcidev_k->vendor_id = PCI_VENDOR_ID_REDHAT_QUMRANET;
+    pcidev_k->device_id = PCI_DEVICE_ID_VIRTIO_FS;
+    pcidev_k->revision = 0x00;
+    pcidev_k->class_id = PCI_CLASS_STORAGE_OTHER;
+}
+
+static void vhost_user_fs_pci_instance_init(Object *obj)
+{
+    VHostUserFSPCI *dev = VHOST_USER_FS_PCI(obj);
+
+    virtio_instance_init_common(obj, &dev->vdev, sizeof(dev->vdev),
+                                TYPE_VHOST_USER_FS);
+}
+
+static const TypeInfo vhost_user_fs_pci_info = {
+    .name          = TYPE_VHOST_USER_FS_PCI,
+    .parent        = TYPE_VIRTIO_PCI,
+    .instance_size = sizeof(VHostUserFSPCI),
+    .instance_init = vhost_user_fs_pci_instance_init,
+    .class_init    = vhost_user_fs_pci_class_init,
+};
+#endif
+
 /* virtio-pci-bus */
 
 static void virtio_pci_bus_new(VirtioBusState *bus, size_t bus_size,
@@ -2743,6 +2792,9 @@ static void virtio_pci_register_types(void)
 #ifdef CONFIG_VHOST_VSOCK
     type_register_static(&vhost_vsock_pci_info);
 #endif
+#ifdef CONFIG_VHOST_USER_FS
+    type_register_static(&vhost_user_fs_pci_info);
+#endif
 }
 
 type_init(virtio_pci_register_types)
diff --git a/hw/virtio/virtio-pci.h b/hw/virtio/virtio-pci.h
index 813082b0d7..a635dc564c 100644
--- a/hw/virtio/virtio-pci.h
+++ b/hw/virtio/virtio-pci.h
@@ -40,6 +40,9 @@
 #ifdef CONFIG_VHOST_VSOCK
 #include "hw/virtio/vhost-vsock.h"
 #endif
+#ifdef CONFIG_VHOST_USER_FS
+#include "hw/virtio/vhost-user-fs.h"
+#endif
 
 typedef struct VirtIOPCIProxy VirtIOPCIProxy;
 typedef struct VirtIOBlkPCI VirtIOBlkPCI;
@@ -57,6 +60,7 @@ typedef struct VirtIOInputHostPCI VirtIOInputHostPCI;
 typedef struct VirtIOGPUPCI VirtIOGPUPCI;
 typedef struct VHostVSockPCI VHostVSockPCI;
 typedef struct VirtIOCryptoPCI VirtIOCryptoPCI;
+typedef struct VHostUserFSPCI VHostUserFSPCI;
 
 /* virtio-pci-bus */
 
@@ -414,6 +418,20 @@ struct VirtIOCryptoPCI {
     VirtIOCrypto vdev;
 };
 
+#ifdef CONFIG_VHOST_USER_FS
+/*
+ * vhost-user-fs-pci: This extends VirtioPCIProxy.
+ */
+#define TYPE_VHOST_USER_FS_PCI "vhost-user-fs-pci"
+#define VHOST_USER_FS_PCI(obj) \
+        OBJECT_CHECK(VHostUserFSPCI, (obj), TYPE_VHOST_USER_FS_PCI)
+
+struct VHostUserFSPCI {
+    VirtIOPCIProxy parent_obj;
+    VHostUserFS vdev;
+};
+#endif
+
 /* Virtio ABI version, if we increment this, we break the guest driver. */
 #define VIRTIO_PCI_ABI_VERSION          0
 
diff --git a/include/hw/pci/pci.h b/include/hw/pci/pci.h
index e6514bba23..2adc3bf45f 100644
--- a/include/hw/pci/pci.h
+++ b/include/hw/pci/pci.h
@@ -85,6 +85,7 @@ extern bool pci_available;
 #define PCI_DEVICE_ID_VIRTIO_RNG         0x1005
 #define PCI_DEVICE_ID_VIRTIO_9P          0x1009
 #define PCI_DEVICE_ID_VIRTIO_VSOCK       0x1012
+#define PCI_DEVICE_ID_VIRTIO_FS          0x1019
 
 #define PCI_VENDOR_ID_REDHAT             0x1b36
 #define PCI_DEVICE_ID_REDHAT_BRIDGE      0x0001
diff --git a/include/hw/virtio/vhost-user-fs.h 
b/include/hw/virtio/vhost-user-fs.h
new file mode 100644
index 0000000000..29629acc54
--- /dev/null
+++ b/include/hw/virtio/vhost-user-fs.h
@@ -0,0 +1,45 @@
+/*
+ * Vhost-user filesystem virtio device
+ *
+ * Copyright 2018 Red Hat, Inc.
+ *
+ * Authors:
+ *  Stefan Hajnoczi <address@hidden>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or
+ * (at your option) any later version.  See the COPYING file in the
+ * top-level directory.
+ */
+
+#ifndef _QEMU_VHOST_USER_FS_H
+#define _QEMU_VHOST_USER_FS_H
+
+#include "hw/virtio/virtio.h"
+#include "hw/virtio/vhost.h"
+#include "hw/virtio/vhost-user.h"
+#include "chardev/char-fe.h"
+
+#define TYPE_VHOST_USER_FS "vhost-user-fs-device"
+#define VHOST_USER_FS(obj) \
+        OBJECT_CHECK(VHostUserFS, (obj), TYPE_VHOST_USER_FS)
+
+typedef struct {
+    CharBackend chardev;
+    char *tag;
+    uint16_t num_queues;
+    uint16_t queue_size;
+    char *vhostfd;
+} VHostUserFSConf;
+
+typedef struct {
+    /*< private >*/
+    VirtIODevice parent;
+    VHostUserFSConf conf;
+    struct vhost_virtqueue *vhost_vqs;
+    struct vhost_dev vhost_dev;
+    VhostUserState *vhost_user;
+
+    /*< public >*/
+} VHostUserFS;
+
+#endif /* _QEMU_VHOST_USER_FS_H */
diff --git a/include/standard-headers/linux/virtio_fs.h 
b/include/standard-headers/linux/virtio_fs.h
new file mode 100644
index 0000000000..4f811a0b70
--- /dev/null
+++ b/include/standard-headers/linux/virtio_fs.h
@@ -0,0 +1,41 @@
+#ifndef _LINUX_VIRTIO_FS_H
+#define _LINUX_VIRTIO_FS_H
+/* This header is BSD licensed so anyone can use the definitions to implement
+ * compatible drivers/servers.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of IBM nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ``AS 
IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL IBM OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE. */
+#include "standard-headers/linux/types.h"
+#include "standard-headers/linux/virtio_ids.h"
+#include "standard-headers/linux/virtio_config.h"
+#include "standard-headers/linux/virtio_types.h"
+
+struct virtio_fs_config {
+       /* Filesystem name (UTF-8, not NUL-terminated, padded with NULs) */
+       uint8_t tag[36];
+
+       /* Number of request queues */
+       uint32_t num_queues;
+} QEMU_PACKED;
+
+#endif /* _LINUX_VIRTIO_FS_H */
diff --git a/include/standard-headers/linux/virtio_ids.h 
b/include/standard-headers/linux/virtio_ids.h
index 6d5c3b2d4f..884b0e2734 100644
--- a/include/standard-headers/linux/virtio_ids.h
+++ b/include/standard-headers/linux/virtio_ids.h
@@ -43,5 +43,6 @@
 #define VIRTIO_ID_INPUT        18 /* virtio input */
 #define VIRTIO_ID_VSOCK        19 /* virtio vsock transport */
 #define VIRTIO_ID_CRYPTO       20 /* virtio crypto */
+#define VIRTIO_ID_FS           26 /* virtio filesystem */
 
 #endif /* _LINUX_VIRTIO_IDS_H */
-- 
2.19.2