Introduce Virtio-loopback epsilon release:

Epsilon release introduces a new compatibility layer which make virtio-loopback
design to work with QEMU and rust-vmm vhost-user backend without require any
changes.

Signed-off-by: Timos Ampelikiotis <t.ampelikiotis@virtualopensystems.com>
Change-Id: I52e57563e08a7d0bdc002f8e928ee61ba0c53dd9

1 files changed, 1079 insertions, 0 deletions

diff --git a/tools/virtiofsd/fuse_virtio.c b/tools/virtiofsd/fuse_virtio.c
new file mode 100644
index 000000000..60b96470c
--- /dev/null
+++ b/tools/virtiofsd/fuse_virtio.c
@@ -0,0 +1,1079 @@
+/*
+ * 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 "qemu/osdep.h"
+#include "qemu/iov.h"
+#include "qapi/error.h"
+#include "fuse_i.h"
+#include "standard-headers/linux/fuse.h"
+#include "fuse_misc.h"
+#include "fuse_opt.h"
+#include "fuse_virtio.h"
+
+#include <sys/eventfd.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <grp.h>
+
+#include "libvhost-user.h"
+
+struct fv_VuDev;
+struct fv_QueueInfo {
+    pthread_t thread;
+    /*
+     * This lock protects the VuVirtq preventing races between
+     * fv_queue_thread() and fv_queue_worker().
+     */
+    pthread_mutex_t vq_lock;
+
+    struct fv_VuDev *virtio_dev;
+
+    /* Our queue index, corresponds to array position */
+    int qidx;
+    int kick_fd;
+    int kill_fd; /* For killing the thread */
+};
+
+/* A FUSE request */
+typedef struct {
+    VuVirtqElement elem;
+    struct fuse_chan ch;
+
+    /* Used to complete requests that involve no reply */
+    bool reply_sent;
+} FVRequest;
+
+/*
+ * 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;
+
+    /*
+     * Either handle virtqueues or vhost-user protocol messages.  Don't do
+     * both at the same time since that could lead to race conditions if
+     * virtqueues or memory tables change while another thread is accessing
+     * them.
+     *
+     * The assumptions are:
+     * 1. fv_queue_thread() reads/writes to virtqueues and only reads VuDev.
+     * 2. virtio_loop() reads/writes virtqueues and VuDev.
+     */
+    pthread_rwlock_t vu_dispatch_rwlock;
+
+    /*
+     * The following pair of fields are only accessed in the main
+     * virtio_loop
+     */
+    size_t nqueues;
+    struct fv_QueueInfo **qi;
+};
+
+/* Callback from libvhost-user */
+static uint64_t fv_get_features(VuDev *dev)
+{
+    return 1ULL << VIRTIO_F_VERSION_1;
+}
+
+/* Callback from libvhost-user */
+static void fv_set_features(VuDev *dev, uint64_t features)
+{
+}
+
+/*
+ * 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);
+}
+
+/*
+ * Copy from an iovec into a fuse_buf (memory only)
+ * Caller must ensure there is space
+ */
+static size_t copy_from_iov(struct fuse_buf *buf, size_t out_num,
+                            const struct iovec *out_sg,
+                            size_t max)
+{
+    void *dest = buf->mem;
+    size_t copied = 0;
+
+    while (out_num && max) {
+        size_t onelen = out_sg->iov_len;
+        onelen = MIN(onelen, max);
+        memcpy(dest, out_sg->iov_base, onelen);
+        dest += onelen;
+        copied += onelen;
+        out_sg++;
+        out_num--;
+        max -= onelen;
+    }
+
+    return copied;
+}
+
+/*
+ * Skip 'skip' bytes in the iov; 'sg_1stindex' is set as
+ * the index for the 1st iovec to read data from, and
+ * 'sg_1stskip' is the number of bytes to skip in that entry.
+ *
+ * Returns True if there are at least 'skip' bytes in the iovec
+ *
+ */
+static bool skip_iov(const struct iovec *sg, size_t sg_size,
+                     size_t skip,
+                     size_t *sg_1stindex, size_t *sg_1stskip)
+{
+    size_t vec;
+
+    for (vec = 0; vec < sg_size; vec++) {
+        if (sg[vec].iov_len > skip) {
+            *sg_1stskip = skip;
+            *sg_1stindex = vec;
+
+            return true;
+        }
+
+        skip -= sg[vec].iov_len;
+    }
+
+    *sg_1stindex = vec;
+    *sg_1stskip = 0;
+    return skip == 0;
+}
+
+/*
+ * Copy from one iov to another, the given number of bytes
+ * The caller must have checked sizes.
+ */
+static void copy_iov(struct iovec *src_iov, int src_count,
+                     struct iovec *dst_iov, int dst_count, size_t to_copy)
+{
+    size_t dst_offset = 0;
+    /* Outer loop copies 'src' elements */
+    while (to_copy) {
+        assert(src_count);
+        size_t src_len = src_iov[0].iov_len;
+        size_t src_offset = 0;
+
+        if (src_len > to_copy) {
+            src_len = to_copy;
+        }
+        /* Inner loop copies contents of one 'src' to maybe multiple dst. */
+        while (src_len) {
+            assert(dst_count);
+            size_t dst_len = dst_iov[0].iov_len - dst_offset;
+            if (dst_len > src_len) {
+                dst_len = src_len;
+            }
+
+            memcpy(dst_iov[0].iov_base + dst_offset,
+                   src_iov[0].iov_base + src_offset, dst_len);
+            src_len -= dst_len;
+            to_copy -= dst_len;
+            src_offset += dst_len;
+            dst_offset += dst_len;
+
+            assert(dst_offset <= dst_iov[0].iov_len);
+            if (dst_offset == dst_iov[0].iov_len) {
+                dst_offset = 0;
+                dst_iov++;
+                dst_count--;
+            }
+        }
+        src_iov++;
+        src_count--;
+    }
+}
+
+/*
+ * pthread_rwlock_rdlock() and pthread_rwlock_wrlock can fail if
+ * a deadlock condition is detected or the current thread already
+ * owns the lock. They can also fail, like pthread_rwlock_unlock(),
+ * if the mutex wasn't properly initialized. None of these are ever
+ * expected to happen.
+ */
+static void vu_dispatch_rdlock(struct fv_VuDev *vud)
+{
+    int ret = pthread_rwlock_rdlock(&vud->vu_dispatch_rwlock);
+    assert(ret == 0);
+}
+
+static void vu_dispatch_wrlock(struct fv_VuDev *vud)
+{
+    int ret = pthread_rwlock_wrlock(&vud->vu_dispatch_rwlock);
+    assert(ret == 0);
+}
+
+static void vu_dispatch_unlock(struct fv_VuDev *vud)
+{
+    int ret = pthread_rwlock_unlock(&vud->vu_dispatch_rwlock);
+    assert(ret == 0);
+}
+
+static void vq_send_element(struct fv_QueueInfo *qi, VuVirtqElement *elem,
+                            ssize_t len)
+{
+    struct fuse_session *se = qi->virtio_dev->se;
+    VuDev *dev = &se->virtio_dev->dev;
+    VuVirtq *q = vu_get_queue(dev, qi->qidx);
+
+    vu_dispatch_rdlock(qi->virtio_dev);
+    pthread_mutex_lock(&qi->vq_lock);
+    vu_queue_push(dev, q, elem, len);
+    vu_queue_notify(dev, q);
+    pthread_mutex_unlock(&qi->vq_lock);
+    vu_dispatch_unlock(qi->virtio_dev);
+}
+
+/*
+ * Called back by ll whenever it wants to send a reply/message back
+ * The 1st element of the iov starts with the fuse_out_header
+ * 'unique'==0 means it's a notify message.
+ */
+int virtio_send_msg(struct fuse_session *se, struct fuse_chan *ch,
+                    struct iovec *iov, int count)
+{
+    FVRequest *req = container_of(ch, FVRequest, ch);
+    struct fv_QueueInfo *qi = ch->qi;
+    VuVirtqElement *elem = &req->elem;
+    int ret = 0;
+
+    assert(count >= 1);
+    assert(iov[0].iov_len >= sizeof(struct fuse_out_header));
+
+    struct fuse_out_header *out = iov[0].iov_base;
+    /* TODO: Endianness! */
+
+    size_t tosend_len = iov_size(iov, count);
+
+    /* unique == 0 is notification, which we don't support */
+    assert(out->unique);
+    assert(!req->reply_sent);
+
+    /* The 'in' part of the elem is to qemu */
+    unsigned int in_num = elem->in_num;
+    struct iovec *in_sg = elem->in_sg;
+    size_t in_len = iov_size(in_sg, in_num);
+    fuse_log(FUSE_LOG_DEBUG, "%s: elem %d: with %d in desc of length %zd\n",
+             __func__, elem->index, in_num, in_len);
+
+    /*
+     * The elem should have room for a 'fuse_out_header' (out from fuse)
+     * plus the data based on the len in the header.
+     */
+    if (in_len < sizeof(struct fuse_out_header)) {
+        fuse_log(FUSE_LOG_ERR, "%s: elem %d too short for out_header\n",
+                 __func__, elem->index);
+        ret = -E2BIG;
+        goto err;
+    }
+    if (in_len < tosend_len) {
+        fuse_log(FUSE_LOG_ERR, "%s: elem %d too small for data len %zd\n",
+                 __func__, elem->index, tosend_len);
+        ret = -E2BIG;
+        goto err;
+    }
+
+    copy_iov(iov, count, in_sg, in_num, tosend_len);
+
+    vq_send_element(qi, elem, tosend_len);
+    req->reply_sent = true;
+
+err:
+    return ret;
+}
+
+/*
+ * Callback from fuse_send_data_iov_* when it's virtio and the buffer
+ * is a single FD with FUSE_BUF_IS_FD | FUSE_BUF_FD_SEEK
+ * We need send the iov and then the buffer.
+ * Return 0 on success
+ */
+int virtio_send_data_iov(struct fuse_session *se, struct fuse_chan *ch,
+                         struct iovec *iov, int count, struct fuse_bufvec *buf,
+                         size_t len)
+{
+    FVRequest *req = container_of(ch, FVRequest, ch);
+    struct fv_QueueInfo *qi = ch->qi;
+    VuVirtqElement *elem = &req->elem;
+    int ret = 0;
+    g_autofree struct iovec *in_sg_cpy = NULL;
+
+    assert(count >= 1);
+    assert(iov[0].iov_len >= sizeof(struct fuse_out_header));
+
+    struct fuse_out_header *out = iov[0].iov_base;
+    /* TODO: Endianness! */
+
+    size_t iov_len = iov_size(iov, count);
+    size_t tosend_len = iov_len + len;
+
+    out->len = tosend_len;
+
+    fuse_log(FUSE_LOG_DEBUG, "%s: count=%d len=%zd iov_len=%zd\n", __func__,
+             count, len, iov_len);
+
+    /* unique == 0 is notification which we don't support */
+    assert(out->unique);
+
+    assert(!req->reply_sent);
+
+    /* The 'in' part of the elem is to qemu */
+    unsigned int in_num = elem->in_num;
+    struct iovec *in_sg = elem->in_sg;
+    size_t in_len = iov_size(in_sg, in_num);
+    fuse_log(FUSE_LOG_DEBUG, "%s: elem %d: with %d in desc of length %zd\n",
+             __func__, elem->index, in_num, in_len);
+
+    /*
+     * The elem should have room for a 'fuse_out_header' (out from fuse)
+     * plus the data based on the len in the header.
+     */
+    if (in_len < sizeof(struct fuse_out_header)) {
+        fuse_log(FUSE_LOG_ERR, "%s: elem %d too short for out_header\n",
+                 __func__, elem->index);
+        return E2BIG;
+    }
+    if (in_len < tosend_len) {
+        fuse_log(FUSE_LOG_ERR, "%s: elem %d too small for data len %zd\n",
+                 __func__, elem->index, tosend_len);
+        return E2BIG;
+    }
+
+    /* TODO: Limit to 'len' */
+
+    /* First copy the header data from iov->in_sg */
+    copy_iov(iov, count, in_sg, in_num, iov_len);
+
+    /*
+     * Build a copy of the the in_sg iov so we can skip bits in it,
+     * including changing the offsets
+     */
+    in_sg_cpy = g_new(struct iovec, in_num);
+    memcpy(in_sg_cpy, in_sg, sizeof(struct iovec) * in_num);
+    /* These get updated as we skip */
+    struct iovec *in_sg_ptr = in_sg_cpy;
+    unsigned int in_sg_cpy_count = in_num;
+
+    /* skip over parts of in_sg that contained the header iov */
+    iov_discard_front(&in_sg_ptr, &in_sg_cpy_count, iov_len);
+
+    do {
+        fuse_log(FUSE_LOG_DEBUG, "%s: in_sg_cpy_count=%d len remaining=%zd\n",
+                 __func__, in_sg_cpy_count, len);
+
+        ret = preadv(buf->buf[0].fd, in_sg_ptr, in_sg_cpy_count,
+                     buf->buf[0].pos);
+
+        if (ret == -1) {
+            ret = errno;
+            if (ret == EINTR) {
+                continue;
+            }
+            fuse_log(FUSE_LOG_DEBUG, "%s: preadv failed (%m) len=%zd\n",
+                     __func__, len);
+            return ret;
+        }
+
+        if (!ret) {
+            /* EOF case? */
+            fuse_log(FUSE_LOG_DEBUG, "%s: !ret len remaining=%zd\n", __func__,
+                     len);
+            break;
+        }
+        fuse_log(FUSE_LOG_DEBUG, "%s: preadv ret=%d len=%zd\n", __func__,
+                 ret, len);
+
+        len -= ret;
+        /* Short read. Retry reading remaining bytes */
+        if (len) {
+            fuse_log(FUSE_LOG_DEBUG, "%s: ret < len\n", __func__);
+            /* Skip over this much next time around */
+            iov_discard_front(&in_sg_ptr, &in_sg_cpy_count, ret);
+            buf->buf[0].pos += ret;
+        }
+    } while (len);
+
+    /* Need to fix out->len on EOF */
+    if (len) {
+        struct fuse_out_header *out_sg = in_sg[0].iov_base;
+
+        tosend_len -= len;
+        out_sg->len = tosend_len;
+    }
+
+    vq_send_element(qi, elem, tosend_len);
+    req->reply_sent = true;
+    return 0;
+}
+
+static __thread bool clone_fs_called;
+
+/* Process one FVRequest in a thread pool */
+static void fv_queue_worker(gpointer data, gpointer user_data)
+{
+    struct fv_QueueInfo *qi = user_data;
+    struct fuse_session *se = qi->virtio_dev->se;
+    FVRequest *req = data;
+    VuVirtqElement *elem = &req->elem;
+    struct fuse_buf fbuf = {};
+    bool allocated_bufv = false;
+    struct fuse_bufvec bufv;
+    struct fuse_bufvec *pbufv;
+    struct fuse_in_header inh;
+
+    assert(se->bufsize > sizeof(struct fuse_in_header));
+
+    if (!clone_fs_called) {
+        int ret;
+
+        /* unshare FS for xattr operation */
+        ret = unshare(CLONE_FS);
+        /* should not fail */
+        assert(ret == 0);
+
+        clone_fs_called = true;
+    }
+
+    /*
+     * An element contains one request and the space to send our response
+     * They're spread over multiple descriptors in a scatter/gather set
+     * and we can't trust the guest to keep them still; so copy in/out.
+     */
+    fbuf.mem = g_malloc(se->bufsize);
+
+    fuse_mutex_init(&req->ch.lock);
+    req->ch.fd = -1;
+    req->ch.qi = qi;
+
+    /* The 'out' part of the elem is from qemu */
+    unsigned int out_num = elem->out_num;
+    struct iovec *out_sg = elem->out_sg;
+    size_t out_len = iov_size(out_sg, out_num);
+    fuse_log(FUSE_LOG_DEBUG,
+             "%s: elem %d: with %d out desc of length %zd\n",
+             __func__, elem->index, out_num, out_len);
+
+    /*
+     * The elem should contain a 'fuse_in_header' (in to fuse)
+     * plus the data based on the len in the header.
+     */
+    if (out_len < sizeof(struct fuse_in_header)) {
+        fuse_log(FUSE_LOG_ERR, "%s: elem %d too short for in_header\n",
+                 __func__, elem->index);
+        assert(0); /* TODO */
+    }
+    if (out_len > se->bufsize) {
+        fuse_log(FUSE_LOG_ERR, "%s: elem %d too large for buffer\n", __func__,
+                 elem->index);
+        assert(0); /* TODO */
+    }
+    /* Copy just the fuse_in_header and look at it */
+    copy_from_iov(&fbuf, out_num, out_sg,
+                  sizeof(struct fuse_in_header));
+    memcpy(&inh, fbuf.mem, sizeof(struct fuse_in_header));
+
+    pbufv = NULL; /* Compiler thinks an unitialised path */
+    if (inh.opcode == FUSE_WRITE &&
+        out_len >= (sizeof(struct fuse_in_header) +
+                    sizeof(struct fuse_write_in))) {
+        /*
+         * For a write we don't actually need to copy the
+         * data, we can just do it straight out of guest memory
+         * but we must still copy the headers in case the guest
+         * was nasty and changed them while we were using them.
+         */
+        fuse_log(FUSE_LOG_DEBUG, "%s: Write special case\n", __func__);
+
+        fbuf.size = copy_from_iov(&fbuf, out_num, out_sg,
+                                  sizeof(struct fuse_in_header) +
+                                  sizeof(struct fuse_write_in));
+        /* That copy reread the in_header, make sure we use the original */
+        memcpy(fbuf.mem, &inh, sizeof(struct fuse_in_header));
+
+        /* Allocate the bufv, with space for the rest of the iov */
+        pbufv = g_try_malloc(sizeof(struct fuse_bufvec) +
+                             sizeof(struct fuse_buf) * out_num);
+        if (!pbufv) {
+            fuse_log(FUSE_LOG_ERR, "%s: pbufv malloc failed\n",
+                    __func__);
+            goto out;
+        }
+
+        allocated_bufv = true;
+        pbufv->count = 1;
+        pbufv->buf[0] = fbuf;
+
+        size_t iovindex, pbufvindex, iov_bytes_skip;
+        pbufvindex = 1; /* 2 headers, 1 fusebuf */
+
+        if (!skip_iov(out_sg, out_num,
+                      sizeof(struct fuse_in_header) +
+                      sizeof(struct fuse_write_in),
+                      &iovindex, &iov_bytes_skip)) {
+            fuse_log(FUSE_LOG_ERR, "%s: skip failed\n",
+                    __func__);
+            goto out;
+        }
+
+        for (; iovindex < out_num; iovindex++, pbufvindex++) {
+            pbufv->count++;
+            pbufv->buf[pbufvindex].pos = ~0; /* Dummy */
+            pbufv->buf[pbufvindex].flags = 0;
+            pbufv->buf[pbufvindex].mem = out_sg[iovindex].iov_base;
+            pbufv->buf[pbufvindex].size = out_sg[iovindex].iov_len;
+
+            if (iov_bytes_skip) {
+                pbufv->buf[pbufvindex].mem += iov_bytes_skip;
+                pbufv->buf[pbufvindex].size -= iov_bytes_skip;
+                iov_bytes_skip = 0;
+            }
+        }
+    } else {
+        /* Normal (non fast write) path */
+
+        copy_from_iov(&fbuf, out_num, out_sg, se->bufsize);
+        /* That copy reread the in_header, make sure we use the original */
+        memcpy(fbuf.mem, &inh, sizeof(struct fuse_in_header));
+        fbuf.size = out_len;
+
+        /* TODO! Endianness of header */
+
+        /* TODO: Add checks for fuse_session_exited */
+        bufv.buf[0] = fbuf;
+        bufv.count = 1;
+        pbufv = &bufv;
+    }
+    pbufv->idx = 0;
+    pbufv->off = 0;
+    fuse_session_process_buf_int(se, pbufv, &req->ch);
+
+out:
+    if (allocated_bufv) {
+        g_free(pbufv);
+    }
+
+    /* If the request has no reply, still recycle the virtqueue element */
+    if (!req->reply_sent) {
+        fuse_log(FUSE_LOG_DEBUG, "%s: elem %d no reply sent\n", __func__,
+                 elem->index);
+        vq_send_element(qi, elem, 0);
+    }
+
+    pthread_mutex_destroy(&req->ch.lock);
+    g_free(fbuf.mem);
+    free(req);
+}
+
+/* Thread function for individual queues, created when a queue is 'started' */
+static void *fv_queue_thread(void *opaque)
+{
+    struct fv_QueueInfo *qi = opaque;
+    struct VuDev *dev = &qi->virtio_dev->dev;
+    struct VuVirtq *q = vu_get_queue(dev, qi->qidx);
+    struct fuse_session *se = qi->virtio_dev->se;
+    GThreadPool *pool = NULL;
+    GList *req_list = NULL;
+
+    if (se->thread_pool_size) {
+        fuse_log(FUSE_LOG_DEBUG, "%s: Creating thread pool for Queue %d\n",
+                 __func__, qi->qidx);
+        pool = g_thread_pool_new(fv_queue_worker, qi, se->thread_pool_size,
+                                 FALSE, NULL);
+        if (!pool) {
+            fuse_log(FUSE_LOG_ERR, "%s: g_thread_pool_new failed\n", __func__);
+            return NULL;
+        }
+    }
+
+    fuse_log(FUSE_LOG_INFO, "%s: Start for queue %d kick_fd %d\n", __func__,
+             qi->qidx, qi->kick_fd);
+    while (1) {
+        struct pollfd pf[2];
+
+        pf[0].fd = qi->kick_fd;
+        pf[0].events = POLLIN;
+        pf[0].revents = 0;
+        pf[1].fd = qi->kill_fd;
+        pf[1].events = POLLIN;
+        pf[1].revents = 0;
+
+        fuse_log(FUSE_LOG_DEBUG, "%s: Waiting for Queue %d event\n", __func__,
+                 qi->qidx);
+        int poll_res = ppoll(pf, 2, NULL, NULL);
+
+        if (poll_res == -1) {
+            if (errno == EINTR) {
+                fuse_log(FUSE_LOG_INFO, "%s: ppoll interrupted, going around\n",
+                         __func__);
+                continue;
+            }
+            fuse_log(FUSE_LOG_ERR, "fv_queue_thread ppoll: %m\n");
+            break;
+        }
+        assert(poll_res >= 1);
+        if (pf[0].revents & (POLLERR | POLLHUP | POLLNVAL)) {
+            fuse_log(FUSE_LOG_ERR, "%s: Unexpected poll revents %x Queue %d\n",
+                     __func__, pf[0].revents, qi->qidx);
+            break;
+        }
+        if (pf[1].revents & (POLLERR | POLLHUP | POLLNVAL)) {
+            fuse_log(FUSE_LOG_ERR,
+                     "%s: Unexpected poll revents %x Queue %d killfd\n",
+                     __func__, pf[1].revents, qi->qidx);
+            break;
+        }
+        if (pf[1].revents) {
+            fuse_log(FUSE_LOG_INFO, "%s: kill event on queue %d - quitting\n",
+                     __func__, qi->qidx);
+            break;
+        }
+        assert(pf[0].revents & POLLIN);
+        fuse_log(FUSE_LOG_DEBUG, "%s: Got queue event on Queue %d\n", __func__,
+                 qi->qidx);
+
+        eventfd_t evalue;
+        if (eventfd_read(qi->kick_fd, &evalue)) {
+            fuse_log(FUSE_LOG_ERR, "Eventfd_read for queue: %m\n");
+            break;
+        }
+        /* Mutual exclusion with virtio_loop() */
+        vu_dispatch_rdlock(qi->virtio_dev);
+        pthread_mutex_lock(&qi->vq_lock);
+        /* out is from guest, in is too guest */
+        unsigned int in_bytes, out_bytes;
+        vu_queue_get_avail_bytes(dev, q, &in_bytes, &out_bytes, ~0, ~0);
+
+        fuse_log(FUSE_LOG_DEBUG,
+                 "%s: Queue %d gave evalue: %zx available: in: %u out: %u\n",
+                 __func__, qi->qidx, (size_t)evalue, in_bytes, out_bytes);
+
+        while (1) {
+            FVRequest *req = vu_queue_pop(dev, q, sizeof(FVRequest));
+            if (!req) {
+                break;
+            }
+
+            req->reply_sent = false;
+
+            if (!se->thread_pool_size) {
+                req_list = g_list_prepend(req_list, req);
+            } else {
+                g_thread_pool_push(pool, req, NULL);
+            }
+        }
+
+        pthread_mutex_unlock(&qi->vq_lock);
+        vu_dispatch_unlock(qi->virtio_dev);
+
+        /* Process all the requests. */
+        if (!se->thread_pool_size && req_list != NULL) {
+            req_list = g_list_reverse(req_list);
+            g_list_foreach(req_list, fv_queue_worker, qi);
+            g_list_free(req_list);
+            req_list = NULL;
+        }
+    }
+
+    if (pool) {
+        g_thread_pool_free(pool, FALSE, TRUE);
+    }
+
+    return NULL;
+}
+
+static void fv_queue_cleanup_thread(struct fv_VuDev *vud, int qidx)
+{
+    int ret;
+    struct fv_QueueInfo *ourqi;
+
+    assert(qidx < vud->nqueues);
+    ourqi = vud->qi[qidx];
+
+    /* Kill the thread */
+    if (eventfd_write(ourqi->kill_fd, 1)) {
+        fuse_log(FUSE_LOG_ERR, "Eventfd_write for queue %d: %s\n",
+                 qidx, strerror(errno));
+    }
+    ret = pthread_join(ourqi->thread, NULL);
+    if (ret) {
+        fuse_log(FUSE_LOG_ERR, "%s: Failed to join thread idx %d err %d\n",
+                 __func__, qidx, ret);
+    }
+    pthread_mutex_destroy(&ourqi->vq_lock);
+    close(ourqi->kill_fd);
+    ourqi->kick_fd = -1;
+    g_free(vud->qi[qidx]);
+    vud->qi[qidx] = NULL;
+}
+
+static void stop_all_queues(struct fv_VuDev *vud)
+{
+    for (int i = 0; i < vud->nqueues; i++) {
+        if (!vud->qi[i]) {
+            continue;
+        }
+
+        fuse_log(FUSE_LOG_INFO, "%s: Stopping queue %d thread\n", __func__, i);
+        fv_queue_cleanup_thread(vud, i);
+    }
+}
+
+/* Callback from libvhost-user on start or stop of a queue */
+static void fv_queue_set_started(VuDev *dev, int qidx, bool started)
+{
+    struct fv_VuDev *vud = container_of(dev, struct fv_VuDev, dev);
+    struct fv_QueueInfo *ourqi;
+
+    fuse_log(FUSE_LOG_INFO, "%s: qidx=%d started=%d\n", __func__, qidx,
+             started);
+    assert(qidx >= 0);
+
+    /*
+     * Ignore additional request queues for now.  passthrough_ll.c must be
+     * audited for thread-safety issues first.  It was written with a
+     * well-behaved client in mind and may not protect against all types of
+     * races yet.
+     */
+    if (qidx > 1) {
+        fuse_log(FUSE_LOG_ERR,
+                 "%s: multiple request queues not yet implemented, please only "
+                 "configure 1 request queue\n",
+                 __func__);
+        exit(EXIT_FAILURE);
+    }
+
+    if (started) {
+        /* Fire up a thread to watch this queue */
+        if (qidx >= vud->nqueues) {
+            vud->qi = g_realloc_n(vud->qi, qidx + 1, sizeof(vud->qi[0]));
+            memset(vud->qi + vud->nqueues, 0,
+                   sizeof(vud->qi[0]) * (1 + (qidx - vud->nqueues)));
+            vud->nqueues = qidx + 1;
+        }
+        if (!vud->qi[qidx]) {
+            vud->qi[qidx] = g_new0(struct fv_QueueInfo, 1);
+            vud->qi[qidx]->virtio_dev = vud;
+            vud->qi[qidx]->qidx = qidx;
+        } else {
+            /* Shouldn't have been started */
+            assert(vud->qi[qidx]->kick_fd == -1);
+        }
+        ourqi = vud->qi[qidx];
+        ourqi->kick_fd = dev->vq[qidx].kick_fd;
+
+        ourqi->kill_fd = eventfd(0, EFD_CLOEXEC | EFD_SEMAPHORE);
+        assert(ourqi->kill_fd != -1);
+        pthread_mutex_init(&ourqi->vq_lock, NULL);
+
+        if (pthread_create(&ourqi->thread, NULL, fv_queue_thread, ourqi)) {
+            fuse_log(FUSE_LOG_ERR, "%s: Failed to create thread for queue %d\n",
+                     __func__, qidx);
+            assert(0);
+        }
+    } else {
+        /*
+         * Temporarily drop write-lock taken in virtio_loop() so that
+         * the queue thread doesn't block in virtio_send_msg().
+         */
+        vu_dispatch_unlock(vud);
+        fv_queue_cleanup_thread(vud, qidx);
+        vu_dispatch_wrlock(vud);
+    }
+}
+
+static bool fv_queue_order(VuDev *dev, int qidx)
+{
+    return false;
+}
+
+static const VuDevIface fv_iface = {
+    .get_features = fv_get_features,
+    .set_features = fv_set_features,
+
+    /* Don't need process message, we've not got any at vhost-user level */
+    .queue_set_started = fv_queue_set_started,
+
+    .queue_is_processed_in_order = fv_queue_order,
+};
+
+/*
+ * Main loop; this mostly deals with events on the vhost-user
+ * socket itself, and not actual fuse data.
+ */
+int virtio_loop(struct fuse_session *se)
+{
+    fuse_log(FUSE_LOG_INFO, "%s: Entry\n", __func__);
+
+    while (!fuse_session_exited(se)) {
+        struct pollfd pf[1];
+        bool ok;
+        pf[0].fd = se->vu_socketfd;
+        pf[0].events = POLLIN;
+        pf[0].revents = 0;
+
+        fuse_log(FUSE_LOG_DEBUG, "%s: Waiting for VU event\n", __func__);
+        int poll_res = ppoll(pf, 1, NULL, NULL);
+
+        if (poll_res == -1) {
+            if (errno == EINTR) {
+                fuse_log(FUSE_LOG_INFO, "%s: ppoll interrupted, going around\n",
+                         __func__);
+                continue;
+            }
+            fuse_log(FUSE_LOG_ERR, "virtio_loop ppoll: %m\n");
+            break;
+        }
+        assert(poll_res == 1);
+        if (pf[0].revents & (POLLERR | POLLHUP | POLLNVAL)) {
+            fuse_log(FUSE_LOG_ERR, "%s: Unexpected poll revents %x\n", __func__,
+                     pf[0].revents);
+            break;
+        }
+        assert(pf[0].revents & POLLIN);
+        fuse_log(FUSE_LOG_DEBUG, "%s: Got VU event\n", __func__);
+        /* Mutual exclusion with fv_queue_thread() */
+        vu_dispatch_wrlock(se->virtio_dev);
+
+        ok = vu_dispatch(&se->virtio_dev->dev);
+
+        vu_dispatch_unlock(se->virtio_dev);
+
+        if (!ok) {
+            fuse_log(FUSE_LOG_ERR, "%s: vu_dispatch failed\n", __func__);
+            break;
+        }
+    }
+
+    /*
+     * Make sure all fv_queue_thread()s quit on exit, as we're about to
+     * free virtio dev and fuse session, no one should access them anymore.
+     */
+    stop_all_queues(se->virtio_dev);
+    fuse_log(FUSE_LOG_INFO, "%s: Exit\n", __func__);
+
+    return 0;
+}
+
+static void strreplace(char *s, char old, char new)
+{
+    for (; *s; ++s) {
+        if (*s == old) {
+            *s = new;
+        }
+    }
+}
+
+static bool fv_socket_lock(struct fuse_session *se)
+{
+    g_autofree gchar *sk_name = NULL;
+    g_autofree gchar *pidfile = NULL;
+    g_autofree gchar *dir = NULL;
+    Error *local_err = NULL;
+
+    dir = qemu_get_local_state_pathname("run/virtiofsd");
+
+    if (g_mkdir_with_parents(dir, S_IRWXU) < 0) {
+        fuse_log(FUSE_LOG_ERR, "%s: Failed to create directory %s: %s\n",
+                 __func__, dir, strerror(errno));
+        return false;
+    }
+
+    sk_name = g_strdup(se->vu_socket_path);
+    strreplace(sk_name, '/', '.');
+    pidfile = g_strdup_printf("%s/%s.pid", dir, sk_name);
+
+    if (!qemu_write_pidfile(pidfile, &local_err)) {
+        error_report_err(local_err);
+        return false;
+    }
+
+    return true;
+}
+
+static int fv_create_listen_socket(struct fuse_session *se)
+{
+    struct sockaddr_un un;
+    mode_t old_umask;
+
+    /* Nothing to do if fd is already initialized */
+    if (se->vu_listen_fd >= 0) {
+        return 0;
+    }
+
+    if (strlen(se->vu_socket_path) >= sizeof(un.sun_path)) {
+        fuse_log(FUSE_LOG_ERR, "Socket path too long\n");
+        return -1;
+    }
+
+    if (!strlen(se->vu_socket_path)) {
+        fuse_log(FUSE_LOG_ERR, "Socket path is empty\n");
+        return -1;
+    }
+
+    /* Check the vu_socket_path is already used */
+    if (!fv_socket_lock(se)) {
+        return -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 appropriately and restore it later.
+     */
+    if (se->vu_socket_group) {
+        old_umask = umask(S_IROTH | S_IWOTH | S_IXOTH);
+    } else {
+        old_umask = umask(S_IRGRP | S_IWGRP | S_IXGRP |
+                          S_IROTH | S_IWOTH | S_IXOTH);
+    }
+    if (bind(listen_sock, (struct sockaddr *)&un, addr_len) == -1) {
+        fuse_log(FUSE_LOG_ERR, "vhost socket bind: %m\n");
+        close(listen_sock);
+        umask(old_umask);
+        return -1;
+    }
+    if (se->vu_socket_group) {
+        struct group *g = getgrnam(se->vu_socket_group);
+        if (g) {
+            if (chown(se->vu_socket_path, -1, g->gr_gid) == -1) {
+                fuse_log(FUSE_LOG_WARNING,
+                         "vhost socket failed to set group to %s (%d): %m\n",
+                         se->vu_socket_group, g->gr_gid);
+            }
+        } else {
+            fuse_log(FUSE_LOG_ERR,
+                     "vhost socket: unable to find group '%s'\n",
+                     se->vu_socket_group);
+            close(listen_sock);
+            umask(old_umask);
+            return -1;
+        }
+    }
+    umask(old_umask);
+
+    if (listen(listen_sock, 1) == -1) {
+        fuse_log(FUSE_LOG_ERR, "vhost socket listen: %m\n");
+        close(listen_sock);
+        return -1;
+    }
+
+    se->vu_listen_fd = listen_sock;
+    return 0;
+}
+
+int virtio_session_mount(struct fuse_session *se)
+{
+    int ret;
+
+    /*
+     * Test that unshare(CLONE_FS) works. fv_queue_worker() will need it. It's
+     * an unprivileged system call but some Docker/Moby versions are known to
+     * reject it via seccomp when CAP_SYS_ADMIN is not given.
+     *
+     * Note that the program is single-threaded here so this syscall has no
+     * visible effect and is safe to make.
+     */
+    ret = unshare(CLONE_FS);
+    if (ret == -1 && errno == EPERM) {
+        fuse_log(FUSE_LOG_ERR, "unshare(CLONE_FS) failed with EPERM. If "
+                "running in a container please check that the container "
+                "runtime seccomp policy allows unshare.\n");
+        return -1;
+    }
+
+    ret = fv_create_listen_socket(se);
+    if (ret < 0) {
+        return ret;
+    }
+
+    se->fd = -1;
+
+    fuse_log(FUSE_LOG_INFO, "%s: Waiting for vhost-user socket connection...\n",
+             __func__);
+    int data_sock = accept(se->vu_listen_fd, NULL, NULL);
+    if (data_sock == -1) {
+        fuse_log(FUSE_LOG_ERR, "vhost socket accept: %m\n");
+        close(se->vu_listen_fd);
+        return -1;
+    }
+    close(se->vu_listen_fd);
+    se->vu_listen_fd = -1;
+    fuse_log(FUSE_LOG_INFO, "%s: Received vhost-user socket connection\n",
+             __func__);
+
+    /* TODO: Some cleanup/deallocation! */
+    se->virtio_dev = g_new0(struct fv_VuDev, 1);
+
+    se->vu_socketfd = data_sock;
+    se->virtio_dev->se = se;
+    pthread_rwlock_init(&se->virtio_dev->vu_dispatch_rwlock, NULL);
+    if (!vu_init(&se->virtio_dev->dev, 2, se->vu_socketfd, fv_panic, NULL,
+                 fv_set_watch, fv_remove_watch, &fv_iface)) {
+        fuse_log(FUSE_LOG_ERR, "%s: vu_init failed\n", __func__);
+        return -1;
+    }
+
+    return 0;
+}
+
+void virtio_session_close(struct fuse_session *se)
+{
+    close(se->vu_socketfd);
+
+    if (!se->virtio_dev) {
+        return;
+    }
+
+    g_free(se->virtio_dev->qi);
+    pthread_rwlock_destroy(&se->virtio_dev->vu_dispatch_rwlock);
+    g_free(se->virtio_dev);
+    se->virtio_dev = NULL;
+}