From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>

Date: Mon, 27 Jan 2020 19:01:06 +0000

Subject: [PATCH] virtiofsd: Fast path for virtio read

Readv the data straight into the guests buffer.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

With fix by:

Signed-off-by: Eryu Guan <eguan@linux.alibaba.com>

Reviewed-by: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

(cherry picked from commit eb49d187ef5134483a34c970bbfece28aaa686a7)

---

 tools/virtiofsd/fuse_lowlevel.c |   5 +

 tools/virtiofsd/fuse_virtio.c   | 162 ++++++++++++++++++++++++++++++++

 tools/virtiofsd/fuse_virtio.h   |   4 +

 3 files changed, 171 insertions(+)

diff --git a/tools/virtiofsd/fuse_lowlevel.c b/tools/virtiofsd/fuse_lowlevel.c

index 380d93bd01..4f4684d942 100644

--- a/tools/virtiofsd/fuse_lowlevel.c

+++ b/tools/virtiofsd/fuse_lowlevel.c

@@ -475,6 +475,11 @@ static int fuse_send_data_iov_fallback(struct fuse_session *se,

         return fuse_send_msg(se, ch, iov, iov_count);

     }

+    if (fuse_lowlevel_is_virtio(se) && buf->count == 1 &&

+        buf->buf[0].flags == (FUSE_BUF_IS_FD | FUSE_BUF_FD_SEEK)) {

+        return virtio_send_data_iov(se, ch, iov, iov_count, buf, len);

+    }

+

     abort(); /* Will have taken vhost path */

     return 0;

 }

diff --git a/tools/virtiofsd/fuse_virtio.c b/tools/virtiofsd/fuse_virtio.c

index f1adeb6345..7e2711b504 100644

--- a/tools/virtiofsd/fuse_virtio.c

+++ b/tools/virtiofsd/fuse_virtio.c

@@ -230,6 +230,168 @@ 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)

+{

+    int ret = 0;

+    VuVirtqElement *elem;

+    VuVirtq *q;

+

+    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);

+

+    /* For virtio we always have ch */

+    assert(ch);

+    assert(!ch->qi->reply_sent);

+    elem = ch->qi->qe;

+    q = &ch->qi->virtio_dev->dev.vq[ch->qi->qidx];

+

+    /* 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;

+    }

+

+    /* 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

+     */

+    struct iovec *in_sg_cpy = calloc(sizeof(struct iovec), in_num);

+    assert(in_sg_cpy);

+    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;

+    int in_sg_cpy_count = in_num;

+

+    /* skip over parts of in_sg that contained the header iov */

+    size_t skip_size = iov_len;

+

+    size_t in_sg_left = 0;

+    do {

+        while (skip_size != 0 && in_sg_cpy_count) {

+            if (skip_size >= in_sg_ptr[0].iov_len) {

+                skip_size -= in_sg_ptr[0].iov_len;

+                in_sg_ptr++;

+                in_sg_cpy_count--;

+            } else {

+                in_sg_ptr[0].iov_len -= skip_size;

+                in_sg_ptr[0].iov_base += skip_size;

+                break;

+            }

+        }

+

+        int i;

+        for (i = 0, in_sg_left = 0; i < in_sg_cpy_count; i++) {

+            in_sg_left += in_sg_ptr[i].iov_len;

+        }

+        fuse_log(FUSE_LOG_DEBUG,

+                 "%s: after skip skip_size=%zd in_sg_cpy_count=%d "

+                 "in_sg_left=%zd\n",

+                 __func__, skip_size, in_sg_cpy_count, in_sg_left);

+        ret = preadv(buf->buf[0].fd, in_sg_ptr, in_sg_cpy_count,

+                     buf->buf[0].pos);

+

+        if (ret == -1) {

+            ret = errno;

+            fuse_log(FUSE_LOG_DEBUG, "%s: preadv failed (%m) len=%zd\n",

+                     __func__, len);

+            free(in_sg_cpy);

+            goto err;

+        }

+        fuse_log(FUSE_LOG_DEBUG, "%s: preadv ret=%d len=%zd\n", __func__,

+                 ret, len);

+        if (ret < len && ret) {

+            fuse_log(FUSE_LOG_DEBUG, "%s: ret < len\n", __func__);

+            /* Skip over this much next time around */

+            skip_size = ret;

+            buf->buf[0].pos += ret;

+            len -= ret;

+

+            /* Lets do another read */

+            continue;

+        }

+        if (!ret) {

+            /* EOF case? */

+            fuse_log(FUSE_LOG_DEBUG, "%s: !ret in_sg_left=%zd\n", __func__,

+                     in_sg_left);

+            break;

+        }

+        if (ret != len) {

+            fuse_log(FUSE_LOG_DEBUG, "%s: ret!=len\n", __func__);

+            ret = EIO;

+            free(in_sg_cpy);

+            goto err;

+        }

+        in_sg_left -= ret;

+        len -= ret;

+    } while (in_sg_left);

+    free(in_sg_cpy);

+

+    /* 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;

+    }

+

+    ret = 0;

+

+    vu_queue_push(&se->virtio_dev->dev, q, elem, tosend_len);

+    vu_queue_notify(&se->virtio_dev->dev, q);

+

+err:

+    if (ret == 0) {

+        ch->qi->reply_sent = true;

+    }

+

+    return ret;

+}

+

 /* Thread function for individual queues, created when a queue is 'started' */

 static void *fv_queue_thread(void *opaque)

 {

diff --git a/tools/virtiofsd/fuse_virtio.h b/tools/virtiofsd/fuse_virtio.h

index 135a14875a..cc676b9193 100644

--- a/tools/virtiofsd/fuse_virtio.h

+++ b/tools/virtiofsd/fuse_virtio.h

@@ -26,4 +26,8 @@ int virtio_loop(struct fuse_session *se);

 int virtio_send_msg(struct fuse_session *se, struct fuse_chan *ch,

                     struct iovec *iov, int count);

+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);

+

 #endif