From: piaojun <piaojun@huawei.com>
Date: Mon, 27 Jan 2020 19:02:18 +0000
Subject: [PATCH] virtiofsd: use fuse_buf_writev to replace fuse_buf_write for
 better performance
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fuse_buf_writev() only handles the normal write in which src is buffer
and dest is fd. Specially if src buffer represents guest physical
address that can't be mapped by the daemon process, IO must be bounced
back to the VMM to do it by fuse_buf_copy().

Signed-off-by: Jun Piao <piaojun@huawei.com>
Suggested-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Suggested-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
(cherry picked from commit c465bba2c90a810f6e71e4f2646b1b4ee4b478de)
---
 tools/virtiofsd/buffer.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/tools/virtiofsd/buffer.c b/tools/virtiofsd/buffer.c
index 37befebac2..27c1377f22 100644
--- a/tools/virtiofsd/buffer.c
+++ b/tools/virtiofsd/buffer.c
@@ -34,7 +34,6 @@ size_t fuse_buf_size(const struct fuse_bufvec *bufv)
     return size;
 }
 
-__attribute__((unused))
 static ssize_t fuse_buf_writev(struct fuse_buf *out_buf,
                                struct fuse_bufvec *in_buf)
 {
@@ -262,12 +261,29 @@ static int fuse_bufvec_advance(struct fuse_bufvec *bufv, size_t len)
 
 ssize_t fuse_buf_copy(struct fuse_bufvec *dstv, struct fuse_bufvec *srcv)
 {
-    size_t copied = 0;
+    size_t copied = 0, i;
 
     if (dstv == srcv) {
         return fuse_buf_size(dstv);
     }
 
+    /*
+     * use writev to improve bandwidth when all the
+     * src buffers already mapped by the daemon
+     * process
+     */
+    for (i = 0; i < srcv->count; i++) {
+        if (srcv->buf[i].flags & FUSE_BUF_IS_FD) {
+            break;
+        }
+    }
+    if ((i == srcv->count) && (dstv->count == 1) &&
+        (dstv->idx == 0) &&
+        (dstv->buf[0].flags & FUSE_BUF_IS_FD)) {
+        dstv->buf[0].pos += dstv->off;
+        return fuse_buf_writev(&dstv->buf[0], srcv);
+    }
+
     for (;;) {
         const struct fuse_buf *src = fuse_bufvec_current(srcv);
         const struct fuse_buf *dst = fuse_bufvec_current(dstv);