[Virtio-fs] [PATCH v2 2/2][RFC] use fuse_buf_writev to replace fuse_buf_write for better performance

[piaojun]

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 at huawei.com>
Suggested-by: Dr. David Alan Gilbert <dgilbert at redhat.com>
---
 contrib/virtiofsd/passthrough_ll.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/contrib/virtiofsd/passthrough_ll.c b/contrib/virtiofsd/passthrough_ll.c
index cc9c175..c1bbc53 100644
--- a/contrib/virtiofsd/passthrough_ll.c
+++ b/contrib/virtiofsd/passthrough_ll.c
@@ -2023,7 +2023,10 @@ static void lo_write_buf(fuse_req_t req, fuse_ino_t ino,
 		fuse_debug("lo_write_buf(ino=%" PRIu64 ", size=%zd, off=%lu)\n",
 			   ino, out_buf.buf[0].size, (unsigned long) off);

-	res = fuse_buf_copy(req, &out_buf, in_buf, 0);
+	if (!(in_buf->buf[0].flags & FUSE_BUF_PHYS_ADDR))
+		res = fuse_buf_writev(req, &out_buf, in_buf, out_buf.buf[0].flags);
+	else
+		res = fuse_buf_copy(req, &out_buf, in_buf, 0);
 	if(res < 0) {
 		fuse_reply_err(req, -res);
 	} else {
--