From: Wen Congyang <wency@cn.fujitsu.com>
Date: Mon, 16 Mar 2015 13:29:50 +0000 (+0000)
Subject: tools/libxl: Update datacopier to support sending data only
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tools/libxl: Update datacopier to support sending data only

Currently, starting a datacopier requires a valid read and write fd, but this
is a problem when purely sending data from a local buffer to a writable fd.

The prefixdata mechanism already exists and works for inserting data from a
local buffer ahead of reading from the read fd.

Make the lack of a read fd non-fatal.  A datacopier with no read fd, but some
prefixdata will write the prefixdata to the write fd and complete successfully.

Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>
[Rewrite commit message]
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
CC: Ian Campbell <Ian.Campbell@citrix.com>
CC: Ian Jackson <Ian.Jackson@eu.citrix.com>
CC: Wei Liu <wei.liu2@citrix.com>
---

diff --git a/tools/libxl/libxl_aoutils.c b/tools/libxl/libxl_aoutils.c
index b10d2e1583..3e0c0aefa7 100644
--- a/tools/libxl/libxl_aoutils.c
+++ b/tools/libxl/libxl_aoutils.c
@@ -309,9 +309,11 @@ int libxl__datacopier_start(libxl__datacopier_state *dc)
 
     libxl__datacopier_init(dc);
 
-    rc = libxl__ev_fd_register(gc, &dc->toread, datacopier_readable,
-                               dc->readfd, POLLIN);
-    if (rc) goto out;
+    if (dc->readfd >= 0) {
+        rc = libxl__ev_fd_register(gc, &dc->toread, datacopier_readable,
+                                   dc->readfd, POLLIN);
+        if (rc) goto out;
+    }
 
     rc = libxl__ev_fd_register(gc, &dc->towrite, datacopier_writable,
                                dc->writefd, POLLOUT);