qga: set file descriptor in qmp_guest_file_open non-blocking on Win32

Set fd non-blocking to avoid common use cases (like reading from a
named pipe) from hanging the agent. This was missed in the original
code.

The patch introduces qemu_set_handle_nonoblocking, the local analog
of qemu_set_nonblock for HANDLES.
The usage of handles in qemu_set_non/block is impossible, because for
win32 there is a difference between file discriptors and file handles,
and all file ops are made via Win32 api.

Signed-off-by: Olga Krishtal <okrishtal@parallels.com>
Signed-off-by: Denis V. Lunev <den@openvz.org>
CC: Michael Roth <mdroth@linux.vnet.ibm.com>
CC: Stefan Weil <sw@weilnetz.de>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

qga/commands-win32.c

diff --git a/qga/commands-win32.c b/qga/commands-win32.c
index 97f19d5..a5306e7 100644
--- a/qga/commands-win32.c
+++ b/qga/commands-win32.c
@@ -128,6 +128,28 @@
     return NULL;
 }
 
+static void handle_set_nonblocking(HANDLE fh)
+{
+    DWORD file_type, pipe_state;
+    file_type = GetFileType(fh);
+    if (file_type != FILE_TYPE_PIPE) {
+        return;
+    }
+    /* If file_type == FILE_TYPE_PIPE, according to MSDN
+     * the specified file is socket or named pipe */
+    if (!GetNamedPipeHandleState(fh, &pipe_state, NULL,
+                                 NULL, NULL, NULL, 0)) {
+        return;
+    }
+    /* The fd is named pipe fd */
+    if (pipe_state & PIPE_NOWAIT) {
+        return;
+    }
+
+    pipe_state |= PIPE_NOWAIT;
+    SetNamedPipeHandleState(fh, &pipe_state, NULL, NULL);
+}
+
 int64_t qmp_guest_file_open(const char *path, bool has_mode,
                             const char *mode, Error **errp)
 {
@@ -158,6 +180,11 @@
         return -1;
     }
 
+    /* set fd non-blocking to avoid common use cases (like reading from a
+     * named pipe) from hanging the agent
+     */
+    handle_set_nonblocking(fh);
+
     fd = guest_file_handle_add(fh, errp);
     if (fd < 0) {
         CloseHandle(fh);