util: Make it safe to call virFileWrapperFdClose() multiple times

We'll want to use this function in the cleanup path soon,
and in order to be able to do that we need to make sure we
can call it multiple times on the same virFileWrapperFd
without side effects.
Signed-off-by: NAndrea Bolognani <abologna@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>

src/util/virfile.c

@@ -175,6 +175,7 @@ virFileDirectFdFlag(void)
 /* Opaque type for managing a wrapper around a fd.  For now,
  * read-write is not supported, just a single direction.  */
 struct _virFileWrapperFd {
+    bool closed; /* Whether virFileWrapperFdClose() has been already called */
     virCommandPtr cmd; /* Child iohelper process to do the I/O.  */
     char *err_msg; /* stderr of @cmd */
 };
@@ -323,16 +324,21 @@ virFileWrapperFdNew(int *fd ATTRIBUTE_UNUSED,
  * callers can conditionally create a virFileWrapperFd wrapper but
  * unconditionally call the cleanup code.  To avoid deadlock, only
  * call this after closing the fd resulting from virFileWrapperFdNew().
+ *
+ * This function can be safely called multiple times on the same @wfd.
  */
 int
 virFileWrapperFdClose(virFileWrapperFdPtr wfd)
 {
     int ret;
 
-    if (!wfd)
+    if (!wfd || wfd->closed)
         return 0;
 
     ret = virCommandWait(wfd->cmd, NULL);
+
+    wfd->closed = true;
+
     return ret;
 }