Add wrapper for setting blocking status on a QEMUFile

Add a wrapper to change the blocking status on a QEMUFile
rather than having to use qemu_set_block(qemu_get_fd(f));
it seems best to avoid exposing the fd since not all QEMUFile's
really have one.  With this wrapper we could move the implementation
down to be different on different transports.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Amit Shah <amit.shah@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

include/migration/qemu-file.h

diff --git a/include/migration/qemu-file.h b/include/migration/qemu-file.h
index 86bb972..66e741f 100644
--- a/include/migration/qemu-file.h
+++ b/include/migration/qemu-file.h
@@ -197,6 +197,7 @@
 void qemu_file_set_error(QEMUFile *f, int ret);
 int qemu_file_shutdown(QEMUFile *f);
 void qemu_fflush(QEMUFile *f);
+void qemu_file_set_blocking(QEMUFile *f, bool block);
 
 static inline void qemu_put_be64s(QEMUFile *f, const uint64_t *pv)
 {

migration/qemu-file.c

diff --git a/migration/qemu-file.c b/migration/qemu-file.c
index e41a677..9ec2267 100644
--- a/migration/qemu-file.c
+++ b/migration/qemu-file.c
@@ -648,3 +648,18 @@
 
     return res == len ? res : 0;
 }
+
+/*
+ * Set the blocking state of the QEMUFile.
+ * Note: On some transports the OS only keeps a single blocking state for
+ *       both directions, and thus changing the blocking on the main
+ *       QEMUFile can also affect the return path.
+ */
+void qemu_file_set_blocking(QEMUFile *f, bool block)
+{
+    if (block) {
+        qemu_set_block(qemu_get_fd(f));
+    } else {
+        qemu_set_nonblock(qemu_get_fd(f));
+    }
+}