migration: introduce set_blocking function in QEMUFileOps

Remove the assumption that every QEMUFile implementation has
a file descriptor available by introducing a new function
in QEMUFileOps to change the blocking state of a QEMUFile.

If not set, it will fallback to the original code using
the get_fd method.

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Message-Id: <1461751518-12128-7-git-send-email-berrange@redhat.com>
Signed-off-by: Amit Shah <amit.shah@redhat.com>

include/migration/qemu-file.h

@@ -54,6 +54,10 @@ typedef int (QEMUFileCloseFunc)(void *opaque);
  */
 typedef int (QEMUFileGetFD)(void *opaque);
 
+/* Called to change the blocking mode of the file
+ */
+typedef int (QEMUFileSetBlocking)(void *opaque, bool enabled);
+
 /*
  * This function writes an iovec to file. The handler must write all
  * of the data or return a negative errno value.
@@ -107,6 +111,7 @@ typedef struct QEMUFileOps {
     QEMUFileGetBufferFunc *get_buffer;
     QEMUFileCloseFunc *close;
     QEMUFileGetFD *get_fd;
+    QEMUFileSetBlocking *set_blocking;
     QEMUFileWritevBufferFunc *writev_buffer;
     QEMURetPathFunc *get_return_path;
     QEMUFileShutdownFunc *shut_down;

migration/migration.c

@@ -422,11 +422,9 @@ static void process_incoming_migration_co(void *opaque)
 void process_incoming_migration(QEMUFile *f)
 {
     Coroutine *co = qemu_coroutine_create(process_incoming_migration_co);
-    int fd = qemu_get_fd(f);
 
-    assert(fd != -1);
     migrate_decompress_threads_create();
-    qemu_set_nonblock(fd);
+    qemu_file_set_blocking(f, false);
     qemu_coroutine_enter(co, f);
 }
 

migration/qemu-file.c

@@ -684,9 +684,13 @@ size_t qemu_get_counted_string(QEMUFile *f, char buf[256])
  */
 void qemu_file_set_blocking(QEMUFile *f, bool block)
 {
-    if (block) {
-        qemu_set_block(qemu_get_fd(f));
+    if (f->ops->set_blocking) {
+        f->ops->set_blocking(f->opaque, block);
     } else {
-        qemu_set_nonblock(qemu_get_fd(f));
+        if (block) {
+            qemu_set_block(qemu_get_fd(f));
+        } else {
+            qemu_set_nonblock(qemu_get_fd(f));
+        }
     }
 }