ram compress: Assert that the file buffer matches the result

Before this series, "nothing to send" was handled by the file buffer
being empty. Now it is tracked via param->result.

Assert that the file buffer state matches the result.

Signed-off-by: Lukas Straub <lukasstraub2@web.de>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

migration/qemu-file.c

@@ -870,6 +870,17 @@ int qemu_put_qemu_file(QEMUFile *f_des, QEMUFile *f_src)
     return len;
 }
 
+/*
+ * Check if the writable buffer is empty
+ */
+
+bool qemu_file_buffer_empty(QEMUFile *file)
+{
+    assert(qemu_file_is_writable(file));
+
+    return !file->iovcnt;
+}
+
 /*
  * Get a string whose length is determined by a single preceding byte
  * A preallocated 256 byte buffer must be passed in.

migration/qemu-file.h

@@ -113,6 +113,7 @@ size_t coroutine_mixed_fn qemu_get_buffer_in_place(QEMUFile *f, uint8_t **buf, s
 ssize_t qemu_put_compression_data(QEMUFile *f, z_stream *stream,
                                   const uint8_t *p, size_t size);
 int qemu_put_qemu_file(QEMUFile *f_des, QEMUFile *f_src);
+bool qemu_file_buffer_empty(QEMUFile *file);
 
 /*
  * Note that you can only peek continuous bytes from where the current pointer

migration/ram-compress.c

@@ -194,6 +194,8 @@ static CompressResult do_compress_ram_page(QEMUFile *f, z_stream *stream,
     uint8_t *p = block->host + offset;
     int ret;
 
+    assert(qemu_file_buffer_empty(f));
+
     if (buffer_is_zero(p, TARGET_PAGE_SIZE)) {
         return RES_ZEROPAGE;
     }
@@ -208,6 +210,7 @@ static CompressResult do_compress_ram_page(QEMUFile *f, z_stream *stream,
     if (ret < 0) {
         qemu_file_set_error(migrate_get_current()->to_dst_file, ret);
         error_report("compressed data failed!");
+        qemu_fflush(f);
         return RES_NONE;
     }
     return RES_COMPRESS;
@@ -239,6 +242,7 @@ void flush_compressed_data(int (send_queued_data(CompressParam *)))
         if (!comp_param[idx].quit) {
             CompressParam *param = &comp_param[idx];
             send_queued_data(param);
+            assert(qemu_file_buffer_empty(param->file));
             compress_reset_result(param);
         }
         qemu_mutex_unlock(&comp_param[idx].mutex);
@@ -268,6 +272,7 @@ int compress_page_with_multi_thread(RAMBlock *block, ram_addr_t offset,
             qemu_mutex_lock(&param->mutex);
             param->done = false;
             send_queued_data(param);
+            assert(qemu_file_buffer_empty(param->file));
             compress_reset_result(param);
             set_compress_params(param, block, offset);
 

migration/ram.c

@@ -1321,11 +1321,13 @@ static int send_queued_data(CompressParam *param)
     assert(block == pss->last_sent_block);
 
     if (param->result == RES_ZEROPAGE) {
+        assert(qemu_file_buffer_empty(param->file));
         len += save_page_header(pss, file, block, offset | RAM_SAVE_FLAG_ZERO);
         qemu_put_byte(file, 0);
         len += 1;
         ram_release_page(block->idstr, offset);
     } else if (param->result == RES_COMPRESS) {
+        assert(!qemu_file_buffer_empty(param->file));
         len += save_page_header(pss, file, block,
                                 offset | RAM_SAVE_FLAG_COMPRESS_PAGE);
         len += qemu_put_qemu_file(file, param->file);