migration/xbzrle: update cache and current_data in one place

When we are not in the last_stage, we need to update the cache if page
is not the same.

Currently this procedure is scattered in two places and mixed with
encoding status check.

This patch extract this general step out to make the code a little bit
easy to read.

Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20190610004159.20966-1-richardw.yang@linux.intel.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

1 files changed, 15 insertions, 10 deletions

diff --git a/migration/ram.c b/migration/ram.c
index 74c9306..d3d72b6 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -1585,25 +1585,30 @@ static int save_xbzrle_page(RAMState *rs, uint8_t **current_data,
     encoded_len = xbzrle_encode_buffer(prev_cached_page, XBZRLE.current_buf,
                                        TARGET_PAGE_SIZE, XBZRLE.encoded_buf,
                                        TARGET_PAGE_SIZE);
+
+    /*
+     * Update the cache contents, so that it corresponds to the data
+     * sent, in all cases except where we skip the page.
+     */
+    if (!last_stage && encoded_len != 0) {
+        memcpy(prev_cached_page, XBZRLE.current_buf, TARGET_PAGE_SIZE);
+        /*
+         * In the case where we couldn't compress, ensure that the caller
+         * sends the data from the cache, since the guest might have
+         * changed the RAM since we copied it.
+         */
+        *current_data = prev_cached_page;
+    }
+
     if (encoded_len == 0) {
         trace_save_xbzrle_page_skipping();
         return 0;
     } else if (encoded_len == -1) {
         trace_save_xbzrle_page_overflow();
         xbzrle_counters.overflow++;
-        /* update data in the cache */
-        if (!last_stage) {
-            memcpy(prev_cached_page, *current_data, TARGET_PAGE_SIZE);
-            *current_data = prev_cached_page;
-        }
         return -1;
     }
 
-    /* we need to update the data in the cache, in order to get the same data */
-    if (!last_stage) {
-        memcpy(prev_cached_page, XBZRLE.current_buf, TARGET_PAGE_SIZE);
-    }
-
     /* Send XBZRLE based compressed page */
     bytes_xbzrle = save_page_header(rs, rs->f, block,
                                     offset | RAM_SAVE_FLAG_XBZRLE);