From d9fef6139e17976db194d73848baff543c4a2590 Mon Sep 17 00:00:00 2001
From: Chuan Zheng <zhengchuan@huawei.com>
Date: Wed, 9 Feb 2022 08:49:41 +0800
Subject: [PATCH 10/15] migration: skip cache_drop for bios bootloader and
 nvram template

Qemu enabled page cache dropping for raw device on the destionation host
during shared storage migration.
However, fsync may take 300ms to multiple seconds to return in multiple-migration
scene, because all domains in a host share bios bootloader file, skip cache_drop
for bios bootloader and nvram template to avoid downtime increase.
---
 block.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/block.c b/block.c
index 0ac5b163d2..91f123a354 100644
--- a/block.c
+++ b/block.c
@@ -67,6 +67,9 @@
 
 #define NOT_DONE 0x7fffffff /* used while emulated sync operation in progress */
 
+#define DEFAULT_BIOS_BOOT_LOADER_DIR "/usr/share/edk2"
+#define DEFAULT_NVRAM_TEMPLATE_DIR "/var/lib/libvirt/qemu/nvram"
+
 static QTAILQ_HEAD(, BlockDriverState) graph_bdrv_states =
     QTAILQ_HEAD_INITIALIZER(graph_bdrv_states);
 
@@ -6432,7 +6435,13 @@ int coroutine_fn bdrv_co_invalidate_cache(BlockDriverState *bs, Error **errp)
             return ret;
         }
 
-        if (bs->drv->bdrv_co_invalidate_cache) {
+    /*
+     * It's not necessary for bios bootloader and nvram template to drop cache
+     * when migration, skip this step for them to avoid dowtime increase.
+     */
+        if (bs->drv->bdrv_co_invalidate_cache &&
+            !strstr(bs->filename, DEFAULT_BIOS_BOOT_LOADER_DIR) &&
+            !strstr(bs->filename, DEFAULT_NVRAM_TEMPLATE_DIR)) {
             bs->drv->bdrv_co_invalidate_cache(bs, &local_err);
             if (local_err) {
                 bs->open_flags |= BDRV_O_INACTIVE;
-- 
2.27.0