From: Hao Peng <peng.hao2@zte.com.cn>

At present shared disks can be migrated with either readonly or cache=none. But
cache=directsync should be safe for migration, because both cache=directsync and cache=none
don't use the host page cache, and cache=direct write through qemu block layer cache.

Signed-off-by: Peng Hao <peng.hao2@zte.com.cn>
Reviewed-by: Wang Yechao <wang.yechao255@zte.com.cn>
---
 src/qemu/qemu_migration.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/src/qemu/qemu_migration.c b/src/qemu/qemu_migration.c
index c23fffe..9d509dd 100644
--- a/src/qemu/qemu_migration.c
+++ b/src/qemu/qemu_migration.c
@@ -1160,11 +1160,12 @@ qemuMigrationIsSafe(virDomainDefPtr def,
         const char *src = virDomainDiskGetSource(disk);
 
         /* Our code elsewhere guarantees shared disks are either readonly (in
-         * which case cache mode doesn't matter) or used with cache=none */
+         * which case cache mode doesn't matter) or used with cache=none or used with cache=directsync */
         if (virStorageSourceIsEmpty(disk->src) ||
             disk->src->readonly ||
             disk->src->shared ||
-            disk->cachemode == VIR_DOMAIN_DISK_CACHE_DISABLE)
+            disk->cachemode == VIR_DOMAIN_DISK_CACHE_DISABLE ||
+            disk->cachemode == VIR_DOMAIN_DISK_CACHE_DIRECTSYNC)
             continue;
 
         /* disks which are migrated by qemu are safe too */
@@ -1188,7 +1189,7 @@ qemuMigrationIsSafe(virDomainDefPtr def,
 
         virReportError(VIR_ERR_MIGRATE_UNSAFE, "%s",
                        _("Migration may lead to data corruption if disks"
-                         " use cache != none"));
+                         " use cache != none or cache != directsync"));
         return false;
     }
 
-- 
1.8.3.1


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On Sat, Jul 15, 2017 at 11:01:25PM +0800, Peng Hao wrote:
> From: Hao Peng <peng.hao2@zte.com.cn>
> 
> At present shared disks can be migrated with either readonly or cache=none. But
> cache=directsync should be safe for migration, because both cache=directsync and cache=none
> don't use the host page cache, and cache=direct write through qemu block layer cache.
> 
> Signed-off-by: Peng Hao <peng.hao2@zte.com.cn>
> Reviewed-by: Wang Yechao <wang.yechao255@zte.com.cn>
> ---
>  src/qemu/qemu_migration.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)

Reviewed-by: Daniel P. Berrange <berrange@redhat.com>

and pushed to git master

Regards,
Daniel
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