Re: [libvirt] [PATCH RESEND] qemu: shared disks with cache=directsync should be safe for migration

[Daniel P. Berrange]

On Sat, Jul 15, 2017 at 11:01:25PM +0800, Peng Hao wrote:
> From: Hao Peng 
> 
> 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 
> Reviewed-by: Wang Yechao 
> ---
>  src/qemu/qemu_migration.c | 7 ---
>  1 file changed, 4 insertions(+), 3 deletions(-)

Reviewed-by: Daniel P. Berrange 

and pushed to git master

Regards,
Daniel
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[libvirt] [PATCH RESEND] qemu: shared disks with cache=directsync should be safe for migration

[Peng Hao]

From: Hao Peng 

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 
Reviewed-by: Wang Yechao 
---
 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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