block/migration: Disable cache invalidate for incoming migration

When migrated using libvirt with "--copy-storage-all", at the end of
migration there is race between NBD mirroring task trying to do flush
and migration completion, both end up invalidating cache. Since qcow2
driver does not handle this situation very well, random crashes happen.

This disables the BDRV_O_INCOMING flag for the block device being migrated
once the cache has been invalidated.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>

--

fixed parens by hand
Signed-off-by: Juan Quintela <quintela@redhat.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/nbd.c b/nbd.c
index e9b539be58..a7bce45117 100644
--- a/nbd.c
+++ b/nbd.c
@@ -972,6 +972,12 @@ NBDExport *nbd_export_new(BlockDriverState *bs, off_t dev_offset,
     exp->ctx = bdrv_get_aio_context(bs);
     bdrv_ref(bs);
     bdrv_add_aio_context_notifier(bs, bs_aio_attached, bs_aio_detach, exp);
+    /*
+     * NBD exports are used for non-shared storage migration.  Make sure
+     * that BDRV_O_INCOMING is cleared and the image is ready for write
+     * access since the export could be available before migration handover.
+     */
+    bdrv_invalidate_cache(bs, NULL);
     return exp;
 }