[Qemu-devel] [PULL 07/15] migration: fix incorrect bitmap size calculation

["Dr. David Alan Gilbert (git)" <dgilbert@redhat.com>]

From: Peter Xu <peterx@redhat.com>

The calculation on size of received bitmap is incorrect for postcopy
recovery.  Here we wanted to let the size to cover all the valid bits in
the bitmap, we should use DIV_ROUND_UP() instead of a division.

For example, a RAMBlock with size=4K (which contains only one single 4K
page) will have nbits=1, then nbits/8=0, then the real bitmap won't be
sent to source at all.

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20180710091902.28780-4-peterx@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
---
 migration/ram.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/migration/ram.c b/migration/ram.c
index 49068e86d3..52dd678092 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -235,7 +235,7 @@ int64_t ramblock_recv_bitmap_send(QEMUFile *file,
     bitmap_to_le(le_bitmap, block->receivedmap, nbits);
 
     /* Size of the bitmap, in bytes */
-    size = nbits / 8;
+    size = DIV_ROUND_UP(nbits, 8);
 
     /*
      * size is always aligned to 8 bytes for 64bit machines, but it
@@ -3944,7 +3944,7 @@ int ram_dirty_bitmap_reload(MigrationState *s, RAMBlock *block)
     int ret = -EINVAL;
     QEMUFile *file = s->rp_state.from_dst_file;
     unsigned long *le_bitmap, nbits = block->used_length >> TARGET_PAGE_BITS;
-    uint64_t local_size = nbits / 8;
+    uint64_t local_size = DIV_ROUND_UP(nbits, 8);
     uint64_t size, end_mark;
 
     trace_ram_dirty_bitmap_reload_begin(block->idstr);
-- 
2.17.1