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Re: [Qemu-block] [PATCH 09/22] block: introduce persistent dirty bitmaps

From: Vladimir Sementsov-Ogievskiy
Subject: Re: [Qemu-block] [PATCH 09/22] block: introduce persistent dirty bitmaps
Date: Wed, 12 Oct 2016 14:38:30 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0

On 07.10.2016 22:28, Max Reitz wrote:
On 30.09.2016 12:53, Vladimir Sementsov-Ogievskiy wrote:
New field BdrvDirtyBitmap.persistent means, that bitmap should be saved
on bdrv_close, using format driver. Format driver should maintain bitmap

Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
  block.c                      | 30 ++++++++++++++++++++++++++++++
  block/dirty-bitmap.c         | 27 +++++++++++++++++++++++++++
  block/qcow2-bitmap.c         |  1 +
  include/block/block.h        |  2 ++
  include/block/block_int.h    |  2 ++
  include/block/dirty-bitmap.h |  6 ++++++
  6 files changed, 68 insertions(+)

diff --git a/block/dirty-bitmap.c b/block/dirty-bitmap.c
index 623e1d1..0314581 100644
--- a/block/dirty-bitmap.c
+++ b/block/dirty-bitmap.c

@@ -555,3 +559,26 @@ bool bdrv_dirty_bitmap_get_autoload(const BdrvDirtyBitmap 
      return bitmap->autoload;
+void bdrv_dirty_bitmap_set_persistance(BdrvDirtyBitmap *bitmap,
+                                                bool persistent)
+    bitmap->persistent = persistent;
After some thinking, I think this function should be more complex: It
should check whether the node the bitmap is attached to actually can
handle persistent bitmaps and whether it would actually support storing
*this* bitmap.

For instance, a qcow2 node would not support writing overly large
bitmaps (limited by BME_MAX_TABLE_SIZE and BME_MAX_PHYS_SIZE) or bitmaps
with overly large granularities (BME_MAX_GRANULARITY_BITS) or bitmaps
whose name is already occupied by some bitmap that is already stored in
the file but has not been loaded.

Checking this here will trivially prevent users from creating such
bitmaps and will also preempt detection of such failures during
bdrv_close() when they cannot be handled gracefully.


Good point, but I can't do it exactly as you say, because I call this function from qcow2_read_bitmaps, for just created bitmap and it should not be checked and of course it's name is occupied..


Best regards,

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