Re: [Qemu-devel] [PATCH 0/5] block/qcow2-bitmap: Enable resize with persistent bitmaps

[John Snow]

On 3/5/19 6:43 PM, John Snow wrote:

++ This series relies on [Qemu-devel] [PATCH v3 0/7] bitmaps: add
inconsistent bit, you can apply it on top of those patches, or you can
use my github staging branch as a basis:

https://github.com/jnsnow/qemu/tree/bitmaps

> This series aims to enable block resizes when persistent bitmaps are
> in use. The basic approach here is to recognize that we now load all
> persistent bitmaps in memory, and so we can rely on in-memory resizes
> and then flush the changed metadata back to disk.
> 
> One part that is potentially now quite strange is that bitmap resizes
> may happen twice: once during the qcow2 resize event only if persistent
> bitmaps are found, and then again as part of the generic resize callback
> event whether or not we have any persistent bitmaps.
> 
> The second round is required if we are not using qcow2 or we have only
> transient bitmaps. The first round is required as we wish to flush the
> bitmaps back to disk atomically with the qcow2 resize to avoid violating
> our invariants for the bitmap metadata which is checked in many places.
> 
> This is harmless; hbitmap_truncate will recognize the second round as
> a no-op.
> 
> John Snow (5):
>   block/qcow2-bitmap: Skip length check in some cases
>   block/qcow2-bitmap: Allow bitmap flushing
>   block/qcow2-bitmap: don't remove bitmaps on reopen
>   block/qcow2-bitmap: Allow resizes with persistent bitmaps
>   tests/qemu-iotests: add bitmap resize test 246
> 
>  block/qcow2.h              |   2 +
>  block/qcow2-bitmap.c       | 123 +++++++++++----
>  block/qcow2.c              |  27 +++-
>  tests/qemu-iotests/246     | 114 ++++++++++++++
>  tests/qemu-iotests/246.out | 296 +++++++++++++++++++++++++++++++++++++
>  tests/qemu-iotests/group   |   1 +
>  6 files changed, 528 insertions(+), 35 deletions(-)
>  create mode 100755 tests/qemu-iotests/246
>  create mode 100644 tests/qemu-iotests/246.out
>