Re: [Qemu-devel] [PATCH] qcow2: Restore total_sectors value in save_vmstate

[Eric Blake <eblake@redhat.com>]

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On 10/20/2013 07:28 PM, Max Reitz wrote:
> Since df2a6f29a5, bdrv_co_do_writev increases the total_sectors value of
> a growable block devices on writes after the current end. This leads to
> the virtual disk apparently growing in qcow2_save_vmstate, which in turn
> affects the disk size captured by the internal snapshot taken directly
> afterwards through e.g. the HMP savevm command. Such a "grown" snapshot
> cannot be loaded after reopening the qcow2 image, since its disk size
> differs from the actual virtual disk size (writing a VM state does not
> actually increase the virtual disk size).
> 
> Fix this by restoring total_sectors at the end of qcow2_save_vmstate.
> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>  block/qcow2.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 

> @@ -1946,6 +1947,10 @@ static int qcow2_save_vmstate(BlockDriverState *bs, QEMUIOVector *qiov,
>      bs->growable = 1;
>      ret = bdrv_pwritev(bs, qcow2_vm_state_offset(s) + pos, qiov);
>      bs->growable = growable;
> +    // bdrv_co_do_writev will have increased the total_sectors value to include
> +    // the VM state - the VM state is however not an actual part of the block
> +    // device, therefore, we need to restore the old value.
> +    bs->total_sectors = total_sectors;

It looks like // comments aren't forbidden, but also uncommon; I don't
know if /**/ would be better.  At any rate:

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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