Re: [Qemu-block] [PATCH] block: implement the bdrv_reopen_prepare helper for LUKS driver

[Max Reitz]

On 2018-01-18 11:31, Daniel P. Berrange wrote:
> If the bdrv_reopen_prepare helper isn't provided, the qemu-img commit
> command fails to re-open the base layer after committing changes into
> it. Provide a no-op implementation for the LUKS driver, since there
> is not any custom work that needs doing to re-open it.
> 
> Signed-off-by: Daniel P. Berrange <address@hidden>
> ---
>  block/crypto.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/block/crypto.c b/block/crypto.c
> index 60ddf8623e..bb9a8f5376 100644
> --- a/block/crypto.c
> +++ b/block/crypto.c
> @@ -382,6 +382,12 @@ static void block_crypto_close(BlockDriverState *bs)
>      qcrypto_block_free(crypto->block);
>  }
>  
> +static int block_crypto_reopen_prepare(BDRVReopenState *state,
> +                                       BlockReopenQueue *queue, Error **errp)
> +{
> +    /* nothing needs checking */
> +    return 0;
> +}

Unfortunately I have to admit I'm not quite an expert on reopen
myself...  But generally it is used to change options, so in theory one
could provide a new key-secret here.  It's up to you whether you want to
support that or not (with this implementation the user will get an error
when they want to change the key-secret).

Apart from that, I think a no-op should be OK.

Max

>  
>  /*
>   * 1 MB bounce buffer gives good performance / memory tradeoff
> @@ -620,6 +626,7 @@ BlockDriver bdrv_crypto_luks = {
>      .bdrv_truncate      = block_crypto_truncate,
>      .create_opts        = &block_crypto_create_opts_luks,
>  
> +    .bdrv_reopen_prepare = block_crypto_reopen_prepare,
>      .bdrv_refresh_limits = block_crypto_refresh_limits,
>      .bdrv_co_preadv     = block_crypto_co_preadv,
>      .bdrv_co_pwritev    = block_crypto_co_pwritev,
>

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