Re: [Qemu-devel] [Qemu-block] [PATCH v3] LUKS: support preallocation

[Max Reitz <mreitz@redhat.com>]

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On 15.07.19 10:30, Stefano Garzarella wrote:
> On Sun, Jul 14, 2019 at 05:51:51PM +0300, Maxim Levitsky wrote:
>> On Thu, 2019-07-11 at 18:27 +0200, Stefano Garzarella wrote:
>>> On Thu, Jul 11, 2019 at 06:09:40PM +0300, Maxim Levitsky wrote:
>>>> preallocation=off and preallocation=metadata
>>>> both allocate luks header only, and preallocation=falloc/full
>>>> is passed to underlying file.
>>>>
>>>> Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1534951
>>>>
>>>> Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
>>>>
>>>> ---
>>>>
>>>> Note that QMP support was only compile tested, since I am still learning
>>>> on how to use it.
>>>>
>>>> If there is some library/script/etc which makes it more high level,
>>>> I would more that glad to hear about it. So far I used the qmp-shell
>>>>
>>>> Also can I use qmp's blockdev-create outside a vm running?
>>>>
>>>>  block/crypto.c       | 29 ++++++++++++++++++++++++++---
>>>>  qapi/block-core.json |  5 ++++-
>>>>  2 files changed, 30 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/block/crypto.c b/block/crypto.c
>>>> index 8237424ae6..034a645652 100644
>>>> --- a/block/crypto.c
>>>> +++ b/block/crypto.c
>>>> @@ -74,6 +74,7 @@ static ssize_t block_crypto_read_func(QCryptoBlock *block,
>>>>  struct BlockCryptoCreateData {
>>>>      BlockBackend *blk;
>>>>      uint64_t size;
>>>> +    PreallocMode prealloc;
>>>>  };
>>>>  
>>>>  
>>>> @@ -112,7 +113,7 @@ static ssize_t block_crypto_init_func(QCryptoBlock *block,
>>>>       * available to the guest, so we must take account of that
>>>>       * which will be used by the crypto header
>>>>       */
>>>> -    return blk_truncate(data->blk, data->size + headerlen, PREALLOC_MODE_OFF,
>>>> +    return blk_truncate(data->blk, data->size + headerlen, data->prealloc,
>>>>                          errp);
>>>>  }
>>>>  
>>>> @@ -251,6 +252,7 @@ static int block_crypto_open_generic(QCryptoBlockFormat format,
>>>>  static int block_crypto_co_create_generic(BlockDriverState *bs,
>>>>                                            int64_t size,
>>>>                                            QCryptoBlockCreateOptions *opts,
>>>> +                                          PreallocMode prealloc,
>>>>                                            Error **errp)
>>>>  {
>>>>      int ret;
>>>> @@ -266,9 +268,14 @@ static int block_crypto_co_create_generic(BlockDriverState *bs,
>>>>          goto cleanup;
>>>>      }
>>>>  
>>>> +    if (prealloc == PREALLOC_MODE_METADATA) {
>>>> +        prealloc = PREALLOC_MODE_OFF;
>>>> +    }
>>>> +
>>>>      data = (struct BlockCryptoCreateData) {
>>>>          .blk = blk,
>>>>          .size = size,
>>>> +        .prealloc = prealloc,
>>>>      };
>>>>  
>>>>      crypto = qcrypto_block_create(opts, NULL,
>>>> @@ -500,6 +507,7 @@ block_crypto_co_create_luks(BlockdevCreateOptions *create_options, Error **errp)
>>>>      BlockdevCreateOptionsLUKS *luks_opts;
>>>>      BlockDriverState *bs = NULL;
>>>>      QCryptoBlockCreateOptions create_opts;
>>>> +    PreallocMode preallocation = PREALLOC_MODE_OFF;
>>>>      int ret;
>>>>  
>>>>      assert(create_options->driver == BLOCKDEV_DRIVER_LUKS);
>>>> @@ -515,8 +523,11 @@ block_crypto_co_create_luks(BlockdevCreateOptions *create_options, Error **errp)
>>>>          .u.luks = *qapi_BlockdevCreateOptionsLUKS_base(luks_opts),
>>>>      };
>>>>  
>>>> +    if (luks_opts->has_preallocation)
>>>> +        preallocation = luks_opts->preallocation;
>>>> +
>>>>      ret = block_crypto_co_create_generic(bs, luks_opts->size, &create_opts,
>>>> -                                         errp);
>>>> +                                         preallocation, errp);
>>>>      if (ret < 0) {
>>>>          goto fail;
>>>>      }
>>>> @@ -534,12 +545,24 @@ static int coroutine_fn block_crypto_co_create_opts_luks(const char *filename,
>>>>      QCryptoBlockCreateOptions *create_opts = NULL;
>>>>      BlockDriverState *bs = NULL;
>>>>      QDict *cryptoopts;
>>>> +    PreallocMode prealloc;
>>>> +    char *buf = NULL;
>>>>      int64_t size;
>>>>      int ret;
>>>> +    Error *local_err = NULL;
>>>>  
>>>>      /* Parse options */
>>>>      size = qemu_opt_get_size_del(opts, BLOCK_OPT_SIZE, 0);
>>>>  
>>>> +    buf = qemu_opt_get_del(opts, BLOCK_OPT_PREALLOC);
>>>> +    prealloc = qapi_enum_parse(&PreallocMode_lookup, buf,
>>>> +                               PREALLOC_MODE_OFF, &local_err);
>>>> +    g_free(buf);
>>>> +    if (local_err) {
>>>> +        error_propagate(errp, local_err);
>>>> +        return -EINVAL;
>>>> +    }
>>>> +
>>>>      cryptoopts = qemu_opts_to_qdict_filtered(opts, NULL,
>>>>                                               &block_crypto_create_opts_luks,
>>>>                                               true);
>>>> @@ -565,7 +588,7 @@ static int coroutine_fn block_crypto_co_create_opts_luks(const char *filename,
>>>>      }
>>>>  
>>>>      /* Create format layer */
>>>> -    ret = block_crypto_co_create_generic(bs, size, create_opts, errp);
>>>> +    ret = block_crypto_co_create_generic(bs, size, create_opts, prealloc, errp);
>>>>      if (ret < 0) {
>>>>          goto fail;
>>>>      }
>>>> diff --git a/qapi/block-core.json b/qapi/block-core.json
>>>> index 0d43d4f37c..ebcfc9f903 100644
>>>> --- a/qapi/block-core.json
>>>> +++ b/qapi/block-core.json
>>>> @@ -4205,13 +4205,16 @@
>>>>  #
>>>>  # @file             Node to create the image format on
>>>>  # @size             Size of the virtual disk in bytes
>>>> +# @preallocation    Preallocation mode for the new image (default: off;
>>>> +#                   allowed values: off/falloc/full
>>>
>>> Should we add also "metadata" to allowed values? and "since: 4.2"?
>>> I'd like to have (just to have similar documentation with others
>>> preallocation parameters):
>>
>> It it support but preallocation=off is the same as preallocation=metadata in luks,
>> as luks only metadata is the header which is created anyway.
>> In some sense I should throw a error for preallocation=off, but I suspect that
>> that will break userspace api.
>> What do you think?
> 
> I don't know very well the details, but I agree with you that some
> user APIs could expect that preallocation=off is always available.
> 
> Maybe we can write something in the comment (explaining that off and metadata
> are the same) and make the preallocation=metadata the default choice.

preallocation=off does not mean “Do not allocate any metadata”.  For
example, qcow2 still creates the qcow2 header and a minimal refcount
structure.  It just means not to allocate any unnecessary metadata.

For LUKS, all metadata is necessary, so preallocation=off and
preallocation=metadata are the same.  I don‘t think that means we only
need to support one or the other.  I think just making
preallocation=metadata an alias for preallocation=off here is fine – and
preallocation=off should stay the default, because it’s the default for
everything else.

Max


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