Re: [Qemu-devel] [virtio-dev] [PATCH v18 1/2] virtio-crypto: Add virtio crypto device specification

[Halil Pasic <pasic@linux.vnet.ibm.com>]

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On 05/16/2017 05:33 PM, Stefan Hajnoczi wrote:
> On Sat, Apr 22, 2017 at 02:23:50PM +0800, Gonglei wrote:
>> +Dataq requests for both session and stateless modes are as follows:
>> +
>> +\begin{lstlisting}
>> +struct virtio_crypto_op_data_req_mux {
>> +    struct virtio_crypto_op_header header;
>> +
>> +    union {
>> +        struct virtio_crypto_sym_data_req   sym_req;
>> +        struct virtio_crypto_hash_data_req  hash_req;
>> +        struct virtio_crypto_mac_data_req   mac_req;
>> +        struct virtio_crypto_aead_data_req  aead_req;
>> +        struct virtio_crypto_sym_data_req_stateless   sym_stateless_req;
>> +        struct virtio_crypto_hash_data_req_stateless  hash_stateless_req;
>> +        struct virtio_crypto_mac_data_req_stateless   mac_stateless_req;
>> +        struct virtio_crypto_aead_data_req_stateless  aead_stateless_req;
>> +    } u;
>> +};
>> +\end{lstlisting}
> 
> Halil touched on this in the discussion: this spec uses a C-like struct
> syntax but does not define whether unions really affect sizeof(mystruct)
> like they would in C or whether you just mean that any of the union
> fields can be used.  This distinction is important so device and driver
> authors understand the exact memory layout of requests and responses.
> 
> Please include an explanation about the meaning of "union" in the text.
> 

I do not think simple explaining the union will do. I think this
description is bleeding from more wounds. I tried to explain this
while reviewing the implementation here:
https://lists.gnu.org/archive/html/qemu-devel/2017-05/msg03876.html

Unfortunately some technical issues precluded me from posting it
in a timely manner.

@Stefan: Thanks for joining the discussion.

Regards,
Halil


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