Re: [PATCH v3 09/14] nbd/server: Initial support for extended headers

[Vladimir Sementsov-Ogievskiy]

On 15.05.23 22:53, Eric Blake wrote:
> Time to support clients that request extended headers.  Now we can
> finally reach the code added across several previous patches.
>
> Even though the NBD spec has been altered to allow us to accept
> NBD_CMD_READ larger than the max payload size (provided our response
> is a hole or broken up over more than one data chunk), we are not
> planning to take advantage of that, and continue to cap NBD_CMD_READ
> to 32M regardless of header size.
>
> For NBD_CMD_WRITE_ZEROES and NBD_CMD_TRIM, the block layer already
> supports 64-bit operations without any effort on our part.  For
> NBD_CMD_BLOCK_STATUS, the client's length is a hint, and the previous
> patch took care of implementing the required
> NBD_REPLY_TYPE_BLOCK_STATUS_EXT.
>
> Signed-off-by: Eric Blake <eblake@redhat.com>
> ---
>   nbd/nbd-internal.h |   5 +-

[..]

>   static inline void set_be_simple_reply(NBDClient *client, struct iovec *iov,
> -                                       uint64_t error, NBDRequest *request)
> +                                       uint32_t error, NBDStructuredError *err,
> +                                       NBDRequest *request)
>   {
> -    NBDSimpleReply *reply = iov->iov_base;
> +    if (client->header_style >= NBD_HEADER_EXTENDED) {
> +        NBDExtendedReplyChunk *chunk = iov->iov_base;
>
> -    iov->iov_len = sizeof(*reply);
> -    stl_be_p(&reply->magic, NBD_SIMPLE_REPLY_MAGIC);
> -    stl_be_p(&reply->error, error);
> -    stq_be_p(&reply->handle, request->handle);
> +        iov->iov_len = sizeof(*chunk);
> +        stl_be_p(&chunk->magic, NBD_EXTENDED_REPLY_MAGIC);
> +        stw_be_p(&chunk->flags, NBD_REPLY_FLAG_DONE);
> +        stq_be_p(&chunk->handle, request->handle);
> +        stq_be_p(&chunk->offset, request->from);
> +        if (error) {
> +            assert(!iov[1].iov_base);
> +            iov[1].iov_base = err;
> +            iov[1].iov_len = sizeof(*err);
> +            stw_be_p(&chunk->type, NBD_REPLY_TYPE_ERROR);
> +            stq_be_p(&chunk->length, sizeof(*err));
> +            stl_be_p(&err->error, error);
> +            stw_be_p(&err->message_length, 0);
> +        } else {
> +            stw_be_p(&chunk->type, NBD_REPLY_TYPE_NONE);
> +            stq_be_p(&chunk->length, 0);
> +        }
> +    } else {
> +        NBDSimpleReply *reply = iov->iov_base;
> +
> +        iov->iov_len = sizeof(*reply);
> +        stl_be_p(&reply->magic, NBD_SIMPLE_REPLY_MAGIC);
> +        stl_be_p(&reply->error, error);
> +        stq_be_p(&reply->handle, request->handle);
> +    }
>   }
>
>   static int coroutine_fn nbd_co_send_simple_reply(NBDClient *client,
> @@ -1906,30 +1966,44 @@ static int coroutine_fn 
> nbd_co_send_simple_reply(NBDClient *client,

So, that's not _simple_ now.. The function should be renamed. As well as set_be_simple_reply(). 
_simple_or_extended_ ? a bit too long. But continuing to use "simple" is in bad relation 
with use of "simple" word in specification.

Probably better to update callers? The only caller isi 
nbd_send_generic_reply(). So, could we just add 
nbd_co_send_single_extended_reply() to call from nbd_send_generic_reply() in 
case of EXTENDED?

Also, transformation of set_be_simple_reply() do look like it should be two 
separate functions.

>   {
>       NBDReply hdr;
>       int nbd_err = system_errno_to_nbd_errno(error);
> +    NBDStructuredError err;
>       struct iovec iov[] = {
>           {.iov_base = &hdr},
>           {.iov_base = data, .iov_len = len}
>       };
>
> +    assert(!len || !nbd_err);
>       trace_nbd_co_send_simple_reply(request->handle, nbd_err,
>                                      nbd_err_lookup(nbd_err), len);
> -    set_be_simple_reply(client, &iov[0], nbd_err, request);
> +    set_be_simple_reply(client, &iov[0], nbd_err, &err, request);
>
> -    return nbd_co_send_iov(client, iov, len ? 2 : 1, errp);
> +    return nbd_co_send_iov(client, iov, iov[1].iov_len ? 2 : 1, errp);
>   }
>
>   static inline void set_be_chunk(NBDClient *client, struct iovec *iov,
>                                   uint16_t flags, uint16_t type,
>                                   NBDRequest *request, uint32_t length)
>   {
> -    NBDStructuredReplyChunk *chunk = iov->iov_base;
> +    if (client->header_style >= NBD_HEADER_EXTENDED) {
> +        NBDExtendedReplyChunk *chunk = iov->iov_base;
>
> -    iov->iov_len = sizeof(*chunk);
> -    stl_be_p(&chunk->magic, NBD_STRUCTURED_REPLY_MAGIC);
> -    stw_be_p(&chunk->flags, flags);
> -    stw_be_p(&chunk->type, type);
> -    stq_be_p(&chunk->handle, request->handle);
> -    stl_be_p(&chunk->length, length);
> +        iov->iov_len = sizeof(*chunk);
> +        stl_be_p(&chunk->magic, NBD_EXTENDED_REPLY_MAGIC);
> +        stw_be_p(&chunk->flags, flags);
> +        stw_be_p(&chunk->type, type);
> +        stq_be_p(&chunk->handle, request->handle);
> +        stq_be_p(&chunk->offset, request->from);
> +        stq_be_p(&chunk->length, length);
> +    } else {
> +        NBDStructuredReplyChunk *chunk = iov->iov_base;
> +
> +        iov->iov_len = sizeof(*chunk);
> +        stl_be_p(&chunk->magic, NBD_STRUCTURED_REPLY_MAGIC);
> +        stw_be_p(&chunk->flags, flags);
> +        stw_be_p(&chunk->type, type);
> +        stq_be_p(&chunk->handle, request->handle);
> +        stl_be_p(&chunk->length, length);
> +    }
>   }
>
>   static int coroutine_fn nbd_co_send_structured_done(NBDClient *client,




--
Best regards,
Vladimir