Re: [PATCH 7/8] hw/9pfs: annotate V9fsTransport callbacks as coroutine_fn

On 20/7/26 16:02, Christian Schoenebeck wrote:
> On Monday, 20 July 2026 09:55:36 CEST Marc-André Lureau wrote:
>> All V9fsTransport callbacks are invoked exclusively from coroutine
>> context (the v9fs_* PDU handlers). Annotate the function pointer
>> types in V9fsTransport and all implementations (virtio and xen
>> backends), as well as intermediate callers in 9p.c (pdu_marshal,
>> pdu_unmarshal, v9fs_init_qiov_from_pdu, etc.).
>>
>> Signed-off-by: Marc-André Lureau <[email protected]>
>> ---
>>   hw/9pfs/9p.h               | 26 +++++++++++++++-----------
>>   hw/9pfs/9p.c               | 31 +++++++++++++++++++------------
>>   hw/9pfs/virtio-9p-device.c | 24 +++++++++++++-----------
>>   hw/9pfs/xen-9p-backend.c   | 34 +++++++++++++++++-----------------
>>   4 files changed, 64 insertions(+), 51 deletions(-)
>>
>> diff --git a/hw/9pfs/9p.h b/hw/9pfs/9p.h
>> index 1a309664f6e..0e52ffbdf38 100644
>> --- a/hw/9pfs/9p.h
>> +++ b/hw/9pfs/9p.h
>> @@ -472,17 +472,21 @@ void pdu_submit(V9fsPDU *pdu, P9MsgHeader *hdr);
>>   void v9fs_reset(V9fsState *s);
>>
>>
>>   struct V9fsTransport {
>> -    ssize_t     (*pdu_vmarshal)(V9fsPDU *pdu, size_t offset, const char *fmt,
>> -                                va_list ap);
>> -    ssize_t     (*pdu_vunmarshal)(V9fsPDU *pdu, size_t offset, const char *fmt,
>> -                                  va_list ap);
>> -    void        (*init_in_iov_from_pdu)(V9fsPDU *pdu, struct iovec **piov,
>> -                                        unsigned int *pniov, size_t size);
>> -    void        (*init_out_iov_from_pdu)(V9fsPDU *pdu, struct iovec **piov,
>> -                                         unsigned int *pniov, size_t size);
>> -    void        (*push_and_notify)(V9fsPDU *pdu);
>> -    size_t      (*msize_limit)(V9fsState *s);
>> -    size_t      (*response_buffer_size)(V9fsPDU *pdu);
>> +    ssize_t     coroutine_fn (*pdu_vmarshal)(V9fsPDU *pdu, size_t offset,
>> +                                             const char *fmt, va_list ap);
>> +    ssize_t     coroutine_fn (*pdu_vunmarshal)(V9fsPDU *pdu, size_t offset,
>> +                                               const char *fmt, va_list ap);
>> +    void        coroutine_fn (*init_in_iov_from_pdu)(V9fsPDU *pdu,
>> +                                                     struct iovec **piov,
>> +                                                     unsigned int *pniov,
>> +                                                     size_t size);
>> +    void        coroutine_fn (*init_out_iov_from_pdu)(V9fsPDU *pdu,
>> +                                                      struct iovec **piov,
>> +                                                      unsigned int *pniov,
>> +                                                      size_t size);
>> +    void        coroutine_fn (*push_and_notify)(V9fsPDU *pdu);
>> +    size_t      coroutine_fn (*msize_limit)(V9fsState *s);
>> +    size_t      coroutine_fn (*response_buffer_size)(V9fsPDU *pdu);
>>   };
> 
> I wonder whether that could be made more diff/blame-friendly. Especially as
> this currently only serves documentation purposes.
> 
> They way you are positioning coroutine_fn it usually resolves to an attribute
> attached to the function's return type, not to the function itself, even
> though clang/gcc handling it flexible. For attaching an attribute to the
> function itself the attribute should either be attached before the function
> declaration or after the function declaration.

I tend to aggree it would be clearer to have these attributes /before/
the function prototype declaration.

> In both cases you could then
> add it to its own, separate line, avoiding a lot of noise.
> 
> /Christian
> 
> 
> 
>