Re: [PATCH v2] socket: Implement sockaddr_storage with an anonymous union

[Alejandro Colomar <alx.manpages@gmail.com>]

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Hi Bastien,

On 1/20/23 21:32, Bastien Roucariès wrote:
[...]

>> diff --git a/bits/socket.h b/bits/socket.h
>> index aac8c49b00..c0c23b4e84 100644
>> --- a/bits/socket.h
>> +++ b/bits/socket.h
>> @@ -168,9 +168,14 @@ struct sockaddr
>>   
>>   struct sockaddr_storage
>>     {
>> -    __SOCKADDR_COMMON (ss_);	/* Address family, etc.  */
>> -    char __ss_padding[_SS_PADSIZE];
>> -    __ss_aligntype __ss_align;	/* Force desired alignment.  */
> no this is not correct you break ABI by reducing size
>> +    union
>> +      {
>> +        __SOCKADDR_COMMON (ss_);	/* Address family, etc.  */
>> +        struct sockaddr      sa;
>> +        struct sockaddr_in   sin;
>> +        struct sockaddr_in6  sin6;
>> +        struct sockaddr_un   sun;
>> +      };
>>     };
> 
> Correct one structure is
> 
> struct __private_sock_storage {
>      __SOCKADDR_COMMON (ssprivate_);   /* Address family, etc. */
>      char __ss_padding[_SS_PADSIZE];
>      __ss_aligntype __ss_align; /* Force desired alignment. */
> }

What is this structure for?  I expect that it's for declaring a wide-enough and 
correctly aligned type, but the union containing all the other types already 
guarantees a size as wide as any other sockaddr_* and with the widest alignment.

Also, any member that is necessary for superalignment or padding could be added 
at the end of sockaddr_storage, after the anon union; you don't need the extra 
struct, I guess.

Right?

> 
>   struct sockaddr_storage
>     {
>         union
>        {
>           __SOCKADDR_COMMON (ss_);       /* Address family, etc. */
>          struct sockaddr      sa;
>           struct sockaddr_in   sin;
>          struct sockaddr_in6  sin6;
>          struct sockaddr_un   sun;
>          struct __private_sock_storage _private;
>        };
> };
> 
> May it could be dropped later using align construct for modern C and padding
> 

Cheers,

Alex

> Bastien
>>   
>>   
>>
> 

-- 
<http://www.alejandro-colomar.es/>

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