Re: [lwip-users] TCP checksumming

[address@hidden]

Bill Auerbach schrieb:
> > Bill Auerbach wrote:
> >     
> > > One problem however: If I define LWIP_CHKSUM in my sys_arch.h,
> > > inet_chksum.c doesn't know about it. I had to add #include
> > > "sys_arch.h" to inet_chksum.c. In order to override LWIP_CHKSUM
> > > without changing source code, shouldn't include sys_arch.h?
> > >
> > >       
> > I don't think so: sys_arch.h is supposed to provide things needed for
> > the sys layer (like threads, mboxes and semaphores). When compiling with
> > NO_SYS=1, the whole stack should still be compilable without the whole
> > sys_arch.h file. You will have to put the definition somewhere else.
> >     
> OK.  I see.  This define (LWIP_CHKSUM) belongs in lwipopts.h not sys_arch.h
> as per the comment.  The question becomes where to put the prototype for the
> replacement function.  If it's in sys_arch.h to match sys_arch.c where the
> function definition is, then lwipopts.h or inet_chksum.c need sys_arch.h
> added to get the prototype pulled in.
>   
In my opinion, the comment is wrong. Also the place you want to put it 
seems wrong. The files sys_arch.c and sys_arch.h are supposed to be an 
architecture-dependent extension for sys.c. And sys.c's purpose is to 
provide OS abstraction functions. Like you already stated, the 
LWIP_CHKSUM function is needed regardless of the NO_SYS setting (in 
fact, that's what I meant in my last mail) so you have to put it 
somwhere else, not in sys_arch.c: sys.c and sys_arch.c don't have to be 
included in your build when compiling with NO_SYS=1!

You can just put the definition into cc.h or lwipopts.h and create your 
own c file with the function in it. And perhaps we should include an 
example in the contrib folder to clarify this for the future...?

Simon