> I've a problem with -Wcast-qual: [...a writev-style use of struct
> iovec...]

Yes.  struct iovec, in write-style uses, is incompatible with proper
const poisoning (not terribly surprising, since it predates const).
The const-clean way is to have a constified version which is used by
write-style calls and a non-constified version for read-style or
read/write calls - but that is difficult for backward-compatability
reasons.

Personally, I just strip the qualifiers, typically with something like

void *dequal(const volatile void *arg)
{
 return(((const volatile char *)arg)-(const volatile char *)0)+(char *)0);
}

which is not really portable, but close enough for me.  (To be properly
portable you'd have to do something like

void *dequal(const volatile void *arg)
{
 void *rv;

 bcopy(&arg,&rv,sizeof(void *));
 return(rv);
}

but I usually don't think calling the external routine is worth the
additional portability, even if it does get inlined at least some of
the time.  The __UNCONST christos recommended involves another
nonportability, at least in its 3.0 implementation, namely that
assuming that casting to unsigned long and back doesn't destroy
information; I may start using that myself, since I suspect that's at
least as portable as the arithmetic-on-nil-pointers way.)

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