On Fri, Oct 20, 2000 at 10:47:45AM -0700, Linus Torvalds wrote:
> On Fri, 20 Oct 2000, Philipp Rumpf wrote:
> >
> > Single Unix specifies that 0-byte reads, as well as 0-byte writes, should
> > "return 0 and have no other results". Our current implementation violates
> > the first requirement and makes it very easy to violate the second one.
>
> Note that there _are_ cases where 0-byte reads and writes have specific
> meaning, notably there are some networking things where a 0-byte sendto()
> does something special if I remember correctly. And I seem to remember
> that this also _did_ translate into write().
sock_write and sock_read contain:
if(size==0) /* Match SYS5 behaviour */
return 0;
I'm not sure which other read()/write() functions are used by
"networking things", but I don't see any others sendto would map to.
So I suspect if there are any applications which would need the behaviour
you described they've already been broken, and should be recompiled to use
sys_send(|to|msg) (via sys_socketcall on x86, of course).
> I remember that Linux used to do exactly this, and we had to pass the
> 0-byte writes into the low-level cases exactly because some low-level
> cases do care.
I would suspect most of those have been eliminated by now.
> I suspect SUS only talks about regular files.
As I'm reading it, they're talking about every read() call, even those with
an invalid fd.
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