Re: [Qemu-devel] [PATCH 02/02] linux-user : add vmsplice system call

[Riku Voipio]

On Mon, May 25, 2009 at 11:43:07AM +0530, vibi sreenivasan wrote:
> hi,
>       Thanks for your comment.
> > fine that you provide missing syscalls for user mode one after the other.
> > 
> > I have one remark: if the host os kernel is too old to provide the
> > syscalls, they should be #if'ed out (tee, vmsplice & co).
> if the host kernel is too old , i think it will return -1 & set errno to
> ENOSYS.
> So isnt that same as putting #ifdef.

Yes, having old kernel is not a problem in this. However, having a
old libc when compiling qemu can be a problem. Think Redhat RHEL 4
or debian etch. vmsplice() is not available, and compiling qemu
would fail.

See how we #ifdef utimensat in linux-user/syscall.c and detect
availability in ./configure

Other than that, your patches looked ok.
 
> > Or even emulate the syscall - which can be quite hard.

> Hmm thinking on that. will it be worth?

This could be in interest for people who want to run qemu linux-user
on non-linux systems (such a *bsd). But that doesn't work yet,
and even when people get it working, new syscalls such as tee/splice
are not the most important ones to provide emulation for. Very
few applications use these syscalls yet.