Date: Mon, 22 Apr 2002 23:13:29 -0400 From: Kenneth Culver <culverk@yumyumyum.org> To: Andrew Gallatin <gallatin@cs.duke.edu> Cc: freebsd-hackers@freebsd.org, freebsd-emulation@freebsd.org Subject: Re: implementing linux mmap2 syscall Message-ID: <200204222313.29181.culverk@yumyumyum.org> In-Reply-To: <15556.6399.62081.426193@grasshopper.cs.duke.edu> References: <200204211525.08827.culverk@yumyumyum.org> <15556.6399.62081.426193@grasshopper.cs.duke.edu>
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On Monday 22 April 2002 10:06 am, you wrote:
> Kenneth Culver writes:
> > static inline unsigned long do_mmap(struct file *file, unsigned long
> > addr,
>
> <..>
>
> > =09=09ret =3D do_mmap_pgoff(file, addr, len, prot, flag, offset >>
> > PAGE_SHIFT); out:
> > =09return ret;
> > }
> >
> > This is what mmap2 does:
> >
> > andstatic inline long do_mmap2(
> > =09unsigned long addr, unsigned long len,
> > =09unsigned long prot, unsigned long flags,
> > =09unsigned long fd, unsigned long pgoff)
>
> <...>
>
> > =09error =3D do_mmap_pgoff(file, addr, len, prot, flags, pgoff);
> >
> >
> > So what it looks like to me is that mmap2 expects an offset that's
> > already page-aligned (I'm not sure if this is the right way to say i=
t),
> > where mmap doesn't. the FreeBSD code in the linuxulator basically ju=
st
> > takes the offset
>
> To me, it looks like mmap2 takes an offset that's a page index, rather
> than a byte position. Since linux passes the offset with a 32-bit
> long, rather than a 64-bit off_t like we do, they need to do this in
> order to be able to map offsets larger than 4GB into a file.
>
> For linux_mmap2, I'd think we want to do roughly the same things as
> linux_mmap, but with bsd_args.pos =3D ctob((off_t)linux_args.pos)
>
> Drew
OK, I found another problem, here it is:
static void
linux_prepsyscall(struct trapframe *tf, int *args, u_int *code, caddr_t=20
*params)
{
=09args[0] =3D tf->tf_ebx;
=09args[1] =3D tf->tf_ecx;
=09args[2] =3D tf->tf_edx;
=09args[3] =3D tf->tf_esi;
=09args[4] =3D tf->tf_edi;
=09*params =3D NULL;=09=09/* no copyin */
}
Basically, linux_mmap2 takes 6 args, and this looks here like only 5 args=
are=20
making it in... I checked this because the sixth argument to linux_mmap2(=
) in=20
truss was showing 0x6, but when I printed out that arg from the kernel, i=
t=20
was showing 0x0. Am I correct here?
Ken
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