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Re: [Qemu-devel] [PATCH v5 22/45] postcopy: OS support test
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [PATCH v5 22/45] postcopy: OS support test |
Date: |
Mon, 30 Mar 2015 15:07:49 +0100 |
User-agent: |
Mutt/1.5.23 (2014-03-12) |
* Paolo Bonzini (address@hidden) wrote:
>
>
> On 13/03/2015 11:41, Dr. David Alan Gilbert wrote:
> >>> > > +#ifdef HOST_X86_64
> >>> > > +#ifndef __NR_userfaultfd
> >>> > > +#define __NR_userfaultfd 323
> >> >
> >> > Sholdn't this come from the kernel headers imported in the previous
> >> > patch? Rather than having an arch-specific hack.
> > The header, like the rest of the kernel headers, just provides
> > the constant and structure definitions for the call; the syscall numbers
> > come from arch specific headers. I guess in the final world I wouldn't
> > need this at all since it'll come from the system headers; but what's
> > the right way to put this in for new syscalls?
> >
>
> You would just require new _installed_ kernel headers. Then you can use
> linux/userfaultfd.h and syscall.h (the latter from glibc, includes
> asm/unistd.h to get syscall numbers).
>
> linux-headers/ is useful for APIs that do not require system calls, or
> for APIs that are extensible. However, if a system call is required
> (and mandatory) it's simpler to just use installed headers.
OK, so then I could check for ifdef __NR_userfault and then
do the include and I think that would be safe.
Although then what's the best way to tell people to try it out
without an updated libc?
Or is it best to modify ./configure to detect it?
Dave
>
> Paolo
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK