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Re: [Qemu-devel] [PATCH v5 22/45] postcopy: OS support test


From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH v5 22/45] postcopy: OS support test
Date: Mon, 30 Mar 2015 16:09:27 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0


On 30/03/2015 16:07, Dr. David Alan Gilbert wrote:
>>> > > 
>> > 
>> > 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.

I think it's okay.  First include syscall.h, then include
linux/userfaultfd.h under #ifdef.

> Although then what's the best way to tell people to try it out
> without an updated libc?

They don't need an updated libc, just an updated kernel.  syscall.h is
just a wrapper around Linux headers.

Paolo

> Or is it best to modify ./configure to detect it?



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