Re: [Question] New mmap64 syscall?

Yury Norov
2016-12-07T15:48:11Z

On Wed, Dec 07, 2016 at 02:23:55PM +0100, Florian Weimer wrote:
> On 12/06/2016 07:54 PM, Yury Norov wrote:
> >3. Introduce new mmap64() syscall like this:
> >sys_mmap64(void *addr, size_t len, int prot, int flags, int fd, struct off_pair *off);
> >(The pointer here because otherwise we have 7 args, if simply pass off_hi and
> >off_lo in registers.)
>
> I would prefer a batched mmap/munmap/mremap/mprotect/madvise interface, so
> that VM changes can be coalesced and the output reduced. This interface
> could then be used to implement mmap on 32-bit architectures as well because
> the offset restrictions would not apply there.

Hi Florian,

I frankly don't understand what you mean, All syscalls you mentioned
doesn't take off_t or other 64-bit arguments. 'VM changes' - virtual
memory? If so, I don't see any changes in VM with this approach, just
correct handling of big offsets.

> This interface
> could then be used to implement mmap on 32-bit architectures as well

This is for 32-bit architectures only. 64 bit arches use
sysdeps/unix/sysv/linux/wordsize-64/mmap.c for both mmap and mmap64,
and they don't need that tricks with off_t. Or you meaning to switch
64-bit mmap to this interface?

Please explain what you mean in details.

Yury