Re: [Question] New mmap64 syscall?

From: Florian Weimer
Date: Thu Dec 08 2016 - 10:54:15 EST

On 12/07/2016 04:48 PM, Yury Norov wrote:
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.

What I was trying to suggest is a completely different interface which is not subject to register size constraints and which has been requested before (a mechanism for batching mm updates).