linux-kernel - Re: [Question] New mmap64 syscall?

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Date:   Wed, 7 Dec 2016 21:18:11 +0530
From:   Yury Norov <ynorov@...iumnetworks.com>
To:     Florian Weimer <fweimer@...hat.com>
CC:     <libc-alpha@...rceware.org>, <linux-arch@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        <szabolcs.nagy@....com>, <heiko.carstens@...ibm.com>,
        <cmetcalf@...hip.com>, <philipp.tomsich@...obroma-systems.com>,
        <joseph@...esourcery.com>, <zhouchengming1@...wei.com>,
        <Prasun.Kapoor@...iumnetworks.com>, <agraf@...e.de>,
        <geert@...ux-m68k.org>, <kilobyte@...band.pl>,
        <manuel.montezelo@...il.com>, <arnd@...db.de>, <pinskia@...il.com>,
        <linyongting@...wei.com>, <klimov.linux@...il.com>,
        <broonie@...nel.org>, <bamvor.zhangjian@...wei.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <maxim.kuvyrkov@...aro.org>, <Nathan_Lynch@...tor.com>,
        <schwidefsky@...ibm.com>, <davem@...emloft.net>,
        <christoph.muellner@...obroma-systems.com>
Subject: Re: [Question] New mmap64 syscall?

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