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Re: [Question] New mmap64 syscall?
- From: Dr. Philipp Tomsich <philipp dot tomsich at theobroma-systems dot com>
- To: Yury Norov <ynorov at caviumnetworks dot com>
- Cc: Arnd Bergmann <arnd at arndb dot de>, libc-alpha at sourceware dot org, linux-arch at vger dot kernel dot org, LKML <linux-kernel at vger dot kernel dot org>, Catalin Marinas <catalin dot marinas at arm dot com>, szabolcs dot nagy at arm dot com, heiko dot carstens at de dot ibm dot com, cmetcalf at ezchip dot com, "Joseph S. Myers" <joseph at codesourcery dot com>, zhouchengming1 at huawei dot com, "Kapoor, Prasun" <Prasun dot Kapoor at caviumnetworks dot com>, Alexander Graf <agraf at suse dot de>, geert at linux-m68k dot org, kilobyte at angband dot pl, manuel dot montezelo at gmail dot com, Andrew Pinski <pinskia at gmail dot com>, linyongting at huawei dot com, Alexey Klimov <klimov dot linux at gmail dot com>, broonie at kernel dot org, "Zhangjian (Bamvor)" <bamvor dot zhangjian at huawei dot com>, linux-arm-kernel <linux-arm-kernel at lists dot infradead dot org>, Maxim Kuvyrkov <maxim dot kuvyrkov at linaro dot org>, Nathan_Lynch at mentor dot com, schwidefsky at de dot ibm dot com, davem at davemloft dot net, christoph dot muellner at theobroma-systems dot com
- Date: Wed, 7 Dec 2016 12:07:24 +0100
- Subject: Re: [Question] New mmap64 syscall?
- Authentication-results: sourceware.org; auth=none
- References: <20161206185440.GA4654@yury-N73SV> <3014428.VXGdOARdm1@wuerfel> <20161207103451.GA869@yury-N73SV>
[Resend, as my mail-client had insisted on using the wrong MIME type…]
> On 07 Dec 2016, at 11:34, Yury Norov <ynorov@caviumnetworks.com> wrote:
>
>> If there is a use case for larger than 16TB offsets, we should add
>> the call on all architectures, probably using your approach 3. I don't
>> think that we should treat it as anything special for arm64 though.
>
> From this point of view, 16+TB offset is a matter of 16+TB storage,
> and it's more than real. The other consideration to add it is that
> we have 64-bit support for offsets in syscalls like sys_llseek().
> So mmap64() will simply extend this support.
I believe the question is rather if the 16TB offset is a real use-case for ILP32. This
seems to bring the discussion full-circle, as this would indicate that 64bit is the
preferred bit-width for all sizes, offsets, etc. throughout all filesystem-related calls
(i.e. stat, seek, etc.).
But if that is the case, then we should have gone with 64bit arguments in a single
register for our ILP32 definition on AArch64.
In other words: Why not keep ILP32 simple an ask users that need a 16TB+ offset
to use LP64? It seems much more consistent with the other choices takes so far.
—Phil.