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Re: d_off field in struct dirent and 32-on-64 emulation
- From: Adhemerval Zanella <adhemerval dot zanella at linaro dot org>
- To: Florian Weimer <fw at deneb dot enyo dot de>
- Cc: linux-fsdevel at vger dot kernel dot org, linux-api at vger dot kernel dot org, linux-ext4 at vger dot kernel dot org, linux-kernel at vger dot kernel dot org, v9fs-developer at lists dot sourceforge dot net, libc-alpha at sourceware dot org, qemu-devel at nongnu dot org, ericvh at gmail dot com, lucho at ionkov dot net, hpa at zytor dot com, arnd at arndb dot de
- Date: Fri, 28 Dec 2018 10:21:03 -0200
- Subject: Re: d_off field in struct dirent and 32-on-64 emulation
- References: <87bm56vqg4.fsf@mid.deneb.enyo.de> <957967d7-5717-8ada-fb30-dfdf19898b6b@linaro.org> <87pntmu9iw.fsf@mid.deneb.enyo.de> <ae0530c9-5c46-5560-9734-1eacaf173b8d@linaro.org> <87k1jtvp8u.fsf@mid.deneb.enyo.de> <87ftuhvp08.fsf@mid.deneb.enyo.de>
On 28/12/2018 10:01, Florian Weimer wrote:
> * Florian Weimer:
>
>> * Adhemerval Zanella:
>>
>>> On 27/12/2018 16:09, Florian Weimer wrote:
>>>> * Adhemerval Zanella:
>>>>
>>>>> Also for glibc standpoint, although reverting it back to use getdents
>>>>> syscall for non-LFS mode might fix this issue for architectures that
>>>>> provides non-LFS getdents syscall it won't be a fix for architectures
>>>>> that still provides off_t different than off64_t *and* only provides
>>>>> getdents64 syscall.
>>>>>
>>>>> Currently we only have nios2 and csky (unfortunately). But since generic
>>>>> definition for off_t and off64_t still assumes non-LFS support, all new
>>>>> 32-bits ports potentially might carry the issue.
>>>>
>>>> For csky, we could still change the type of the non-standard d_off
>>>> field to long long int. This way, only telldir would have to fail
>>>> when truncation is necessary, as mentioned below:
>>>
>>> I think it makes no sense to continue making non-LFS as default for
>>> newer 32 bits ports, the support will be emulated with LFS syscalls.
>>
>> Sorry, I don't see how this matters. seekdir and telldir are NOT
>> affected by LFS.
>
> Ah, right. If struct dirent is 64-bit only, then the d_off member
> will be 64 bits as well. But it is unclear whether you can use that
> with lseek (probably yes, in its 64-bit variant), and it's unlikely
> it's going to work with seekdir because of the POSIX-required long int
> type.
>
I was referring to all other API that uses off_t as well (pread for
instance), where new ports will have non-LFS variants that will call
only LFS variants.