Re: d_off field in struct dirent and 32-on-64 emulation

From: Florian Weimer
Date: Fri Dec 28 2018 - 07:01:49 EST

* 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