Re: [PATCH 03/10] linux: Add __readdir_unlocked

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

On 21/04/2020 07:41, Florian Weimer wrote:
> * Adhemerval Zanella via Libc-alpha:
> 
>> And use it on readdir_r implementation.
> 
> I think __readdir_unlocked will not really be async-signal-safe if we
> have to call malloc during readdir, to allocate the long-to-off64_t
> translation table for the real fix for bug 23960 (when the kernel does
> not provide 32-bit off64_t values).
> 
> That's why I think this change does not go in the right direction, sorry.
> 

I am not following, the whole set explicit avoid malloc by using a reserved
space in the allocated but on opendir.  Even on mips64, which requires
a special getdents64 implementation, avoid memory allocation.

And it is for both non-LFS and LFS interfaces.  The only issue for 
async-signal-safeness is on telldir for non-LFS mode which might require
to extend the dynamic array internal buffer if the entry could not be
added in the internal pre-allocated buffer (and this could be mitigated
if we added a mmap variant of dynamic array). 

But these interfaces are also not marked as async-signal-safe in any case 
by POSIX and if the idea is indeed move in this direction we should first
move opendir buffer allocation to use mmap instead.  I am not sure bounding
glibc implementation to this requirement is really a gain, no other libc
implementation I am aware of also provide async-safe-signal.

This change also has the effect of consolidate readdir implementation
and remove code logic duplication.