Re: [PATCH] change thread-unsafe readdir to thread-safe readdir_r calls

[Steven Dake <sdake-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

On 07/07/2010 02:49 PM, Jason Gunthorpe wrote:
> On Wed, Jul 07, 2010 at 02:24:45PM -0700, Steven Dake wrote:
>
>> Not sure how to map a readdir to readdir_r on a thread unsafe system...
>> perhaps with thread keys.  In any regard, seems pointless, readdir_r is
>> there and what POSIX specifies for this purpose.
>
> Override opendir and allocate the buffer then and return a pointer to it
> through a custom 'DIR *'.
>
>>> FWIW, I've always considered readdir_r to be broken, you pass in a
>>> buffer without passing in a size and hope everything works out. Your
>>
>> I also have objections to some POSIX standard APIs - however, using
>> non-reentrant POSIX apis when reentrant POSIX APIs are available seems
>> counterproductive.
>
> Well, if the non-reentrant ones are badly designed I'm not sure it is
> a good trade.. Ie Solaris's man pages say:
>
>   It is safe to use readdir() in a threaded application, so long as only
>   one thread reads from the directory stream at any given time. The
>   readdir() function is generally preferred over the readdir_r()
>   function.
>
> Also see
>
> http://lists.grok.org.uk/pipermail/full-disclosure/2005-November/038295.html
>
> The horribleness of readdir_r is well documented, and is partly why
> libc's advocate thread safe readdir() desipte the existence of
> readdir_r.
>
>>> proposed patch to libibverbs is also not-portable because it uses
>>> NAME_MAX, not pathconf.. Sigh POSIX.
>
>> On bsd/solaris/darwin/linux, NAME_MAX is defined.  Not sure which other
>> POSIX systems one would care about..
>
> If all you care able is bsd/solaris/darwin/linux then this is a
> non-problem, AFAIK they have sane libc's :) Ie I just checked and
> openbsd libc has been using a dynamic buffer allocated at opendir
> since 1996.
>
> If you care about theortical portability then you have to worry about
> NAME_MAX too..
>

Thanks I'll look into NAME_MAX for my server.

Regards
-steve
> Jason

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