Re: [PATCH 2/3] getdtablesize: Extend RLIMIT_NOFILE fallback case to Android

[enh]

https://android-review.googlesource.com/132781 fixes the sysconf implementation.

On Tue, Feb 17, 2015 at 9:47 AM, Kevin Cernekee <address@hidden> wrote:
> On Mon, Feb 16, 2015 at 9:46 PM, Paul Eggert <address@hidden> wrote:
>> The other patches (after your revisions) look good and I installed them, but
>> this one didn't look right.  That part of the code really is intended to be
>> used only on Cygwin and it's not portable to other platforms (e.g., it
>> mishandles RLIM_SAVED_MAX).  I suppose we could get it to work on Android
>> too but let's not bother.  Instead, let's not use Android's getdtablesize
>> since it's obsolescent.
>>
>> I installed the attached patch instead, which I hope solves the problem in a
>> different way.  Please let me know whether it works on Android.
>
> On Android, sysconf (_SC_OPEN_MAX) always returns the constant
> OPEN_MAX (256).  So if `ulimit -n` is not exactly 256,
> test-{dup2,fcntl,getdtablesize} all fail because they think the OS
> should have stopped them from using file descriptor 256.
>
> Android behavior: (android-21, arm 32-bit)
>
> # /shared/tmp/fdtest
> rlimit: 1024
> sysconf: 256
> getdtablesize: 1024
>
> Ubuntu/glibc behavior:
>
> $ /tmp/fdtest
> rlimit: 32768
> sysconf: 32768
> getdtablesize: 32768
>
>
> Test program:
>
> #include <unistd.h>
> #include <stdio.h>
> #include <sys/time.h>
> #include <sys/resource.h>
>
> int main(int argc, char **argv)
> {
>     struct rlimit lim;
>
>     if (getrlimit (RLIMIT_NOFILE, &lim) == 0)
>         printf("rlimit: %d\n", (int)lim.rlim_cur);
>     printf("sysconf: %ld\n", sysconf (_SC_OPEN_MAX));
>     printf("getdtablesize: %d\n", getdtablesize());
>     return 0;
> }
>
>
> FWIW, the deprecated Bionic getdtablesize() function is implemented as:
>
> // This was removed from POSIX 2004.
> extern "C" int getdtablesize() {
>   struct rlimit r;
>
>   if (getrlimit(RLIMIT_NOFILE, &r) < 0) {
>     return sysconf(_SC_OPEN_MAX);
>   }
>
>   return r.rlim_cur;
> }



-- 
Elliott Hughes - http://who/enh - http://jessies.org/~enh/
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