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Re: OpenVMS getdtablesize.c

From: Bruno Haible
Subject: Re: OpenVMS getdtablesize.c
Date: Wed, 28 Jun 2017 22:56:13 +0200
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John E. Malmberg wrote:
> OpenVMS has the function.  Configure detects it exists, but the test for 
> it working is failing.
> ...
> The OpenVMS getdtablesize() is returning the maximum number of open 
> files that a process can have.
> It is not returning the highest file descriptor + 1 that can be used in 
> the system.  That number is 65535 for OpenVMS Alpha and Integrity.
> That is why it is failing the configure test.

There are two possibilities:
  (a) change the configure test so that is duplicates
      fd 0 to 1, 2, 3, ..., getdtablesize() and see if that fails.
  (b) special-case OpenVMS.

I'm not in favour of (a) because it might allocate so many file descriptors
that the kernel gets problems.

So (b). Just add a few lines

  case "$host_os" in
    vms*) ...

at the appropriate place. Can you propose such a patch?

> If I have a replacement getdtablesize() return 65535, that could cause 
> programs to assume that they could actually open that many descriptors.

This is only a theoretical risk. I know of no programs that are that

> And if an OpenVMS getrlimit() is provided, what value should it provide 

Please try to approximate the wording of POSIX [1] as closely as possible.


[1] http://pubs.opengroup.org/onlinepubs/9699919799/functions/getrlimit.html

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