Re: BUG #15964: vacuumdb.c:187:10: error: use of undeclared identifier 'FD_SETSIZE'

From: Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Michael Paquier <michael(at)paquier(dot)xyz>, Andres Freund <andres(at)anarazel(dot)de>, Dilip Kumar <dilipbalaut(at)gmail(dot)com>, jungleboogie0(at)gmail(dot)com, pgsql-bugs(at)lists(dot)postgresql(dot)org
Subject: Re: BUG #15964: vacuumdb.c:187:10: error: use of undeclared identifier 'FD_SETSIZE'
Date: 2019-08-21 14:34:49
Message-ID: 20190821143449.GA27852@alvherre.pgsql
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On 2019-Aug-21, Tom Lane wrote:

> Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> writes:
> > I guess the other possibility is that there exists an operating system
> > that returns file descriptors higher than its FD_SETSIZE, when some fds
> > below FD_SETSIZE are still available. Doesn't seem realistic.
>
> I think POSIX requires open() to select the lowest unused FD. Otherwise
> tricks like closing and reopening stdout wouldn't work reliably.

Ah, yes, that's right -- my system's open(3p) manpage says:

The open() function shall return a file descriptor for the named file
that is the lowest file descriptor not currently open for that process.

--
Álvaro Herrera https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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