From: sdw@lig.net (Stephen D. Williams)
Date: Thu, 2 Nov 1995 10:32:40 +0800
To: Mike_Spreitzer.PARC@xerox.com
Subject: Re: /dev/random for FreeBSD [was: Re: /dev/random for Linux]
In-Reply-To: <95Oct31.094528pst."14855(1)"@alpha.xerox.com>
Message-ID: <m0tAoYD-0009yxC@sdwsys>
MIME-Version: 1.0
Content-Type: text/plain


Besides non-blocking, it's very useful sometimes to support SIGIO/SIGURG for
as many devices as possible.

I know only too well that Sybase CT_lib uses this for Async mode.
(I just tracked down what appears to be an HPUX process group bug preventing
 the signals from being delivered...)

In any case, using SIGIO is a whole parallel method to using a select loop,
and although it seemed like a hack when I found out they were using it, it
has some elegance since they chain to other possible signal handlers in
case other io descriptors are ready.

> Blocking vs. non-blocking is a standard issue in design of U*X devices.
> Standard solution: make it block by default, and accept an IOCTL to put it in
> non-blocking mode.  There's even a POSIX way to do this:
> 
> 	flags_or_err = fcntl(fd, F_GETFL, 0);
> 	{check for error}
> 	res = fcntl(fd, F_SETFL, flags_or_err | O_NONBLOCK);
> 	{check for error}

sdw
-- 
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