Date: Wed, 26 Jul 2000 11:50:03 -0400 (EDT) From: Robert Watson <rwatson@FreeBSD.org> To: freebsd-hackers@FreeBSD.org Cc: ogud@tislabs.com, marka@nominum.com, markm@FreeBSD.org Subject: kern/19863: Non-blocking IO not supported on /dev/random Message-ID: <Pine.NEB.3.96L.1000726114114.75784A-100000@fledge.watson.org>
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Hi there,
This was brought to my attention by a co-worker, and is a legitimate
complaint about our device handling for {/dev/null, /dev/random,
/dev/urandom, /dev/zero, ...}. Apparently it is not possible to set the
device to support non-blocking file I/O, which seems silly as the
semantics of the device should permit it. In order for these devices to
be used properly from threaded programs based on a select() loop,
non-blocking mode is required.
Unfortunately, we didn't give the best answer to the initial bug report:
Synopsis: Non-blocking IO not supported on /dev/random
Responsible-Changed-From-To: freebsd-bugs->markm
Responsible-Changed-By: sheldonh
Responsible-Changed-When: Wed Jul 12 01:33:02 PDT 2000
Responsible-Changed-Why:
Mark Murray has recently re-implemented the random device in
the development branch of FreeBSD. This makes him the closest
thing we have to a maintainer, although that may just mean
you'll have to wait for the new devices to be merged back onto the
stable branch.
By the way, are you sure /dev/urandom doesn't do what you want?
http://www.freebsd.org/cgi/query-pr.cgi?pr=19863
/dev/urandom also does not allow the setting of non-blocking mode.
This is probably something that needs to be fixed; it's a pity we didn't
catch this before 4.1-RELEASE. I looked through the code some, and noted
that /dev/{useful_virtual_stuff} don't implement ioctl(), specifically,
support for async I/O, which apparently is required to enable non-blocking
I/O (fo_ioctl()).
Note that I believe it is insufficient for us to simply provide
non-blocking semantics for the device, we actually have to support the
flag also for application compatibility. Apparently /dev/random *does*
behave correctly on other platforms (Linux, NetBSD, ...) Given that
/dev/random is frequently used by security programs, providing correct and
consistent semantics is important.
This has been demonstrated both in the old /dev/random in 4.x, as well as
the revised 5.x devices.
Robert N M Watson
robert@fledge.watson.org http://www.watson.org/~robert/
PGP key fingerprint: AF B5 5F FF A6 4A 79 37 ED 5F 55 E9 58 04 6A B1
TIS Labs at Network Associates, Safeport Network Services
---------- Forwarded message ----------
Date: Tue, 11 Jul 2000 23:41:08 -0700 (PDT)
From: marka@nominum.com
To: freebsd-gnats-submit@FreeBSD.org
Subject: kern/19863: Non-blocking IO not supported on /dev/random
>Number: 19863
>Category: kern
>Synopsis: Non-blocking IO not supported on /dev/random
>Confidential: no
>Severity: non-critical
>Priority: medium
>Responsible: freebsd-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Tue Jul 11 23:50:03 PDT 2000
>Closed-Date:
>Last-Modified:
>Originator: Mark Andrews
>Release: 4.0-stable
>Organization:
Nominum
>Environment:
FreeBSD drugs.dv.isc.org 4.0-STABLE FreeBSD 4.0-STABLE #1: Sat Jul 1 00:10:47 EST 2000 root@drugs.dv.isc.org:/usr/src/sys/compile/DRUGS i386
>Description:
It is not possible to set /dev/random into non-blocking mode using
fcntl. This make it impossible to use /dev/random in a application
that requires IO not to block.
>How-To-Repeat:
#include <fcntl.h>
#include <stdio.h>
int
main(int argc, char **argv) {
int fd;
int flags;
if ((fd = open("/dev/random", O_RDONLY, 0)) == -1) {
perror("open");
exit(1);
}
if ((flags = fcntl(fd, F_GETFL, 0)) == -1) {
perror("fcntl: F_GETFL");
exit(1);
}
flags |= O_NONBLOCK;
if (fcntl(fd, F_SETFL, flags) == -1) {
perror("fcntl: F_SETFL");
exit(1);
}
close(fd);
exit(0);
}
>Fix:
>Release-Note:
>Audit-Trail:
>Unformatted:
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