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Subject: Re: [PATCH] POSIX-hostname up to 255 characters
Date: Fri, 26 May 2006 14:35:24 -0400
Message-ID: <Pine.LNX.4.61.0605261430370.8339@chaos.analogic.com>
In-Reply-To: <447748E4.4050908@redhat.com>
Thread-Topic: [PATCH] POSIX-hostname up to 255 characters
Thread-Index: AcaA8ycKx1PeWnm6QqGb91Efj+PNEg==
References: <20060525204534.4068e730.rdunlap@xenotime.net> <m1zmh5b129.fsf@ebiederm.dsl.xmission.com> <20060526144216.GZ13513@lug-owl.de> <Pine.LNX.4.58.0605261025230.9655@shark.he.net> <20060526180131.GA13513@lug-owl.de> <Pine.LNX.4.61.0605261409300.8002@chaos.analogic.com> <447748E4.4050908@redhat.com>
From: "linux-os \(Dick Johnson\)" <linux-os@analogic.com>
To: "Ulrich Drepper" <drepper@redhat.com>
Cc: "Jan-Benedict Glaw" <jbglaw@lug-owl.de>,
       "Randy.Dunlap" <rdunlap@xenotime.net>,
       "Eric W. Biederman" <ebiederm@xmission.com>,
       "lkml" <linux-kernel@vger.kernel.org>, "akpm" <akpm@osdl.org>,
       <serue@us.ibm.com>, <sam@vilain.net>, <clg@fr.ibm.com>, <dev@sw.ru>
Reply-To: "linux-os \(Dick Johnson\)" <linux-os@analogic.com>
Sender: linux-kernel-owner@vger.kernel.org
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On Fri, 26 May 2006, Ulrich Drepper wrote:

> linux-os (Dick Johnson) wrote:
>
>> MAXHOSTNAMELEN, defined by POSIX, is 64 bytes.
>
> Where do you think this is written?  The minimum maximum for the host
> name length in POSIX is 255.  This is the whole motivation of the patch.
> Linux currently cannot conform because this is one of the things the
> kernel gets wrong.
>
It is written (on so-called compatible machines like my Sun) as:

#define MAXHOSTNAMELEN _POSIX_HOST_NAME_MAX

Then in limits.h, I see:

#define _POSIX_HOST_NAME_MAX 64

Since somebody uses "POSIX" in the define, I assumed it had something
to do with POSIX. Further review using google shows even 256 as the
minimum-maximum so it's likely something that is now biting lots
of people.

>
>> You can't just
>> change it to 255. If you did, all servers in the universe, all
>> everything would have to be shutdown, recompiled, and rebooted
>> simultaneously. You can't have a name-server returning a 255-byte
>> string when a mail-server can only handle 64 bytes.
>
> The hostname is a machine-local value.  How the machine is represented
> to the outside world is governed by services like DNS.  DNS defines its
> own limits on the length of the name and each component.  So, if a host
> name (without domain) exceeds 64 bytes you need a different external
> name for the machine.  But this doesn't stop anybody from locally using
> a longer name.
>
> Can there be programs which have problems?  Certainly.  But
> gethostname() won't just overwrite memory.  It'll return an error and
> the programs with the wrong assumptions can be fix.
>
> --
> ?? Ulrich Drepper ?? Red Hat, Inc. ?? 444 Castro St ?? Mountain View, CA ??
>
>

Cheers,
Dick Johnson
Penguin : Linux version 2.6.16.4 on an i686 machine (5592.73 BogoMips).
New book: http://www.AbominableFirebug.com/
_


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