Re: [PATCH] POSIX-hostname up to 255 characters

["linux-os \(Dick Johnson\)" <linux-os@analogic.com>]

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.
>
> --
> ÿÿ Ulrich Drepper ÿÿ Red Hat, Inc. ÿÿ 444 Castro St ÿÿ Mountain View, CA ÿÿ
>
>

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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