linux-kernel - Re: what's the purpose of MAXHOSTNAMELEN?

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Date:	Tue, 29 Dec 2009 14:40:05 -0500
From:	Jeff Garzik <jeff@...zik.org>
To:	"Robert P. J. Day" <rpjday@...shcourse.ca>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: what's the purpose of MAXHOSTNAMELEN?

On 12/29/2009 02:19 PM, Robert P. J. Day wrote:
>
>    in prepping for coalescing a lot of param.h files, i'm curious about
> the purpose of this macro:
>
> $ grep -rw MAXHOSTNAMELEN *
> arch/s390/include/asm/param.h:#define MAXHOSTNAMELEN	64	/* max length of hostname */
> arch/sparc/include/asm/param.h:#define MAXHOSTNAMELEN	64	/* max length of hostname */
> arch/alpha/include/asm/param.h:#define MAXHOSTNAMELEN	64	/* max length of hostname */
> arch/mn10300/include/asm/param.h:#define MAXHOSTNAMELEN	64	/* max length of hostname */
> arch/arm/include/asm/param.h:#define MAXHOSTNAMELEN  64
> arch/m32r/include/asm/param.h:#define MAXHOSTNAMELEN	64	/* max length of hostname */
> arch/mips/include/asm/param.h:#define MAXHOSTNAMELEN	64	/* max length of hostname */
> arch/m68k/include/asm/param.h:#define MAXHOSTNAMELEN	64	/* max length of hostname */
> arch/xtensa/include/asm/param.h:#define MAXHOSTNAMELEN	64	/* max length of hostname */
> arch/ia64/include/asm/param.h:#define MAXHOSTNAMELEN	64	/* max length of hostname */
> arch/h8300/include/asm/param.h:#define MAXHOSTNAMELEN	64	/* max length of hostname */
> arch/avr32/include/asm/param.h:#define MAXHOSTNAMELEN	64
> arch/cris/include/asm/param.h:#define MAXHOSTNAMELEN	64	/* max length of hostname */
> arch/um/include/asm/param.h:#define MAXHOSTNAMELEN  64      /* max length of hostname */
> arch/powerpc/include/asm/param.h:#define MAXHOSTNAMELEN	64	/* max length of hostname */
> arch/parisc/include/asm/param.h:#define MAXHOSTNAMELEN	64	/* max length of hostname */
> arch/frv/include/asm/param.h:#define MAXHOSTNAMELEN		64	/* max length of hostname */
> include/asm-generic/param.h:#define MAXHOSTNAMELEN	64	/* max length of hostname */
> include/net/sctp/structs.h:#include<asm/param.h>		/* We get MAXHOSTNAMELEN.     */
> $
>
>    so lots of people define it but no one uses it.  it *is* exported to
> user space in /usr/include/asm/param.h, but i still have no idea what
> it's for in user space.  obsolete?

According to RFC 1034, "Each node has a label, which is zero to 63 
octets in length"

What is it used for in userspace, and why is it export from the kernel? 
  Good question...

	Jeff



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