How to edit partition labels?

[Robert P. J. Day]

On Thu, 5 Aug 2004, Alexander Dalloz wrote:

> Am Do, den 05.08.2004 schrieb Robert P. J. Day um 20:23:
>
>>>> The Linux kernel requires BSD disk label support compiled in
>>>> (CONFIG_BSD_DISKLABEL=y) to use the labels with fstab and how it is used
>>>> as kernel command line in the grub.conf on Fedora (Redhat) systems.
>>
>> really?  i've used e2label many times for labelling filesystems, and
>> i've never built a kernel with BSD labelling.  are you sure about
>> this?  (time to go RTFS, i guess.)
>>
>> rday
>
> Hm, I am becoming a bit uncertain when you say that the labels in fstab
> work for you on a custom kernel without BSD disklabel support and
> because I can't find the source of my "knowledge". If it would be not a
> big deal and not last that long, I would compile a kernel without
> support for BSD disklabels and try it out.

i don't have the resources to do that at this second, but i just took 
a look at the Kconfig file in fs/partitions, and here's the entry for 
that feature:

config BSD_DISKLABEL
 	bool "BSD disklabel (FreeBSD partition tables) support"
 	depends on PARTITION_ADVANCED && MSDOS_PARTITION
 	help
 	  FreeBSD uses its own hard disk partition scheme on your PC. It
 	  requires only one entry in the primary partition table of your disk
 	  and manages it similarly to DOS extended partitions, putting in its
 	  first sector a new partition table in BSD disklabel format. Saying Y
 	  here allows you to read these disklabels and further mount FreeBSD
 	  partitions from within Linux if you have also said Y to "UFS
 	  file system support", above. If you don't know what all this is
 	  about, say N.

and i know i've built lots of kernels without this feature, and done 
lots of e2labels, and never had a problem.  so if i've missed getting 
burned by this all this time, i've been indescribably lucky.

rday

p.s.  just making this as difficult as possible, rather than actually 
test it, i took a look at the include file include/linux/ext2_fs.h in 
the kernel source tree, where we find:

struct ext2_super_block {
 	__u32	s_inodes_count;		/* Inodes count */
 	__u32	s_blocks_count;		/* Blocks count */
 	...
 	char	s_volume_name[16]; 	/* volume name */   <--- hmmm
 	...

and the man page for e2label:

... Ext2 filesystem labels can be at most 16 characters long;  if 
new-label is longer than 16 characters, e2label will truncate it and 
print a warning message....

16 character limits in both places.  coincidence?  (yes, i'm clearly 
bored today.)