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Date: Sun, 03 Nov 2013 18:16:09 +0100
From: "Thomas Schmitt" <scdbackup@gmx.net>
To: grub-devel@gnu.org
Subject: Re: How important is the MBR partition offset of grub-mkrescue ?
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Hi,

i believe to have found the udev rules in Debian 6 which
govern the population of /dev/disk/by-label.

File
  /lib/udev/rules.d/60-persistent-storage.rules
has
  # probe filesystem metadata of disks
  KERNEL!="sr*", IMPORT{program}="/sbin/blkid -o udev -p $tempnode"
  ...
  ENV{ID_FS_LABEL_ENC}=="?*",     ENV{ID_FS_USAGE}=="filesystem|other", \
          SYMLINK+="disk/by-label/$env{ID_FS_LABEL_ENC}"

I understand that if blkid sets variable ID_FS_LABEL_ENC to
a non-empty value, then this will become the link name in ./by-label.
The link target is the device that is being examined by the rule.

>From a USB stick with partition start LBA 1, i get:

  $ /sbin/blkid -o udev -p /dev/sdb 
  ID_PART_TABLE_TYPE=dos
  ID_FS_LABEL=epidemic-4.1-b1-1-ts-amd64
  ID_FS_LABEL_ENC=epidemic-4.1-b1-1-ts-amd64
  ID_FS_TYPE=iso9660
  ID_FS_USAGE=filesystem
  $ /sbin/blkid -o udev -p /dev/sdb1
  $

So why the hell does /dev/sdb1 become link target ?
Its ID_FS_LABEL_ENC must be empty.

Any idea how to get a verbous log of these decisions ?


Have a nice day :)

Thomas