debian/spl.postinst

   1 #!/bin/sh -e
   2
   3 # The hostname and hostid of the last system to access a ZFS pool are stored in
   4 # the ZFS pool itself.  A pool is foreign if, during `zfs import`, the current
   5 # hostname and hostid are different than the stored values thereof.
   6 #
   7 # The hostname and hostid on Solaris are intrinsic, but they are not on Linux,
   8 # so the spl kernel module invokes /bin/hostname and /usr/bin/hostid from the
   9 # userland in its initialization routine.
  10 #
  11 # However, these two indentifiers are usually undefined in the Linux initramfs
  12 # environment, so the /etc/hostname and /etc/hostid files must be added to the
  13 # initrd.  Things like a DHCP lease change can affect the hostid too.
  14 #
  15 # ZFS requires stable values for hostname and hostid, but basic Linux systems
  16 # do not.  The hostid is therefore stabilized by creating the /etc/hostid file
  17 # in the regular environment if it does not already exist.  An undefined
  18 # hostname is usuallly stable.
  19 #
  20 # Neither /etc/hostname nor /etc/hostid are controlled configuration files in
  21 # Debian distributions, but the spl package nevertheless installs a dummy
  22 # /etc/hostid file that contains the HW_INVALID_HOSTID sentinal value so that
  23 # the package manager will track it.
  24
  25 # This result is always an eight-character hexadecimal number sans the 0x
  26 # prefix.  Remember that /usr/bin/hostid generates a value if the /etc/hostid
  27 # file doesn't exist or is malformed.
  28 HOSTID=$(hostid)
  29
  30 if [ -f /etc/hostid -a "0x$HOSTID" != "0xffffffff" ]
  31 then
  32         # This system already has a stable hostid.
  33         exit 0
  34 fi
  35
  36 # Truncate the dummy file and generate the actual system hostid.
  37 : >/etc/hostid
  38 HOSTID=$(hostid)
  39
  40 # @TODO: Check whether this method is appropriate for gethostid(2) on big
  41 # endian systems.  The /etc/hostname file on i386 and amd64 systems must be
  42 # a little endian integer of exacly four bytes.  Regardless, a consistent
  43 # hostid is more important than a correct byte order here.
  44
  45 # Conveniences like a ${HOSTID:$ii:2} substring range or a `sed` one-liner
  46 # are prohibited here because this file must be dash-compatible by policy.
  47 AA=$(echo $HOSTID | cut -b 1,2)
  48 BB=$(echo $HOSTID | cut -b 3,4)
  49 CC=$(echo $HOSTID | cut -b 5,6)
  50 DD=$(echo $HOSTID | cut -b 7,8)
  51
  52 # Invoke the external printf because the dash builtin lacks the byte format.
  53 "$(which printf)" "\x$DD\x$CC\x$BB\x$AA" >"/etc/hostid"
  54
  55 # @ASSERT: [ "$HOSTID" = "$(hostid)" ]