Johan Kiviniemi’s series of tubes

Upstart and mounting partitions, part 2

2007-03-19

There has been a nice discussion about my previous post on the Upstart mailing list. Here’s an updated version with the ideas from the list applied.

The examples still do not check whether the filesystems should be checked automatically, and lack error checking. That will be trivial to add, but for now, I’ll focus on simplicity.

/etc/event.d/fsck

start on block-device-added

instance

script
    locks="$(sysblock --short --physdev "$DEVNAME")"
    # DEVNAME=/dev/mapper/vg-root → locks="sda sdb" (RAID-1)
    # DEVNAME=/dev/sda1           → locks="sda"

    locking $locks -- fsck -y "$DEVNAME"

    initctl variable append checked-filesystems "$DEVNAME"

    initctl emit filesystem-checked "$DEVNAME" -eDEVNAME
end script

/etc/event.d/mount

start on filesystem-checked
start on filesystem-mounted

instance

script
    initctl variable list checked-filesystems | while read devname; do
        mountpoint="$(getmntent -fD "$devname")"

        if getmntent --prereqs-satisfied -d "$mountpoint"; then
            mount "$mountpoint"

            initctl variable remove checked-filesystems "$devname"

            initctl emit filesystem-mounted "$mountpoint" \\
                -eDEVNAME="$devname" -eMOUNTPOINT="$mountpoint"
        fi
    done
end script

The commands

• initctl variable has the following subcommands:

  • clear NAME: Removes all entries from NAME. The underlying implementation frees NAME from memory if it becomes empty, and any operations transparently allocate a new list on demand.
  • set NAME VALUE [...]: Sets NAME to [VALUE], or [VALUE0, VALUE1, ...] in case of multiple VALUE parameters, overwriting any existing values. Any duplicate entries are ignored.
  • append NAME VALUE [...]: Appends each VALUE to the list NAME. If any of them already exist in NAME, they are ignored.
  • remove NAME VALUE [...]: Removes each VALUE from the list NAME. If any of them do not exist in NAME, they are ignored.
  • list NAME: Prints each entry to stdout on separate lines.

• The getmntent command will grow the following functionality:

  • --prereqs: Implies -f (parse /etc/fstab). Prints each fstab entry that is a prerequisite of the mountpoint in question, e.g. / and /var need to be mounted before /var/tmp is mounted, if all of them exist in fstab.
  • --prereqs-satisfied: Computes the list of prerequisite mounts from /etc/fstab and exits with the return value of 0 if all of them exist in /etc/mtab (that is, all of them are already mounted), or 1 if some of them are still not mounted.

• locking [LOCKNAME ...] -- CMDLINE

  locking(1) opens and exclusively locks sprintf ("/var/run/locking/%s.%s", sanitize (lockname), sha1sum (lockname)) for each LOCKNAME and runs the command.

• sysblock [--short] [--dev] [--parent|--slaves|--holders|--physdev] [DEVICE ...]

  sysblock(1) maps /dev nodes to /sys/block nodes and vice versa. All /dev paths listed on the command line are converted to their /sys/block equivalents before processing. When called with the --dev parameter, the resulting output list of /sys/block paths is converted to the /dev equivalents.

  With the --parent parameter, it converts /sys/block/foo/bar to /sys/block/foo, and /sys/block/baz to nothing.

  With the --slaves or the --holders parameter, it lists the devices linked from /sys/block/device/slaves or /sys/block/device/holders respectively.

  With the --physdev parameter, it follows each device’s parents or slaves, until it reaches the end of the tree. The final devices it ended up at are listed.

  Usage examples:

  sysblock /dev/sda1                             → /sys/block/sda/sda1
  sysblock --dev /sys/block/sda/sda1             → /dev/sda1
  sysblock --dev sda/sda1                        → /dev/sda1
  
  

  (/sys/block prefix is assumed)

  sysblock --short /dev/sda1                     → sda/sda1
  sysblock --short --dev /sys/block/sda/sda1     → sda1
  sysblock --short --dev sda/sda1                → sda1
  
  sysblock --short /dev/mapper/vg-root           → dm-0
  sysblock --short --slaves /dev/mapper/vg-root  → md0
  sysblock --short --slaves md0                  → sda/sda1 sdb/sdb1
  sysblock --short --parent sda/sda1 sdb/sdb1    → sda sdb
  
  sysblock --short --physdev /dev/mapper/vg-root → sda sdb
  
  sysblock --dev --physdev /dev/mapper/vg-root   → /dev/sda /dev/sdb