First Steps¶

First, create an instance of the Blivet class:

import blivet
b = blivet.Blivet()

Next, scan the system’s storage configuration and store it in the tree:

b.reset()

Now, you can do some simple things like listing the devices:

for device in b.devices:
    print(device)

To make changes to the configuration you’ll schedule actions, but Blivet provides some convenience methods to hide the details. Here’s an example of removing partition ‘/dev/sda3’:

sda3 = b.devicetree.get_device_by_name("sda3")
b.destroy_device(sda3)   # schedules actions to destroy format and device

At this point, the StorageDevice representing sda3 is no longer in the tree. That means you could allocate a new partition from the newly free space if you wanted to (via blivet, that is, since there is not actually any free space on the physical disk yet – you haven’t commited the changes). If you now ran the following line:

sda3 = b.devicetree.get_device_by_name("sda3")

sda3 would be None since that device has been removed from the tree.

When you are ready to commit your changes to disk, here’s how:

b.do_it()

That’s it. Now you have actually removed /dev/sda3 from the disk.

Here’s an alternative approach that uses the lower-level DeviceTree class directly:

import blivet
dt = blivet.devicetree.DeviceTree()
dt.populate()
sda3 = dt.get_device_by_name("sda3")
action1 = ActionDestroyFormat(sda3)
action2 = ActionDestroyDevice(sda3)
dt.actions.add(action1)
dt.actions.add(action2)
dt.actions.process()

Here’s the Blivet approach again for comparison:

import blivet
b = blivet.Blivet() # contains a DeviceTree instance
b.reset()   # calls DeviceTree.populate()
sda3 = b.devicetree.get_device_by_name("sda3")
b.destroy_device(sda3)   # schedules actions to destroy format and device
b.do_it()    # calls DeviceTree.actions.process()

Scheduling a Series of Actions¶

Start out as before:

import blivet
from blivet.size import Size
b = blivet.Blivet()
b.reset()
sda3 = b.devicetree.get_device_by_name("sda3")

Now we’re going to wipe the existing formatting from sda3:

b.destroy_format(sda3)

Now let’s assume sda3 is larger than 10GiB and resize it to that size:

b.resize_device(sda3, Size("10 GiB"))

And then let’s create a new ext4 filesystem there:

new_fmt = blivet.formats.get_format("ext4", device=sda3.path)
b.format_device(sda3, new_fmt)

If you want to commit the whole set of changes in one shot, it’s easy:

b.do_it()

Now you can mount the new filesystem at the directory “/mnt/test”:

sda3.format.setup(mountpoint="/mnt/test")

Once you’re finished, unmount it as follows:

sda3.format.teardown()

Disk Partitions¶

Disk partitions are a little bit tricky in that they require an extra step to actually allocate the partitions from free space on the disk(s). What that means is deciding exactly which sectors on which disk the new partition will occupy. Blivet offers some powerful means for deciding for you where to place the partitions, but it also allows you to specify an exact start and end sector on a specific disk if that’s how you want to do it. Here’s an example of letting Blivet handle the details of creating a partition of minimum size 10GiB on either sdb or sdc that is also growable to a maximum size of 20GiB:

sdb = b.devicetree.get_device_by_name("sdb")
sdc = b.devicetree.get_device_by_name("sdc")
new_part = b.new_partition(size=Size("10 GiB"), grow=True,
                           maxsize=Size("20 GiB"),
                           parents=[sdb, sdc])
b.create_device(new_part)
blivet.partitioning.do_partitioning(b)

Now you could see where it ended up:

print("partition %s of size %s on disk %s" % (new_part.name,
                                                 new_part.size,
                                                 new_part.disk.name))

From here, everything is the same as it was in the first examples. All that’s left is to execute the scheduled action:

b.do_it()    # or b.devicetree.process_actions()

Backing up, let’s see how it looks if you want to specify the start and end sectors. If you specify a start sector you have to also specify a single disk from which to allocate the partition:

new_part = b.new_partition(start=2048, end=204802048, parents=[sdb])

All the rest is the same as the previous partitioning example.

Explanation¶

In general, anything listed is public and anything not listed is not public. There are a couple of strange situations that deserve explanation:

• blivet.devicetree

  • DeviceTree

    • actions

      • add()
      • find()
      • prune()
      • remove()
      • sort()

    • cancel_disk_actions()

1. The class DeviceTree itself is listed, which means the constructor interface is considered to be stable.
2. DeviceTree has an ‘actions’ attribute that is an instance of class ActionList. ActionList’s constructor isn’t public, but the methods and attributes listed under the ‘actions’ attribute are.
3. DeviceTree has a ‘cancel_disk_actions’ method which is public.

• blivet.iscsi

  • iscsi

    • available()
    • create_interfaces()

1. The module blivet.iscsi contains a module-level ‘iscsi’ attribute, which is public.
2. The class iSCSI is not public. You shouldn’t create instances of it. Instead, you should use the existing instance at blivet.iscsi.iscsi.
3. The ‘available’ and ‘create_interfaces’ methods of the iSCSI class are public. The above example is incomplete, but if it were complete it would mean that the only public members of the iSCSI class are the ‘available’ and ‘create_interfaces’ methods.