moby--moby/experimental/plugins_graphdriver.md

Experimental: Docker graph driver plugins

Docker graph driver plugins enable admins to use an external/out-of-process graph driver for use with Docker engine. This is an alternative to using the built-in storage drivers, such as aufs/overlay/devicemapper/btrfs.

A graph driver plugin is used for image and container fs storage, as such the plugin must be started and available for connections prior to Docker Engine being started.

Write a graph driver plugin

See the plugin documentation for detailed information on the underlying plugin protocol.

Graph Driver plugin protocol

If a plugin registers itself as a GraphDriver when activated, then it is expected to provide the rootfs for containers as well as image layer storage.

/GraphDriver.Init

Request:

{
  "Home": "/graph/home/path",
  "Opts": []
}

Initialize the graph driver plugin with a home directory and array of options. Plugins are not required to accept these options as the Docker Engine does not require that the plugin use this path or options, they are only being passed through from the user.

Response:

{
  "Err": ""
}

Respond with a non-empty string error if an error occurred.

/GraphDriver.Create

Request:

{
  "ID": "46fe8644f2572fd1e505364f7581e0c9dbc7f14640bd1fb6ce97714fb6fc5187",
  "Parent": "2cd9c322cb78a55e8212aa3ea8425a4180236d7106938ec921d0935a4b8ca142"
  "MountLabel": ""
}

Create a new, empty, read-only filesystem layer with the specified ID, Parent and MountLabel. Parent may be an empty string, which would indicate that there is no parent layer.

Response:

{
  "Err": ""
}

Respond with a non-empty string error if an error occurred.

/GraphDriver.CreateReadWrite

Request:

{
  "ID": "46fe8644f2572fd1e505364f7581e0c9dbc7f14640bd1fb6ce97714fb6fc5187",
  "Parent": "2cd9c322cb78a55e8212aa3ea8425a4180236d7106938ec921d0935a4b8ca142"
  "MountLabel": ""
}

Similar to /GraphDriver.Create but creates a read-write filesystem layer.

/GraphDriver.Remove

Request:

{
  "ID": "46fe8644f2572fd1e505364f7581e0c9dbc7f14640bd1fb6ce97714fb6fc5187"
}

Remove the filesystem layer with this given ID.

Response:

{
  "Err": ""
}

Respond with a non-empty string error if an error occurred.

/GraphDriver.Get

Request:

{
  "ID": "46fe8644f2572fd1e505364f7581e0c9dbc7f14640bd1fb6ce97714fb6fc5187"
  "MountLabel": ""
}

Get the mountpoint for the layered filesystem referred to by the given ID.

Response:

{
  "Dir": "/var/mygraph/46fe8644f2572fd1e505364f7581e0c9dbc7f14640bd1fb6ce97714fb6fc5187",
  "Err": ""
}

Respond with the absolute path to the mounted layered filesystem. Respond with a non-empty string error if an error occurred.

/GraphDriver.Put

Request:

{
  "ID": "46fe8644f2572fd1e505364f7581e0c9dbc7f14640bd1fb6ce97714fb6fc5187"
}

Release the system resources for the specified ID, such as unmounting the filesystem layer.

Response:

{
  "Err": ""
}

Respond with a non-empty string error if an error occurred.

/GraphDriver.Exists

Request:

{
  "ID": "46fe8644f2572fd1e505364f7581e0c9dbc7f14640bd1fb6ce97714fb6fc5187"
}

Determine if a filesystem layer with the specified ID exists.

Response:

{
  "Exists": true
}

Respond with a boolean for whether or not the filesystem layer with the specified ID exists.

/GraphDriver.Status

Request:

{}

Get low-level diagnostic information about the graph driver.

Response:

{
  "Status": [[]]
}

Respond with a 2-D array with key/value pairs for the underlying status information.

/GraphDriver.GetMetadata

Request:

{
  "ID": "46fe8644f2572fd1e505364f7581e0c9dbc7f14640bd1fb6ce97714fb6fc5187"
}

Get low-level diagnostic information about the layered filesystem with the with the specified ID

Response:

{
  "Metadata": {},
  "Err": ""
}

Respond with a set of key/value pairs containing the low-level diagnostic information about the layered filesystem. Respond with a non-empty string error if an error occurred.

/GraphDriver.Cleanup

Request:

{}

Perform necessary tasks to release resources help by the plugin, for example unmounting all the layered file systems.

Response:

{
  "Err": ""
}

Respond with a non-empty string error if an error occurred.

/GraphDriver.Diff

Request:

{
  "ID": "46fe8644f2572fd1e505364f7581e0c9dbc7f14640bd1fb6ce97714fb6fc5187",
  "Parent": "2cd9c322cb78a55e8212aa3ea8425a4180236d7106938ec921d0935a4b8ca142"
}

Get an archive of the changes between the filesystem layers specified by the ID and Parent. Parent may be an empty string, in which case there is no parent.

Response:

{{ TAR STREAM }}

/GraphDriver.Changes

Request:

{
  "ID": "46fe8644f2572fd1e505364f7581e0c9dbc7f14640bd1fb6ce97714fb6fc5187",
  "Parent": "2cd9c322cb78a55e8212aa3ea8425a4180236d7106938ec921d0935a4b8ca142"
}

Get a list of changes between the filesystem layers specified by the ID and Parent. Parent may be an empty string, in which case there is no parent.

Response:

{
  "Changes": [{}],
  "Err": ""
}

Responds with a list of changes. The structure of a change is:

  "Path": "/some/path",
  "Kind": 0,

Where the Path is the filesystem path within the layered filesystem that is changed and Kind is an integer specifying the type of change that occurred:

• 0 - Modified
• 1 - Added
• 2 - Deleted

Respond with a non-empty string error if an error occurred.

/GraphDriver.ApplyDiff

Request:

{{ TAR STREAM }}

Extract the changeset from the given diff into the layer with the specified ID and Parent

Query Parameters:

• id (required)- the ID of the new filesystem layer to extract the diff to
• parent (required)- the Parent of the given ID

Response:

{
  "Size": 512366,
  "Err": ""
}

Respond with the size of the new layer in bytes. Respond with a non-empty string error if an error occurred.

/GraphDriver.DiffSize

Request:

{
  "ID": "46fe8644f2572fd1e505364f7581e0c9dbc7f14640bd1fb6ce97714fb6fc5187",
  "Parent": "2cd9c322cb78a55e8212aa3ea8425a4180236d7106938ec921d0935a4b8ca142"
}

Calculate the changes between the specified ID

Response:

{
  "Size": 512366,
  "Err": ""
}

Respond with the size changes between the specified ID and Parent Respond with a non-empty string error if an error occurred.