etcd/Documentation/etcd-file-system.md

#Etcd File System

Structure

[TODO]

Node

In Etcd, the Node is the rudimentary element constructing the whole. Currently Etcd file system is comprised in a Unix-like way of files and directories, and they are two kinds of nodes different in:

• File Node has data associated with it.
• Directory Node has children nodes associated with it.

Besides the file and directory difference, all nodes have common attributes and operations as follows:

Attributes:

• Expiration Time [optional]

  The node will be deleted when it expires.

• ACL

  The path of access control list of the node.

Operation:

• Get (path, recursive, sorted)

  Get the content of the node

  • If the node is a file, the data of the file will be returned.
  • If the node is a directory, the child nodes of the directory will be returned.
  • If recursive is true, it will recursively get the nodes of the directory.
  • If sorted is true, the result will be sorted based on the path.

• Create (path, value[optional], ttl [optional])

  Create a file. Create operation will help to create intermediate directories with no expiration time.

  • If the file already exists, create will fail.
  • If the value is given, set will create a file.
  • If the value is not given, set will crate a directory.
  • If ttl is given, the node will be deleted when it expires.

• Update (path, value[optional], ttl [optional])

  Update the content of the node.

  • If the value is given, the value of the key will be updated.
  • If ttl is given, the expiration time of the node will be updated.

• Delete (path, recursive)

  Delete the node of given path.

  • If the node is a directory:
  • If recursive is true, the operation will delete all nodes under the directory.
  • If recursive is false, error will be returned.

• TestAndSet (path, prevValue [prevIndex], value, ttl)

  Atomic test and set value to a file. If test succeeds, this operation will change the previous value of the file to the given value.

  • If the prevValue is given, it will test against previous value of the node.
  • If the prevValue is empty, it will test if the node is not existing.
  • If the prevValue is not empty, it will test if the prevValue is equal to the current value of the file.
  • If the prevIndex is given, it will test if the create/last modified index of the node is equal to prevIndex.

• Renew (path, ttl)

  Set the node's expiration time to (current time + ttl)

ACL

Theory

Etcd exports a Unix-like file system interface consisting of files and directories, collectively called nodes. Each node has various meta-data, including three names of access control lists used to control reading, writing and changing (change ACL names for the node).

We are storing the ACL names for nodes under a special ACL directory. Each node has ACL name corresponding to one file within ACL dir. Unless overridden, a node naturally inherits the ACL names of its parent directory on creation.

For each ACL name, it has three children: R (Reading), W (Writing), C (Changing)

Each permission is also a node. Under the node it contains the users who have this permission for the file refering to this ACL name.

Example

[TODO]

Diagram

[TODO]

Interface

Testing permissions:

• (node *Node) get_perm()
• (node *Node) has_perm(perm string, user string)

Setting/Changing permissions:

• (node *Node) set_perm(perm string)
• (node *Node) change_ACLname(aclname string)

User Group

[TODO]