Package ganeti :: Package cmdlib :: Module query :: Class LUQuery
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Class LUQuery

source code


Query for resources/items of a certain kind.

Instance Methods [hide private]
 
CheckArguments(self)
Check syntactic validity for the opcode arguments.
source code
 
ExpandNames(self)
Expand names for this LU.
source code
 
DeclareLocks(self, level)
Declare LU locking needs for a level
source code
 
Exec(self, feedback_fn)
Execute the LU.
source code

Inherited from base.NoHooksLU: BuildHooksEnv, BuildHooksNodes

Inherited from base.LogicalUnit: CheckPrereq, HooksCallBack, __init__

Inherited from object: __delattr__, __format__, __getattribute__, __hash__, __new__, __reduce__, __reduce_ex__, __repr__, __setattr__, __sizeof__, __str__, __subclasshook__

Class Variables [hide private]
  REQ_BGL = False

Inherited from base.NoHooksLU: HPATH, HTYPE

Instance Variables [hide private]

Inherited from base.LogicalUnit: dry_run_result

Properties [hide private]

Inherited from object: __class__

Method Details [hide private]

CheckArguments(self)

source code 

Check syntactic validity for the opcode arguments.

This method is for doing a simple syntactic check and ensure validity of opcode parameters, without any cluster-related checks. While the same can be accomplished in ExpandNames and/or CheckPrereq, doing these separate is better because:

  • ExpandNames is left as as purely a lock-related function
  • CheckPrereq is run after we have acquired locks (and possible waited for them)

The function is allowed to change the self.op attribute so that later methods can no longer worry about missing parameters.

Overrides: base.LogicalUnit.CheckArguments
(inherited documentation)

ExpandNames(self)

source code 

Expand names for this LU.

This method is called before starting to execute the opcode, and it should update all the parameters of the opcode to their canonical form (e.g. a short node name must be fully expanded after this method has successfully completed). This way locking, hooks, logging, etc. can work correctly.

LUs which implement this method must also populate the self.needed_locks member, as a dict with lock levels as keys, and a list of needed lock names as values. Rules:

  • use an empty dict if you don't need any lock
  • if you don't need any lock at a particular level omit that level (note that in this case DeclareLocks won't be called at all for that level)
  • if you need locks at a level, but you can't calculate it in this function, initialise that level with an empty list and do further processing in LogicalUnit.DeclareLocks (see that function's docstring)
  • don't put anything for the BGL level
  • if you want all locks at a level use locking.ALL_SET as a value

If you need to share locks (rather than acquire them exclusively) at one level you can modify self.share_locks, setting a true value (usually 1) for that level. By default locks are not shared.

This function can also define a list of tasklets, which then will be executed in order instead of the usual LU-level CheckPrereq and Exec functions, if those are not defined by the LU.

Examples:

 # Acquire all nodes and one instance
 self.needed_locks = {
   locking.LEVEL_NODE: locking.ALL_SET,
   locking.LEVEL_INSTANCE: ['instance1.example.com'],
 }
 # Acquire just two nodes
 self.needed_locks = {
   locking.LEVEL_NODE: ['node1.example.com', 'node2.example.com'],
 }
 # Acquire no locks
 self.needed_locks = {} # No, you can't leave it to the default value None
Overrides: base.LogicalUnit.ExpandNames
(inherited documentation)

DeclareLocks(self, level)

source code 

Declare LU locking needs for a level

While most LUs can just declare their locking needs at ExpandNames time, sometimes there's the need to calculate some locks after having acquired the ones before. This function is called just before acquiring locks at a particular level, but after acquiring the ones at lower levels, and permits such calculations. It can be used to modify self.needed_locks, and by default it does nothing.

This function is only called if you have something already set in self.needed_locks for the level.

Parameters:
  • level - Locking level which is going to be locked
Overrides: base.LogicalUnit.DeclareLocks
(inherited documentation)

Exec(self, feedback_fn)

source code 

Execute the LU.

This method should implement the actual work. It should raise errors.OpExecError for failures that are somewhat dealt with in code, or expected.

Overrides: base.LogicalUnit.Exec
(inherited documentation)