[Gluster-devel] Glusterd daemon management code refactoring

[Atin Mukherjee]

On 12/09/2014 06:24 PM, Jeff Darcy wrote:
>> I would like to propose refactoring of the code managing
>> various daemons in glusterd. Unlike other high(er) level proposals
>> about feature design, this one is at the implementation
>> level. Please go through the details of the proposal below
>> and share your thoughts/suggestions on the approach.
> 
> I like this idea, as a way of reducing technical debt.  Can we take it a
> step further, and provide default *implementations* for some of these
> methods?  For example, connect/disconnect and is_running are likely to
> be the same for practically all daemons.
We do have a plan to implement the default implementations.

> 
>> ### Introduction
>>
>> Glusterd manages GlusterFS daemons providing services like NFS, Proactive
>> self-heal, Quota, User servicable snapshots etc. Following are some of the
>> aspects that come under daemon management.
>>
>> - Connection Management
>>   - unix domain sockets based channel for internal communication
>>   - Methods - connect, disconnect, notify
>>
>> - Process Management
>>   - pidfile to detect if the daemon is running
>>   - Environment; run-dir, svc-dir, log-dir etc.
>>   - Methods - start, stop, status, kill
>>
>> - Daemon-specific Management
>>
>> Currently, the daemon management code is fragmented and doesn't elicit the
>> structure described above. This results in further fragmentation since new
>> developers may not identify common patterns, worse even, they won't be able
>> to
>> do anything about it.
>>
>> This proposal aims to do the following,
>>
>> - Provide an abstract data type that encapsulates what is common among
>> daemons
>>   that are managed by glusterd.
>>
>> - 'Port' existing code to make use of the abstract type. This would help in
>>   making this change self-documented to an extent.
>>
>> - Prescribe a way to maintain per-feature daemon code separate to glusterd's
>>   common code.
>>
>> ### Abstract data types
>>
>>         struct conn_mgmt {
>>             struct rpc_clnt *rpc;
>>             int (*connect) (struct conn_mgmt *self);
>>             int (*disconnect) (struct conn_mgmt self);
>>             int (*notify) (struct conn_mgmt *self, rpc_clnt_event_t
>>             *rpc_event);
>>         }
>>
>>         struct proc_mgmt {
>>             char svcdir[PATH_MAX];
>>             char rundir[PATH_MAX];
>>             char logdir[PATH_MAX];
>>             char pidfile[PATH_MAX];
>>             char logfile[PATH_MAX];
>>
>>             char volid[UUID_CANONICAL_FORM_LEN];
> 
> How about a PID, so that default implementations (e.g. is_running
> or kill) can use it?
pidfile will have the details for it.

> 
>>             int (*start) (struct proc_mgmt *self, int flags);
>>             int (*stop) (struct proc_mgmt *self, int flags);
>>             int (*is_running) (struct proc_mgmt *self);
>>             int (*kill) (struct proc_mgmt *self, int flags);
>>
>>         }
>>
>> Feature authors can define data type representing their service by
>> implementing
>> the above 'abstract' class. For e.g,
>>
>>         struct my_service {
>>             char name[PATH_MAX];
>>             /* my_service specific data members and methods */
>>
>>             /* The methods in the following structures should be implemented
>>             by
>>                respective feature authors */
>>
>>             struct conn_mgmt conn;
>>             struct proc_mgmt proc;
>>         }
>>
>> ### Code structure guidelines
>>
>> Each feature that introduces a daemon would implement the abstract data type.
>> The implementations should be in separate files named appropriately. The
>> intent
>> is to avoid feature specific code to leak into common glusterd codebase.
>> glusterd-utils.c is testament to such practices in the past.
>>
>> For e.g,
>> [kp at trantor glusterd]$ tree
>> .
>> └── src
>>     ├── glusterd-conn-mgmt.c
>>     ├── glusterd-conn-mgmt.h
>>     ├── glusterd-proc-mgmt.c
>>     ├── glusterd-proc-mgmt.h
>>     ├── my-feature-service.c
>>     └── my-feature-service.h
>>
>> [kp at trantor glusterd]$ cat src/my-feature-service.h
>>         #include "glusterd-conn-mgmt.h"
>>         #include "glusterd-proc-mgmt.h"
>>
>> ...
>> [rest of the code elided]
>>
>> ### Bibliography
>>
>> - Object-oriented design patterns in the kernel, part 1 -
>> http://lwn.net/Articles/444910/
>> - Object-oriented design patterns in the kernel, part 2 -
>> http://lwn.net/Articles/446317/
>>
>>
>> thanks,
>> kp
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>>
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~Atin