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@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@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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>> Gluster-devel@xxxxxxxxxxx
>> http://supercolony.gluster.org/mailman/listinfo/gluster-devel
>>
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~Atin
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