[Info-vax] New filesystem mentioned

[Dave Froble]

On 5/14/2019 6:56 AM, John Reagan wrote:
> You seem to keep forgetting about shared access to the allocation bitmap, shared accesses to files, etc.  Sure, any node can $QIO to any block #, but the file system uses locks to synchronize across cluster nodes.  I searched the XQP listings for calls to $ENQ and found at least 50 of them.
>

Well no John, I didn't forget.  I never knew about that.  Nor do I have 
XQP listings.

Not that it surprises me.  Would not access to the allocation bitmap be 
pretty much the same as access to any other part of the disk?  Some 
cooperating sharing is required.

Such things are required in some form in probably all OSs that have 
shared access to storage.  Perhaps in some cases the locking is part of 
the tool.  In the case of the DLM, it's an independent thing that can be 
used by all that need such.  Nice not to have to re-implement the wheel 
every time.

I still remember some conversations with Kirbey Altman who was doing the 
implementation of the DLM, way back.  Some interesting things mentioned 
are still fresh in my mind.  Some serious work went into the design of 
the DLM.  I just wish the designer(s) had considered multiple types of 
locks, and not just locks on a resource name.  I really could have used 
numeric range locking back then.

-- 
David Froble                       Tel: 724-529-0450
Dave Froble Enterprises, Inc.      E-Mail: davef at tsoft-inc.com
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