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<== Date ==> <== Thread ==>

Subject: V4 Access Rights over DataAccess
From: Ralph Lange <Ralph.Lange@bessy.de>
To: "Dalesio, Leo `Bob`" <dalesio@slac.stanford.edu>
Cc: EPICS Core Talk <core-talk@aps.anl.gov>
Date: Wed, 22 Jun 2005 13:04:56 +0200
Dalesio, Leo `Bob` wrote:

Return			id, quality, data_type, number_of_elements, access
					access - do I have access or not
Interesting aspect:

How are we providing access rights information over DA?

Some thoughts:
o Other than with V3 one CA subscription can cover a property catalog containing stuff with different access rights. To be exact, every single property must have an access rights sub-property connected to it. o The property catalog that is used for accessing the data won't carry that information - it should only export readable properties to aViewer and only writeable properties to a Manipulator. (Else it would be throwing exeptions all the time.) o So the probably most natural place for that info is the special descriptive property catalog that is used to find out about the data property catalog structure and native types of its properties. This thing should contain /all/ properties regardless of access rights and carry the access right info with every property. o Will there be a separate callback for access rights change? (The current V4 CA client interface doc says: no.) o So: Clients that want to be notified if access rights change, have to subscribe to ... what exactly? A pseudo property that exists for every property in the catalog? The special desription property catalog? (If this contains the access rights data as mentioned above, it will be updated if access rights change.) Sounds feasible. The description property catalog could (should?) be held internally in the CA client library to spare the client tool from implementing storage for this structure information. Storage would be provided by the Data Store facility. (Alternatively, the client tool could organise storing the structure info itself - probably also by using the Data Store facility. o Will the access security configuration (as it is organised hierarchically) be available or even modifyable through DA?


ps. Please use the mailing list that Andrew announced (<core-talk@aps.anl.gov>) instead of multiple To:-Headers, so that everyone gets the mail and it is archived on the web.
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