Experimental Physics and
Industrial Control System

[email protected] (Jeff Hill) · Wed, 21 Feb 96 11:29:26 MST

> I have some questions/comments on EPICS "Access Security":
> 
> (1) I wanted to see the effect of stopping a user from accessing
> data values with "dm", by using a suitably set-up access security file.
> It did work. However, I was somewhat surprised by the message returned in
> the "dm" text box which was "No data available". It was only when I looked
> at messages in my command tool that I realised that access was being denied.
> I don't see at present, how the user, just from looking at the "dm" screen could
> tell that access was being denied? Couldn't "dm" be made clever enough to distinguish
> the cases of "No data available" and "Insufficient Access"? At 14,000 ft 
> misleading messages will lead to even greater confusion when a system is
> being debugged!

CA does provide this information to the client library API. However,
it may take awhile before all clients have been updated to use it.

> 
> (2) In another scenario, I was making a database in IOC1 send a command to
> a database in IOC2. By sending a command, I mean writing to a field of a record
> in IOC2 which had ASL = 0 and PP = YES in the ascii file. 
> I found that when the command 
> was blocked by the access security mechanism, the following appeared on the IOC1
> shell (sender of the command):
> 
> ************************************************************************
> task: 0Xe7d640 dbCaOutput
> dbCa_unknownECA ERROR: queue_ca_put() unrecognizable status returned 376
> 
> Bus Error
> Program Counter: 0x00f0bc72
> Status Register: 0x3000
> Access Address : 0xf8609ffc
> Special Status : 0x0485
> Task: 0xe4f338 "process_asynch_events_task"
> ************************************************************************** 
> 
> When I saw "Bus Error" I was rather shocked. Should blocking out access really
> cause such an error to occur in the sending IOC or is this indicative of a
> more serious error?
> 
> I sort of expected a nice message to appear saying "access denied".
> 

This looks like a bug in the db links code (it appears to be unable
to handle an unexpected ca error code - in this case ECA_NOWTACCESS). 

Jeff

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System