Re: EPICS naming services

[Andrew Johnson <anj@aps.anl.gov>]

Luedeke Andreas wrote:
> at the SLS we upload the channels at boot time from the IOC to an oracle 
> table. This is done by a perl script running on the boot pc started by 
> the ioc using rsh, reading a file generated before by the IOC using the 
> dbl command. Not quite the portability you would like to have for epics 
> 3.14 applications: you need to save a file from the IOC and you need to 
> have an rsh mechanism.

The rsh mechanism is not essential if you arrange to have a program 
running on the fileserver which is monitoring all of the dbl output files; 
when it notices a change it triggers the update sequence.  If you're not 
so worried about short delays you could also just have a cron job that 
periodically checks for updates.  This might also be more appropriate if 
the processing after a reboot can take a long time to run, as you can 
limit how often the processing can be started.

Bear in mind that the list of PVs (i.e. CA Channel names) is not the same 
as the output from dbl, which just gives you the record names.  A truly 
omniscient nameserver would also need to know the record type, and the set 
of publicly accessible field names for that record type on that particular 
IOC [don't forget that two IOCs that use two different DBD files can have 
a different set of fields in the same record type, you must make sure 
you're using the IOC's DBD file to be sure what fields it will have].  A 
simple way to resolve this would be to dump the DBD file at boot time as 
well as the dbl output.

It should be relatively straightforward to write some IOC-side code which 
queries the database in memory using dbStaticLib routines, and sends the 
results directly to the name server; I'm not aware of anyone who has 
actually implemented something like this though.  This code would be able 
to resolve the field names issue without having to write a parser to 
extract the DBD filename(s) from the st.cmd file.

- Andrew
--
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