Experimental Physics and
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Why not put the aliasing in a PV gateway? The disadvantage of using a gateway for aliasing is that you now have the relevant PV names listed in two places, so if you do eventually change the name of the original PV (because everyone is now using the alias) you have to remove it from the gateway configuration as well as change it in the IOC, and these changes have to be synchronized. You might also want to avoid running large arrays or quickly changing signals through a PV gateway for performance reasons; there is no performance effect of doing aliasing on the IOC (other than to the PV name lookup process). Access Security could also be a problem through a PV gateway. On Mon, 2007-10-08 at 10:01 -0400, Lawrence T. Hoff wrote:I may have been the one who initiated the discussion a few years ago. I encountered a situation which I believed was best addressed using server-side aliases. I created a patch to EPICS core (which could be loaded into a VxWorks system as a separate module), which implemented server-side aliases. See http://www.aps.anl.gov/epics/tech-talk/2003/msg00707.php for Larry's original posting, although I do not recommend using this code verbatim. P.S. As near as I could tell, there was not universal enthusiasm for server-side aliases at that time. Maybe at next week's EPICS collaboration meeting the discussion could begin anew? PV Aliasing has been on my "To Do" list for Base for quite a while (my boss wants it too), prompted by your demonstration that it's not hard to do with the current data structures. The important question arises as to whether we need the ability to add aliases after iocInit() â I would guess not often, but I can see circumstances where it would be useful. The only issues remaining that I can see would be a review of database locking (if we allow addition of aliases to a running IOC) and Access Security issues, and to decide how to specify the aliases to the IOC. I would prefer to extend the DB file syntax rather than use something like Larry's addPvAlias(name, alias) command, but adding alias support to dbLoadRecords() might preclude runtime aliasing. I hope we'll be able to make some progress on implementing aliasing (amongst other things) at the EPICS Codeathon next April. - Andrew -- When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong. -- Arthur C. Clarke
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ANJ, 10 Nov 2011 |
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