Re: Usage of pvlist

["Johnson, Andrew N. via Tech-talk" <tech-talk@aps.anl.gov>]

On 7/3/19 10:10 AM, Shen, Guobao via Tech-talk wrote:

I am trying to use pvlist to discover all PVs served thru pvAccess.

Let’s say that I have a few soft EPICS7 IOC running on one machine on different ports, for example:

$ pvlist

GUID 0xA21BC25C0000000083EAFA2C, version 1: tcp@[192.168.10.20:60605]

GUID 0xBA1BC25C00000000ACD90824, version 1: tcp@[192.168.10.20:60607]

GUID 0xBBB91C5D000000005646DE0A, version 1: tcp@[192.168.10.20:58861]

GUID 0xD71BC25C00000000E55F910B, version 1: tcp@[192.168.10.20:60608]

 

I can use pvlist IP:port to get the PVs served thru QSRV on that specific port.

If I use “pvlist IP”, it gives me the PVs only on the first port it found (looks like).

 

Is that a way to find all PVs on different ports instead of looping thru all ports individually?

The code for the pvlist program has the ability to query multiple servers in a single run (provided you explicitly list the servers), but the loop to do so is currently disabled so it stops after printing the first list of PVs that it successfully retrieves.

It is straightforward to re-enable the loop, which lets you give a list of GUIDs or IP:port numbers on the command-line to be queried. That requires applying this change to modules/pvAccess:

diff --git a/pvtoolsSrc/pvlist.cpp b/pvtoolsSrc/pvlist.cpp
index dc6a029..58d2b45 100644
--- a/pvtoolsSrc/pvlist.cpp
+++ b/pvtoolsSrc/pvlist.cpp
@@ -702,11 +702,10 @@ int main (int argc, char *argv[])
                 std::copy(val.begin(),
                           val.end(),
                           std::ostream_iterator<std::string>(std::cout, "\n"));
-
-                return allOK ? 0 : 1;
             }
-
-            std::cout<<ret<<"\n";
+            else {
+                std::cout<<ret<<"\n";
+            }
         }
     }
 

With that change in place, one way to list all visible PVA PVs is this shell one-liner:

tux% pvlist `pvlist | awk '{print $2}'`
C2:SIM7:Pva1:Image
C2:SIM8:Pva1:Image
C2:CTLS:Scope:Data
C2:SIM9:Pva1:Image

It runs pvlist twice, once to get the GUIDs and then again to get the PV names. This could be dangerous since it would be easy to overload a network with a large number of PVA servers, but the equivalent one-liner without the loop inside pvlist is this (which runs pvlist as many times as you have active PVA servers plus one and is somewhat slower):

tux% pvlist | awk '{print $2}' | xargs -L 1 pvlist
C2:SIM7:Pva1:Image
C2:SIM8:Pva1:Image
C2:CTLS:Scope:Data
C2:SIM9:Pva1:Image

I thus don't see a strong reason to not enable the loop by applying the above change.

- Andrew

-- 
Complexity comes for free, Simplicity you have to work for.