Re: String getting truncated across OUT link

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

Hi David,

I can demonstrate using either a CA or DB link to have an lso record write a long string to an lsi, but I haven’t used pva: links with long strings before and don’t know if there is a special setting needed to get them to work, or if this is a bug.

Using a CA link you have to add a “$” field modifier to the target PV name, and without the VAL field name you still need a “.” before that, so your first database would become something like this:

    record(lso, "dbracey:src") {

      field(DOL, {const:"Another long string that contains more than 40 characters”})

      field(SIZV, 256)

      field(OUT, "dbracey:tgt.$")

    }

If the src and tgt PVs are in the same IOC that will use a DB link, otherwise it’ll be a CA link.

When I try adding the same field modifier to a pva link PV name, the target IOC prints errors like this:

tgt.$ PVA link put ERROR: Invalid input : "Another long string that contains more t"

That error was from PVXS (QSRV2); QSRV from pva2pva gave me this instead:

tgt.$ PVA link put ERROR: parseToPOD: No digits to convert

- Andrew

-- 

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

On 2/6/26, 2:22 PM, "Tech-talk" <tech-talk-bounces at aps.anl.gov> wrote:

EPICS-BASE 7.0.10

PVXS 1.5.0

Linux version 5.14.0-570.62.1.el9_6.x86_64 (mockbuild at x64-builder03.almalinux.org)

I am trying to use an OUT link to move a string from one IOC to another (lso -> lsi) but the string is getting truncated.

Here are the DB's:

    record(lso, "dbracey:src") {

      field(SIZV, 256)

      field(OUT, {pva:"dbracey:tgt"})

    }

    record(lsi, "dbracey:tgt") {

      field(SIZV, 256)

    }

Both are softIocPVX on the same host (the src IOC gets port 5075, the tgt IOC gets port 37875):

    dbracey@somebox:~$ softIocPVX -d src.db

    INFO: PVXS QSRV2 is loaded, permitted, and ENABLED.

    Starting iocInit

    ############################################################################

    ## EPICS R7.0.10

    ## Rev.

    ## Rev. Date :

    ############################################################################

    iocRun: All initialization complete

    epics>

    dbracey@somebox:~$ softIocPVX -d tgt.db

    INFO: PVXS QSRV2 is loaded, permitted, and ENABLED.

    2026-02-06T13:52:42.521554992 WARN pvxs.tcp.setup Server unable to bind port 5075, falling back to [::]:37875

    Starting iocInit

    ############################################################################

    ## EPICS R7.0.10

    ## Rev.

    ## Rev. Date :

    ############################################################################

    cas WARNING: Configured TCP port was unavailable.

    cas WARNING: Using dynamically assigned TCP port 43047,

    cas WARNING: but now two or more servers share the same UDP port.

    cas WARNING: Depending on your IP kernel this server may not be

    cas WARNING: reachable with UDP unicast (a host's IP in EPICS_CA_ADDR_LIST)

    iocRun: All initialization complete

    epics>

The full string makes it into "dbracey:src" but it is truncated in "dbracey:tgt":

    dbracey@somebox:~$ pvxput dbracey:src "1234567890123456789012345678901234567890123456789X"

    dbracey@somebox:~$ pvxget dbracey:src

    dbracey:src

        value string = "1234567890123456789012345678901234567890123456789X"

        alarm.severity int32_t = 0

        alarm.status int32_t = 0

        alarm.message string = ""

        timeStamp.secondsPastEpoch int64_t = 1770407572

        timeStamp.nanoseconds int32_t = 719494104

        timeStamp.userTag int32_t = 0

        display.description string = ""

    dbracey@somebox:~$ pvxget dbracey:tgt

    dbracey:tgt

        value string = "1234567890123456789012345678901234567890"

        alarm.severity int32_t = 0

        alarm.status int32_t = 0

        alarm.message string = ""

        timeStamp.secondsPastEpoch int64_t = 1770407572

        timeStamp.nanoseconds int32_t = 722877993

        timeStamp.userTag int32_t = 0

        display.description string = ""

Watching the ports with tcpdump shows the full string on the src port, but the truncated string on the tgt port:

    [root@somebox dbracey]# tcpdump -A -i lo port 5075

    <snipped>

    13:59:29.895373 IP somebox.fnal.gov.pvaccess > somebox.fnal.gov.47484: Flags [P.], seq 241:335, ack 133, win 512, options [nop,nop,TS val 1485364043 ecr 1485364043], length 94

    E.../f@.@..-...........|...Y........

    X.....

    X..KX..K..@.V.... ..@....21234567890123456789012345678901234567890123456789X..........G.i....A........

    13:59:29.895417 IP somebox.fnal.gov.47484 > somebox.fnal.gov.pvaccess: Flags [P.], seq 133:203, ack 335, win 512, options [nop,nop,TS val 1485364043 ecr 1485364043], length 70

    E..z..@.@.S..........|..............

    @.....

    X..KX..K....>........ .....21234567890123456789012345678901234567890123456789X

    [root@somebox dbracey]# tcpdump -A -i lo port 37875

    <snipped>

    13:59:29.896946 IP somebox.fnal.gov.37875 > somebox.fnal.gov.35472: Flags [P.], seq 203:287, ack 117, win 512, options [nop,nop,TS val 1485364044 ecr 1485364044], length 84

    E...Pg@.@..5.............(...U......

    N.....

    X..LX..L..@.L.... ..@....(1234567890123456789012345678901234567890..........G.i.............

    13:59:29.896984 IP somebox.fnal.gov.35472 > somebox.fnal.gov.37875: Flags [P.], seq 117:204, ack 287, win 512, options [nop,nop,TS val 1485364044 ecr 1485364044], length 87

    E....U@.@..D.............U...(.`....

    Q.....

    X..LX..L....O........ ......(1234567890123456789012345678901234567890..........G.i.............

Any help would be appreciated.