Experimental Physics and
Industrial Control System

[email protected] (Marty Kraimer) · Thu, 21 Sep 1995 10:41:53 -0500

Tim Mooney has pointed out a problem with get_units.
The problem is as follows:

Many record types define EGU to have 16 characters.
The record support modules get_units routine executes the statement:

   strncpy(units,prec->egu,sizeof(prec->egu));

Thus the record support module copies up to 16 characters.
However old and new database access only have 8 characters for units.

It turns out that getting units values via channel access NEVER overwrite
anything that is not updated AFTER the strings are copied. Thus the only
result is that channel access clients only get a max of 8 characters.
If 8 characters are obtained it probably is NOT null terminated.

I a database link asks for units info in a buffer that does not have
sufficient extra space after the DBRunits info bad things could happen.
No standard epics record/dev support asks for units info via database
options thus no problem can occur.

We can NOT change the sizes in old or new database access without recompiling
ALL Ca clients AND all ioc software. Thus we cant really do this until we
go to a new major release number of EPICS.

What we can do for now is to define a symbol MAX_UNITS_SIZE in dbDefs.h
and change all record support modules and ascii files to use this symbol.
Then when we go to next major EPICS release number we can just change
MAX_UNITS_SIZE and have everything automatically support units strings
of 16 characters.

Comments?

Marty Kraimer

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System