Record types are the only DBD entries for which the parser
will not accept redefinitions. This change lets it accept
a record type declaration any number of times. However once
a record type declaration has been parsed the full record
type definition cannot be loaded, an error will be raised
if the full definition is seen. The parser will still not
accept a full record type definition more than once either,
any later copies of the record type must be declarations.
If a record type named in a device() entry does not exist when
the device is seen, the DBD parser will now print a warning
and create an empty record type with that name to hold the
device entry information.
This will allow support modules to be built into libraries that
include their own registerRecordDeviceDriver code, which was
apparently possible with 3.14 although not officially supported.
To avoid the warning message, the DBD file can declare each
record type before the device statement that uses it.
A record type declaration looks like this:
recordtype(ao) {}
device(ao, ....)
An IOC will accept and ignore a record type declaration, but it
must have loaded the full record type definition first.
Source DBD files can include Pod blocks, as long as the dbdExpand.pl
script doesn't try and include it in expanded DBD output files.
This makes it easier to write the Pod, and perldoc can parse most
of the result for checking (it complains about the =field directives
though, which dbdToHtml.pl handles itself).
Record types cannot be duplicated however.
DBD sub-objects now have a ->what method for their description.
This also adds a method to look up a breaktable by name.
