From:	MERC::"uunet!CRVAX.SRI.COM!RELAY-INFO-VAX" 23-APR-1992 03:33:49.22
To:	INFO-VAX@KL.SRI.COM
CC:	
Subj:	re: LIB$SPAWN misbehaves, SYS$INPUT not really inherited? [PPF's]

	[I had written that PPF, "process-permanent file", refers to a
	file opened by DCL.  Carl Lydick responded:]
	Actually, it refers to certain files opened by DCL.  SYS$INPUT,
	SYS$OUTPUT, SYS$COMMAND, and SYS$ERROR are the standard PPFs.  You can
	open other files via the DCL OPEN command, but these are NOT PPFs.

Sorry, that's not correct.  According to the VMS Glossary - the only place I
was able to find a formal definition - a process permanent file is "A file
opened or created through ... RMS ... by supervisor or executive mode when
the process permanent bit is set in the file-processing options field."

Less formally, the DCL Concepts book says a PPF is a file that is POTENTIALLY
open for the life of the process.  It lists SYS$INPUT and friends as the
DEFAULT PPF's available to a process.  This is certainly true of a file
OPEN'ed from DCL level.

Files OPEN'ed from DCL level are certainly being accessed at an inner mode,
or they'd be closed at the next user-mode image rundown - but they are not.
What the documentation doesn't tell you is whether DCL sets the process
permanent bit when opening the file.  To be really sure, you'd have to check
the code.

There is, however, another bit of evidence.  The logical names for PPF follow
an escaping convention:  The first four bytes contain Hex 1B, Hex 00, and then
the 16-bit RMS IFI (Internal File Identifier).  The Introduction to System
Services explicitly tells you that the logical name entries for the default
PPF's follow this convention.  It doesn't tell you if ONLY PPF's may follow
this convention.  Still, "escaped logical name" has usually been identified
with PPF in documentation.

Unfortunately, you can't check whether logicals created with OPEN are "es-
caped" from DCL, since SHOW LOGICAL, SHOW TRANSLATION, F$LOGICAL, and F$TRNLNM
all understand the convention and strip the escape sequence.  So you have to
write a little program, which I did - and, sure enough, the logical name that
gets created when you OPEN a file from DCL is "escaped".

							-- Jerry