.TL
Changes in the Kernel in 4.1bsd
.sp
May 10, 1981
.br
Revised: September 1, 1981
.AU
Bill Joy
.AI
Computer Systems Research Group
University of California, Berkeley
.PP
This document summarizes the changes in the kernel
between the November 1980 4.0bsd release and the and
April 1981 4.1bsd distribution.  The information is presented
in both overall terms (e.g. organizational changes), and as
specific comments about individual changed files.  See
the source code itself for more details.
.PP
The major changes fall in five categories:
.IP 1)
Changes in the VAX 11/780 specific portions of the code, so that
VAX 11/750's are supported also.
.IP 2)
Changes in the organization of the code, so that more than one
configuration of the system may be built from a single set of sources.
Each system is described by a single file which includes parameters
such as system size, devices on the machine, etc.
All ``magic numbers'' such as device register addresses are collected
in this single file.
.IP 3)
Extensive changes in the device subsystem to allow multiple UNIBUS
and MASSBUS adapters to be used, multiple instances of device controllers
to exist without duplicating driver code, and to provide the capability
of system configuration at boot time.  The configuration capability
is used to produce a generic system which runs on all supported hardware,
and is used for distributions.  Pattern matching in the configuration
capability also allows hardware redundancy to be used to good effect.
.IP 4)
Diagnostics of the system have been reworked to be in a standard and
readable format; file system diagnostic refer to the file systems by
name rather than device number.  Device diagnostics refer to the devices
by name, and print error messages including device registers decoded
symbolically rather than simply in octal or hexadecimal.
DEC standard bad sector forwarding has been added to the drivers for DEC disks.
.IP 5)
Performance improvements, noticeably in the paging subsystem.
.PP
A number of enhancements and bug fixes have also been made.
.SH
Carrying over local software
.PP
The majority of local changes should carry over to the new system
quite easily.  It it necessary to create a configuration file for each
machine from which a system will be built, but this is quite easy,
and such files are designed to be usable without change in future
releases of the system.
.PP
Locally written UNIBUS device drivers will need to be converted to
work in the new system.  The new functions needed of the device drivers are:
.IP 1)
Forcing a device interrupt at bootstrap time, given a proposed
device register address.  This is used by the configuration program
to decide if the device really exists.
.IP 2)
If buffered data paths are to be used, the driver must use routines
in the UNIBUS adapter subsystem which arranges for i/o requests to be
queued when there are no resources available.
.IP 3)
Drivers must not assume that only one instance of a device exists in the
system, but must rather be parameterized and use the information provided
by the bootstrap procedure to drive all available devices.
.PP
Of course, it is not necessary to make a driver ``fully supported'' for it
to be used.  It suffices to handle 1) by pretending that the interrupt
occurred, returning the (for a single system) known UNIBUS vector information,
and assuming that the device exists on specific UNIBUS adapters.
Drivers which use UNIBUS resources only statically or not all all need
not be concerned with 2), and drivers can assume that there is only one
instance of the supported device on the system, and just not work
if more than one such device is really present.
.PP
In any case, more information about device driver changes is given in the
last section of this document;
also see \fIautoconf\fR\|(4) for information about the messages
printed out by the configuration code at bootstrap time.
Looking at the provided standard
supported drivers for examples of code is also a good idea.
.PP
There is also a new interface for MASSBUS devices.  Since all MASSBUS
devices are already supported, there is no external documentation for writing
new MASSBUS drivers at the present.  If you have questions or intend
to write a driver for a home-brew interface, you should read the MASSBUS
and MASSBUS device driver code, which is amply commented.  In any case,
the MASSBUS interface is more stylized than the UNIBUS interface, and you
may have to extend the functionality of the MASSBUS driver to handle radically
different devices.
.SH
Organizational changes
.PP
On RK07 systems the source for the system lives in the root directory,
since there is so little space.  The system otherwise lives where it
used to: the subdirectories of /usr/src/sys, with copies of the header
files for the installed system in /usr/include/sys.
.PP
The system compilation procedure has been changes so that more than
one set of binaries may be kept conveniently with a single copy of the
source code.  The system sources are kept in the directories \fBsys/sys\fR
and \fBsys/dev\fR with the header files in \fBsys/h\fR.  Source files
which were previously kept in \fBsys/conf\fR are now in \fBsys/dev\fR,
and no binaries are kept in any of these directories.
.PP
The directory
\fBsys/conf\fR contains a number of files related to system configuration.
For each machine to be configured, a single file is created in the
\fBsys/conf\fR directory; thus files \fBERNIE\fR and \fBBERT\fR might
exist there.  Each such file describes all the parameters of the machine
to be used: the devices which are to be configured into the system, optional
parts of the system to be included, as well as the timezone in which
the machine lives and the maximum number of simultaneous active users; the
last is used to scale system tables.
The format of the configuration files is described in \fIconfig\fR\|(8).
.PP
Corresponding to each system to be configured there is a directory of
\fBsys\fR, thus \fBsys/BERT\fR and \fBsys/ERNIE\fR.  These directories
are made with \fImkdir\fR and then the \fB/etc/config\fR command is run,
from the \fBsys/conf\fR directory, specifying \fBBERT\fR or \fBERNIE\fR
as argument.  The configuration program processes the information in
the configuration files, and produces, in the directory \fB../BERT\fR or
\fB\&../ERNIE\fR respectively:
.IP 1)
A set of header files, e.g. \fBdz.h\fR, which contain the number of devices
and controllers to be available in the target system.  These definitions
force conditional compilation of drivers resulting in the inclusion
or exclusion of driver code and the sizing of driver tables.  This
technique, based on compilation, is more powerful than a loader-based
technique, since small sections of code may be easily conditionalized.
Similarly, dynamic loading of device drivers is not needed, as only
drivers which are needed are included in the resulting system.
.IP 2)
A small assembly language vector interface, which turns the
hardware generated UNIBUS interrupt sequences into C calls on the
driver interrupt routines.  This \fBubglue.s\fR file glues the hardware
interrupt sequence into the UNIX interface.
.IP 3)
A table file \fBioconf.c\fR which initializes tables to be
used at bootstrap time by the system configuration routines.  The configuration
routines interpret the contents of the table and determine which devices
are available on the system.  They determine the vector addresses of UNIBUS
devices by forcing the devices to interrupt.  Pattern matching in the tables
may be used to take advantage of hardware redundancy: the specifications
need not completely constrain device placement, so the system can be built
to bootstrap in several different configurations, locating the same devices
on different interconnects by the fact that their unit numbers have not
changes (for example).  Thus two RP06 disks could be specified as:
.DS
disk hp0 at mba? drive 0
disk hp1 at mba? drive 1
.DE
and then the disks could be cabled to any available MASSBUS adapter; the
pattern matching in the configuration procedure would locate the drives.
Similarly, a tape formatter on the same system could be specified:
.DS
master ht0 at mba? drive ?
.DE
and then placed anywhere on any MBA.
Contrast this flexible specification with
.DS
disk hp0 at mba0 drive 0
disk hp1 at mba0 drive 1
master ht0 at mba1 drive 0
.DE
which is not reconfigurable.  This latter specification corresponds
to the previous UNIX capabilities, which did not allow tapes and disks
on the same MASSBUS adapter.
.IP 4)
Finally the \fIconfig\fR program constructs a \fImakefile\fR
for the system which builds the drivers needed in the specified configuration,
and includes system loading sequences for the different root and swap
device configurations desired.
.PP
It is now easy to include ``subsystems'' optionally.  This is done
through the same mechanisms which causes conditional inclusion of device
drivers.  The file \fBconf/files\fR contains a palate of files which
builds the system.  Each line is either of the form:
.DS
filename	standard
.DE
or
.DS
filename	optional \fIxx\fR
.DE
where \fIxx\fR is the name of a device which requires the file, or a
\fIpseudo-device\fR.  To define a subsystem to be added to the kernel
it suffices to add specifications to the \fBconf/files\fR file for the
newly optional files and to then place a specification
.DS
pseudo-device	\fIxx\fR
.DE
in the system configuration file.  A line
.DS
options	\fIXX\fR
.DE
may also be added to the configuration
to have the symbol XX defined during compilation,
for use in conditional compilations in the standard part of the system.
Such conditional compilation is typically used to provide hooks in the
standard part of the kernel to switch out to subsystem functions.
.PP
This completes the general description of organizational changes.
We now describe the changes in the system, file by file.
.SH
Header files: sys/h and /usr/include/sys
.PP
General changes: device drivers now have header files in these
directories, thus the ``up'' driver has a header file ``upreg.h''.
This so the standalone code and the mainline UNIX code can share
the common definitions.
.PP
The ``.m'' files of the previous distribution
have been eliminated (with the sole exception of \fBpcb.m\fR); the
magic numbers which were manually entered in these files are instead
generated by a program from the definitions in the corresponding
\fB\&.h\fR files; a number of header files thus no longer warn about
correspondences that must be maintained.
.PP
The system tables are now described by pointers to their beginning
and end and a count, rather than compiled in constants.  This allows
table sizes to be chosen at boot time (although the system currently
does this only for the file system buffer cache), and makes programs
such as \fBps\fR and \fBw\fR not compile in these constants.  Note,
especially, that the symbols such as \fIproc\fR and \fIinode\fR are
now memory locations containing the addresses of these structures
rather than the base of the structures themselves.  Programs which
access these structures have been changed and use the variables \fInproc\fR
and \fIninode\fR in core rather than the (now defunct) constants NPROC
and NINODE.
.de BP
.IP \\fB\\$1\\fR 14n
..
.BP buf.h
Now declares three headers on which the in-core buffers are placed.
Buffers which are locked in the buffer cache are placed on the first
queue.  Currently, only file system super blocks are locked in core,
and to good effect: it is now possible to rebuild the super-block of
the root file system with the system quiescent (without rebooting) if
the block device is used.  It is no longer necessary to take a buffer
for the super-block of a file system and also make a copy of it at
each sync; the same buffer can be reused and simply released: since it
is locked it will remain in the buffer cache.
.IP
The other two queues implement the lru cache and the list of blocks
which have been discarded.  By having queues for both of these rather
than using the end of a single queue, we achieve true fifo behavior for
blocks which we consider ``discarded''; previously rather strange behavior
resulted from pushing these blocks backwards on the front of the single
queue.  (In particular pipes would behave badly on idle systems under
some circumstances.)
.IP
The number of pages paged is counted at pageout completion, as well
as the pageout event count.  A bug in the \fBphysio\fR routine which
caused physical transfers of more than 60000 bytes to sometimes
fail to return an error indication has been fixed.
.IP
A flag has been added that marks a buffer as consisting only of a header
and also one which marks a buffer being used for bad-sector processing.
.BP callo.h
Is now called \fBcallout.h\fR, and the name of the structure is similarly
changed to make it consistent with the other structures in the kernel.
The structures are now linked together in linked lists, to prevent arcane
situations previously possible where only half of the structures would
be used, but the table space would be exhausted.
.BP clock.h
A botch in handling of leap years has been fixed.  A macro is defined
here to queue a software interrupt for handling most of the clock
processing at an IPL lower than the clock IPL.
.BP cmap.h
This file, like a number of others, no longer warns that the size
of the structure is known elsewhere; such dependencies are the concern
of a C program and automated through makefile dependencies.
.BP conf.h
A \fId_dump\fR entry has been added to the block device table, and is
used as the system now normally does automatic dumps of core memory to disk
after a crash.  The field \fId_tab\fR is now called \fId_flags\fR and
set to B_TAPE for tapes.  For reasons not worth explaining here, there
are no ``tab'' structures to sensibly use in initializing this field now,
and in any case the only use of it was to tell which block devices were tapes.
.BP dkbad.h
Is a new file which defines the format of the bad sector forwarding
information according to DEC standard 144.
.BP dmap.h
The constant DMMIN has been increased to 32 to allow upto 16k bytes to be
paged to the paging devices in a clustered pageout.
.BP filsys.h
The two fields \fIs_fname\fR and \fIs_fpack\fR which were not implemented
before were merged together (into a single 12 character field) which
is called \fIs_fsmnt\fR.  The system puts the ASCII path name where a file
system is mounted (e.g. /usr) in this field and uses it in printing error
messages on the console; (e.g. ``/usr: file system full'' rather than
``no space on dev 0/6'').
.BP inline.h
In order to reduce the number of conditional flags defined when compiling
the system, the conditional flag FASTVAX, which was always defined,
has been deleted.  A conditional flag UNFAST, which is never defined, has been
added to take its converse's place.
.BP inode.h
The constant NINDEX has been reduced from 15 to 6.  This limits the number
of files which may be join()'ed into a multiplexor (\fImpx\fR\|(2)) tree.  You
may have to increase this if you use the multiplexor extensively, but it
saves a large amount of space in the kernel if you can use the smaller value,
since NINDEX of 15 causes 40 bytes of extra unused space to be allocated
to every inode.
.BP map.h
The \fBmalloc.c\fR routines have been rewritten to check for table
overflow and renamed \frmap.c\fR.
.BP mba.h
Is now split into \fBmbareg.h\fR and \fBmbavar.h\fR, the former contains
the definitions of device register and is usable, e.g., in the standalone
version of the system.  The latter contains system variable related to the
MASSBUS adapters.
.BP mem.h
Is a new file which contains information on the memory controller registers
in the form of macros which make the several VAX processors seem very
similar to the UNIX code.  Note also that the system now uses interrupts
from the memory system to force error logging since the previous technique
(polling) works only on the 11/780.
.BP mscp.h
A new file which defines the DEC \fIMass Storage Control Protocol\fR
used by the UDA50 disk controller.
.BP mtpr.h
The register numbers are now given in hex, as in the DEC manuals; registers
for all VAX processors are included.
.BP msgbuf.h
Defines the structure of the error message buffer, which is now kept
in the last 1024 bytes of memory.  This allows it to be preserved
across system crashes and lets messages such as machine check reports
be written conveniently into the error log.
.BP nexus.h
A new header file which defines the registers and constants related
to the interconnect architecture of VAXen.
.BP param.h
No longer defines the large number of constants related to system sizing;
a smaller number of rarely changed constants are given here.  In particular,
constants which were typically changed to affect the maximum number
of supportable users are now controlled by the value given the \fBmaxusers\fR
keyword in the machine specification (as described in \fIconfig\fR\|(8)).
The \fIconfig\fR program turns this specification into parameters to the
\fBparam.c\fR file which uses formulae to compute the values for the
size of the process table, inode table, etc.
.IP
This file now includes the standard file <sys/types.h> to get system
types rather than replicating the definitions from that file.  It also
defines a DELAY(n) macro which is used in device drivers to provide
rougly \fIn\fR microseconds of delay.  Finally the definition of UPAGES,
the number of system control pages per-process has been increased from 6 to 8.
This is partially due to the fact that there is now a red-zone page between
the kernel stack and the kernel critical data in the \fIu.\fR area,
but also because the kernel stack
was precariously close to being too small before.
.BP pcb.h
Now includes definitions related to the use of AST's to implement user program
profiling and rescheduling.  Because AST's are now used, it is no longer
necessary to take clock interrupts on the kernel stack; they now run on
the interrupt stack where they belong.  Also rescheduling processing
is much cleaner, since the reschedule interrupts only go off when returning
to user mode, not in the kernel where they have to be ignored (because
UNIX cannot reschedule when running normally in the kernel.)
.BP proc.h
Now defines SOWEUPC, a new flag used to indicate that a profiling count
should be generated when the (already posted) AST for this process goes off.
Another new flag SSEQL indicates that the process has declared sequential
paging behavior for its data space.  Finally the field \fBp_maxrss\fR
has been added, specifying the declared ``memoryuse'' limit in pages.
.BP psl.h
Has a bug fixed in the definitions of PSL_USERCLR.  Now also declares
PSL_USERSET and PSL_MBZ (must-be-zero).
.BP system.h
Defines the variables \fIhz\fR, \fItimezone\fR and \fIdstflag\fR replacing
the old compile-time constants.  No longer declares \fImsgbuf\fR as a variable
(see \fBmsgbuf.h\fR).  Defines the \fIdumpdev\fR and \fIdumplo\fR variables
which specify where dumps are to take place.  No longer defines the
debugging variables \fIprintsw\fR and \fIcoresw\fR which have been removed
in favor of more local debugging variables.  No longer defines the field
\fIsy_nrarg\fR for the system call entry structures, since system calls
never take register arguments on the VAX.
.IP
A variable \fBwantin\fR has been added which is set each time a process
is woken up which wants to be swapped in.  This is used so that
the code in \fBswapout\R in \fBvmsched.c\fR does not run with elevated
priority.
.BP trap.h
Rearranges some codes previously used only internally so they would
be contigous numerically.  These are the finer machine traps which result
in SIGILL and are made available to a signal handling process and defined
in <signal.h>.  Defines ASTFLT rather than RESCHED, since the VMS software
interrupt which is used for VMS rescheduling never was appropriate for UNIX
and is no longer used.
.BP uba.h
Has been split into \fBubareg.h\fR and \fBubavar.h\fR; see the description
of device driver changes below.
.BP user.h
Contains definitions related to the new \fB#!\fR exec facility.  The field
\fIu.u_cfcode\fR has been renamed \fIu.u_code\fR since it is now used for
purposes other than compatibility mode (presenting the more precise
hardware reason for SIGILL and SIGFPE signals.)
.BP vlimit.h
Now defined LIM_MAXRSS for the ``limit memoryuse'' feature.
.BP vm.h
The \fBvm*.h\fR headers have been compressed into a more sensible set
of files; the macros are all in \fBvmmac.h\fR (absorbing \fBvmclust.h\fR and
\fBvmklust.h\fR), metering stuff is all in  \fBvmmeter.h\fR (absorbing
\fBvmmon.h\fR and \fBvmtotal.h\fR) and the parameters are all in
\fBvmparam.h\fR (absorbing \fBvmtune.h\fR, most of the parameters
of which are now adjusted at boot time in \fIsetupclock\fR in \fBvmsched.c\fR.)
.BP vmmeter.h
The structure \fBvmmeter\fR now computes the number of pages paged in
\fIv_pgpgin\fR and pages paged out \fIv_pgpgout\fR, as well as the 
number of pages freed because of the behavior of programs which have
told the system they are sequential \fIv_seqfree\fR.
.BP vmparam.h
The values of MAXDSIZ and MAXSSIZ have increased due to the increase to
DMMIN in \fBdmap.h\fR.
The klustering constants have been changed: in-clustering is now in 4 page
(4k byte) chunks, and out-clustering is up to 16k bytes.  Sequential programs
kluster in 8k bytes, and text segments kluster in 2k bytes.  The gap
for the window into sequential programs is currently (primitively) defined
as a constant kere in KLSDIST.
.BP vmsystm.h
Defines a new variable \fIavefree30\fR, which computes the average memory
like \fIavefree\fR, but averaged over a longer period of time.  This
is used to put more hysteresis into swapping, and keep the system
from swapping immediately when memory drops low.
.SH
System files: sys/sys
.PP
A number of files in the system have had minor changes made to them
to reduce the length of time the system runs with the interrupt
priority level raised; in particular, the times when the IPL is high
enough to block the clock have been severely limited, in hopes
of providing better real-time response (eventually) and possibly
being able to drive the 11/750 console cassette (soon) which has
severe interrupt latency constraints due to poor hardware interface design.
.BP acct.c
The code was tightened by using a register variable.
The \fIsysphys\fR routine was moved to \fBsys4.c\fR since
it had no business being here.
.BP alloc.c
Prints error messages relating to file system problems
using the name of the file system rather than the major/minor
device number of the device.  Some code which attempted to prevent
``dups in free'' after a reboot, but could not prevent this completely,
has just been removed; the condition is not harmful in any case, as it
is normal and fixed by \fIfsck\fR\|(8).  The system now prints directly
on a user's terminal if that user causes a file system to run out of free
space.  The routines here also know how to deal with the fact that the
super-blocks are now kept locked in the buffer cache.
.BP asm.sed
No longer defines \fIspl1\fR which is now defunct; \fBspl7\fR is now
VAX IPL 0x1f rather than 0x18, blocking most processor aborts
device interrupts from the console storage device, and a number
of other processor dependent interrupts.  Deals with
a strange feature of the optimizer which converts ``$0'' into a register
which contains 0.  Implements the \fIffs\fR routine of \fBsig.c\fR
in a much more efficient way (in just a couple of VAX instructions.)
Beware, however: UNIX's notion of \fIffs\fR returns 1 for the low
bit of a word, while the hardware \fIffs\fR would return 0.
.BP clock.c
Now runs only that code which is absolutely necessary when the processor
priority is very high, queueing a software interrupt at which priority
the rest of the clock processing is done.  The conditional
(old and long unused) code which profiled the kernel in a static 
buffer has been removed.  The option of fishing characters out of the
\fIdz\fR and \fIdh\fR silo's less often than every clock tick (1/hz)
has been removed.  Instead the silos are processed every clock tick if
the system includes the berknet (bk) line discipline, or not at all
(i.e. we take input interrupts) if ``bk'' is not included in the system.
.IP
The processing and watching of hung UNIBUS adapters has been moved from
here to the UNIBUS routines.  Automatic niceing of long-running (more than
10 minutes of user-state time) processes is now the default here, rather
than being based on ``#if ERNIE''.  A bug in the check for timeout table
overflow which would cause the table to overrun without overflow
being detected has been fixed.  The timeout table is now implemented
as a linked list, so that the entries can be conveniently discarded
before calling the timeout routines.  This prevents the anomalous
case where only half the entries are used but the table fills up.
.BP fio.c
Has been changed to do the correct thing when special files or mounted
file systems are closed: a flush is done at the last close and all blocks
are invalidated.  The standard ``table full'' routines are called when
the file related tables fill up.  These routines no longer pass
\fBstruct chan *\fR pointers down to called routines, passing, instead,
the more universal \fBstruct file *\fR pointers from which the \fBchan\fR
pointers are easily derived.
.BP iget.c
Now uses the standard \fItablefull\fR routine.
.BP ioctl.c
The last argument to \fId_ioctl\fR routines when called is now always 0.
.BP locore.s
Has been extensively changed to accomodate the new configurable system,
and to handle multiple UNIBUS and MASSBUS adapters.  The code is now
written using macros and the C preprocessor, improving readability.
Complicated logic (such as the code to handle UNIBUS adapter errors)
has been migrated to C code.
.IP
MASSBUS and UNIBUS adapters are no longer initialized or mapped here;
this is the job of the configuration code in the system.
The locore code distinguishes, in handling UNIBUS interrupts, from
the machine being \fIcold\fR and not; when cold UNIBUS interrupts are
handled so as to be suitable for determined device vectoring via probing.
Device interrupts on the UNIBUS are now vectored through the code in
a file \fBubglue.s\fR produced by the configuration program.  To mask
as much as possible the differences between the different VAX processors,
the 11/780 uses the same \fBubglue.s\fR as the other processors which
directly vector UNIBUS interrupts.
.IP
Many more of the exceptional conditions
in the machine are caught now; only ``SBI alert'' and ``SBI fault'' remain
uncaught by UNIX.  The system control block is now defined in a file
\fBscb.s\fR so that some symbols derived from C language header files by
a program (and printed into a format suitable for inclusion in an assembly)
may be stuck in after the system control block and before the mainline
\fBlocore.s\fR.
.IP
The primitive routines \fIcopyseg\fR and \fIclearseg\fR are no longer
run with the IPL raised very high.
Further minor bugs have been fixed in the primitives, notably
\fIaddupc\fR (a bug which caused 1/8 of the profiling ticks to be lost),
and \fIkernacc\fR (a bug which allowed a strange command to a certain
program to crash the system).
.BP machdep.c
.br
Now sets up the error message buffer (in the last 1024 bytes of core)
and the system data structures (such as the file and process table)
at boot time.  Currently only the file system buffer cache is sized
at boot time, but all data structures are easily sized here.  The startup
routine also calls the routine \fIconfigure\fR to configure the system
for the current hardware, locating available devices.
.IP
The \fIsendsig\fR routine passes a code back when a SIGFPE or SIGILL arrives,
letting the signal handler determine which of the several conditions mapped
to these two signals actually occurred.  It uses the <frame.h> header file
rather than redefining it.
.IP
The routines which monitor memory errors are now driven by interrupts
(since the previous polling technique works only on 11/780).  Extensive
use of macros is made to make the various VAXen look similar.
Instead of printing the raw contents of the memory controller registers,
a array address and a syndrome is printed.  Multiple memory controllers
are supported.
.IP
The routines related to UNIBUS monitoring have been put with the rest of the
UNIBUS routines in \fB../dev/uba.c\fR.  The reboot interface has been
improved, adding an automatic crash dump to a dump device (normally
a disk aimed at the back end of a paging area).  The system no longer
``halts'' when you ask it to (since this can cause a reboot to occur);
rather it raises the IPL as high as it can and goes into a tight loop.
Routines have been added to handle machine checks and print out the
stack frame in a format which is readable by one who grok's what
the fields mean.
.BP main.c
Now establishes a red zone between the stack and \fIu.\fR area in process 0;
further processes also have red zones, protecting the \fIu.\fR from too-large
stacks.  The main routines also setup the super-blocks which are locked
into the file system buffer cache, and copy the name of the root file system
(/) into its super-block so that the name will be available if, e.g., the
root file system becomes full.
.BP malloc.c
Has been renamed \fBrmap.c\fR.
.BP nami.c
Now respects the notion of \fB..\fR in a directory which is a virtual root
directory after a \fIchroot\fR\|(2) call.
.BP prf.c
No longer implements the ascii in-core event tracing facility,
which proved to be too slow to
be useful; a binary facility replaces it, and is also conditionalized
on TRACE, but implemented in \fBvmmon.c\fR.
Implements the output of numbers non-recursively, since
the recursive method occasionally caused the kernel stacks to overflow.
Implements a new kernel routine \fIuprintf\fR which prints directly on a user's
terminal for informing him/her of situations such as file systems which
are full (because his/her program wrote to the file system when it was full.)
Implements a new format ``%b'' which takes two arguments, a number and
a second pattern.  The pattern specifies a base to print the number in,
and then a set of short strings separated by bit numbers (origin 1, escaped
in octal into the string in the C compiler).  The format prints the
symbolic names for the bits which are in the string and set in the number
within <>'s and separated by commas.  This is extensively used to produce
readable system error diagnostic messages on the console, decoding
the bits of device registers symbolically.
.IP
The routines \fIprdev\fR and \fIdeverr\fR, which printed diagnostics
which were difficult to interpreter, are deleted.  There are two new
routines: \fItablefull\fR which balks that a table is full, and
\fIharderr\fR which begins a message about a hard (unrecoverable)
error on a device.
.BP prim.c
Now maintains a count of free \fIclist\fR space.
The code here now runs at \fBspl5\fR rather than \fBspl6\fR since
there is no longer any need to block the clock.
.BP rdwri.c
Sees the change FASTVAX to not UNFAST.  Also always clears the set-user-id
bit when a file with the bit set is written on; previously this
was done only ``#if UCB''.  If you ``#define INSECURITY'' you get the
code the old way.
.BP scb.s
Is a new file defining the system control block (as described above).
.BP sig.c
Has a bug fixed which caused processes to occasionally stop when the
shell thought they were running.
Processes are now given signals immediately when they are sent if the
process is running.
.BP slp.c
A clumsiness which forced the swapout code to run with the IPL raised
has been fixed by adding a variable \fIwantin\fR with which \fIwakeup\fR
can communicate to the swapper that a swapped out process now wants
to return to memory.
The routine \fIsetpri\fR has been modified so that
processes which are over their declared (soft) memory size limitation
are assigned lower CPU priority when the system is very tight on memory.
.BP sys.c
No longer allows detached jobs to access /dev/tty; this was a security
glitch.
.BP sys1.c
Implements the ``#!'' executable shell script scheme.  No longer lets
executable files be read by users using \fIptrace\fR unless the user
has read access.
Operates \fIexec\fR much more efficiently by avoiding copying argument
lists unless the \fIexec\fR is going to succeed.
.BP sys2.c
The \fIopeni\fR routine passes both the FREAD and FWRITE flags to its
callees; this is needed by the magnetic tape open routines.
The \fImaknode\fR routine sticks the whole argument value in the ``rdev''
field of the inode.  This is used by the \fIbadblock\fR\|(8) program
to store block numbers corresponding to bad sectors on the disk in otherwise
apparently empty files.
.BP sys3.c
The \fImount\fR and \fIumount\fR calls have been changed to deal correctly
with buffer flushing and with simulateous access by other programs to
the file system block devices.  The \fImount\fR call also copies into the
super-block of the file system the name of the device on which the file
system is mounted (e.g. /usr).
.BP sys4.c
The \fIsyslock\fR routine has been moved here from \fBacct.c\fR.
The mechanisms for sending signals to all processes, which is used in
shutting down the system, has been changed so that the process which is
broadcasting the signal does not receive it itself.  This allows the
\fIhalt\fR and \fIshutdown\fR programs to be written in a straightforward way.
.BP trap.c
Prints out the \fBpc\fR when an unexpected trap occurs.
Handles AST's to implement profiling ticks and for rescheduling rather
than the (older style) use of reschedule interrupts.
Allows process reschedules after page faults.
.BP vmmon.c
Contains the internal routine \fBtrace1\fR which implements kernel
event tracing in a circular buffer.
.BP vmpage.c
Tracing code, which is normally not compiled in, has been added.
A extra case was added to an \fIif\fR statement to allow implementation
of the vlimit(LIM_MAXRSS) feature of the system, for limiting processes
which consume more than a process specific amount of physical memory.
A botch was fixed in the virtual memory pre-paging which put pre-paged
pages in the clock loop rather than at the end of the free list.
Code has been added to implement a additonal replacement algorithm
for processes which are declared sequential: when a hard page fault
occurs, the pages sequentially preceding the faulted page are returned
to the free list.
.BP vmproc.c
Contains a number of small changes related to AST processing.
.BP vmpt.c
Also contains changes for handling AST's as well as the initialization
of the red-zone separating the stack and \fBu.\fR area of newly created
processes.
A bug in translation buffer flushing which caused rare and mysterious
kernel crashes with the kernel stack not valid has been fixed.
.BP vmsched.c
Code has been added here which initializes the parameters of the clock
page replacement algorithm based on the size of the machine.  The \fIswapout\fR
routine has been changed so that it no longer runs entirely at a high
interrupt priority level (see \fBslp.c\fR above).  The algorithm for
the choice of processes to swap in and out and the hysteresis in the
swap algorithm has been adjusted to work reasonably in extreme conditions
when there are very large and or very few processes active in the system.
.BP vmsubr.c
Contains the \fIsetredzone\fR routine definition.
.BP vmsys.c
Contains the user interface to the kernel tracing routines.
Code has been added to \fIvadvise\fR to setup VA_SEQL.
.SH
Device support: sys/dev
.PP
The major change to the device subsystem is the support of multiple
MASSBUS and UNIBUS adapters, the support for multiple instances of each
particular controller, and the support of system configuration at
bootstrap time, investigating the interconnects, devices, and
controllers available on the machine.
These changes will be discussed in detail in the next section,
which describes how to change existing drivers to work in the new system
and gives pointers on style for writing new drivers.
.PP
Other changes in the device drivers affecting more than one driver:
.IP *
The input silos for DH-11's and DZ-11's are no longer serviced at clock IPL.
Rather the clock interrupt queues a software interrupt during to
service the silos.  This means that the device interrupt routines
are called from IPL 0x15, the IPL at which they normally interrupt.  Thus
it is no longer necessary to define \fBspl5\fR to be \fBspl6\fR (blocking
the clock) in routines which handle asynchronous line input/output.
.IP *
The internal interface to the line discipline routines has been changed
slightly by reordering parameters to make the arguments to the various
\fIioctl\fR interfaces more similar; in particular \fIttioctl\fR routine
call has been changed.  If you have locally written line disciplines
or asynchronous device drivers you should check the interfaces.
.IP *
The tty interface now provides full 8-bit output when the terminal is
in LLITOUT mode; this requires support from the \fIxx\fR\|param routines
in the device drivers (e.g. from \fIdhparam\fR and \fIdzparam\fR.)
.IP *
The UNIBUS adapter support routines have changed substantially, to allow
for queueing of requests when resources are short and for support of
multiple UNIBUS adapters.  The interface now also allows devices which
cannot function when other DMA is active on the UNIBUS to obtain
exclusive transient use of UNIBUS resources; this is needed to successfully
run RK07 disk controllers in the presence of other buffered data path DMA.
In addition, it is used by 6250bpi tape drives supported on the UNIBUS.
See the section on configuration and UNIBUS device drivers below
for more information.
.IP *
DEC standard bad sector forwarding is provided for all standard DEC
devices using the DEC formatters; the code which implements this is
easily ported to the storage module drivers in the system, and this
is planned soon.*
.FS
* The hard thing in providing bad sector handling for non-DEC drives
is providing a formatter which produces the bad block information and
flags the bad sectors appropriately.
.FE
.BP bio.c
The hashing of buffers has been changed to use the existing device
chain two way links.  This means that unhashing is much easier, saves
space, and uses the pointers which were otherwise little used.
The buffers are now kept on one of three lists when not busy: a list
of super-blocks which are locked in core, a list of good data blocks,
which is kept fifo and used to implement the LRU buffer cache, and a list of 
data blocks for which further usage is not anticipated; this is also
kept fifo.
.IP
Calls to some new tracing routines are conditionally included in \fBbio.c\fR;
we are using them to do some performance measurement.  The \fBd_tab\fR
field of the block device table has been changed to a \fBd_flags\fR field,
and that change is known here, where old field was checked before (to
see if it was non-zero).  Better messages are printed now when swap
space is exhausted, and a user is told on his/her terminal that a process
was killed before it started because there was no space.
A subroutine has been added to purge the blocks from a specific device
from the cache; this is used to fix some long standing buffer cache
flushing problems which prevented removable media from being used
reliably.
.BP bk.c
The definition of \fBspl5\fR as \fBspl6\fR has been removed from here.
The line discipline is included only if the specification
.DS
pseudo-device bk
.DE
is included in the system configuration.
The input silos on \fBdh\fR and \fBdz\fR devices are used only when
this line discipline is included in the system.
The comment about future implementation of 8-bit paths with this
discipline has been deleted, since there is no longer any intention of
doing this.
.BP conf.c
Has been moved to this directory from the directory \fB../conf\fR.
\fBThis file should be changed only if you are adding support for
a device not included on the standard distribution tape.\fR
.BP ct.c
Is a new driver, for a C/A/T phototypesetter interface.
.BP dh.c
No longer has to define \fBspl5\fR to be \fBspl6\fR.
Incorporates the DM-11 driver standardly.  A method is provided
for specifying that lines are to be operated even though the hardware
does not indicate that they are ready (using the flags word in the
configuration specification, see \fIdh\fR\|(4)).  A reasonable messages
is printed when a \fBdh\fR silo overflows, replacing the old style of
just printing a sequence of letter \fBo\fR's on the console.
.BP dhfdm.c
Has been incorporated into \fBdh.c\fR.
.BP dn.c
A driver for the DEC DN-11 autodialer interface.
.BP dsort.c
Has been rewritten to correct a bug which caused the elevators
to be sorted incorrectly.
.BP dz.c
No longer has to define \fBspl5\fR to be \fBspl5\fR.
Has been changed to allow lines to be specified as not properly wired
and brought up without the ready signals showing in the interface;
see \fIdz\fR\|(4) for details.  Prints reasonable diagnostics when
the input silo overflows.
.BP flp.c
Knows that there is no floppy on an 11/750.
.BP hp.c
Is now a sub-driver to \fBmba.c\fR, which probes nexus space for the MASSBUS
adaptors and device space on the MASSBUS's for disks, setting up the
driver for each device which is in the configuration.
A number of minor bugs and enhancements have been made to the driver:
The driver handles the new RM80 drive
and its SSE (skip-sector-error) facility for bad sector handling,
as well as the DEC standard bad block forwarding.
Due to the bad block forwarding, the last three tracks of each disk
are normally reserved to the system and available only through the
use of a special file system partition.
A further bug has been fixed in the initialization of the tables for RM05
sectoring.
The driver no longer (baroquely) turns on and off interrupts
on the MASSBUS adapter.  Basic dual-port drive handling code has
been added to the driver.
.IP
The remaining remarks apply to all three supported disk drivers:
the \fBhp\fR driver for MASSBUS disks, the \fBup\fR driver for
UNIBUS storage modules, and the \fBhk\fR driver for RK07's:
The drivers do
not SEARCH or SEEK if there is only one drive on the MASSBUS.  On a UNIBUS
no SEARCHing or SEEKing is done if one drive is on the controller.
The offset positions and recalibration of error recovery 
is now done with interrupts rather than by waiting for the operations
to complete.  This prevents the system from being tied up during the
many recoveries of a disk operation, and is necessary in any case
in at least one of the disk drivers (RK07).
The iostat numbers for each MASSBUS and UNIBUS drive are calculated
by the auto-configurator at boot time, not compiled into the drivers.
Much cleaner handling of errors is done: the drivers realize which
errors are not even potentially recoverable, handle drives spinning
up and down with readable diagnostics, and print reasonable, legible
error messages when hard errors and soft ecc's occur.
Each driver includes a low-level non-interrupt driver used to take
crash dumps at the end of a paging area on the device.
The drivers include a raw i/o buffer per drive so that raw operations
on separate devices can be overlapped (both seeks and transfers); previously
only one raw device operation could be pending per device type.
.BP ht.c
The tape drive is now a sub-drive of the MASSBUS driver.  The following
remarks apply to all supported tape drivers: \fBht\fR and \fBmt\fR
for MASSBUS
.	\"tapes, \fBts\fR for the UNIBUS ts-11, \fBtm\fR for the UNIBUS
.	\"TM-11 emulations, and \fBut\fR for UNIBUS TU45 emulations.
tapes, \fBts\fR for the UNIBUS ts-11, and \fBtm\fR for the UNIBUS
TM-11 emulations.
.IP
Each driver implements a set of tape ioctl operations on raw tapes providing
access to the functionality of the hardware such as skipping forward
and backward records and files and writing end-of-file marks on the tape.
Better error diagnostics are also given on tape errors.
Multiple tape controllers and transports are supported. 
A dump routine is provided with each driver for taking a
post-mortem crash dump on tape, although dumps are normally made
to the paging area on the disk.
.IP
With the exception of the \fBts\fP driver,
the drivers detect and reject
attempts to switch tape density while writing a tape.
.BP lp.c
Is a fully supported driver for one or more line printer interfaces.
It has been improved from the previous drivers (which were not supported)
to take a small fraction of the number of interrupts that the previous
drivers took.  The user-level code driving the printers has been arranged
to work on 1200 baud DECWRITER III terminals or true printers.
.BP mba.c
Has been rewritten.  Now allows mixing of disks and tapes on the same
and across multiple mba's, with the devices being driven from the routines
here calling routines defined in the individual device drivers.
.BP mem.c
Has been fixed to not allow any access to nexus space, even by the
super-users, since such access inevitably results in a machine check
and a system crash.
.BP mt.c
A driver for the DEC TU78 tape drive.
.BP mx?.c
A bug has been fixed which, caused by a missing call to \fIchdrain\fR
caused multiplexor files to become clogged under certain circumstances.
.BP rk.c
Is a new driver for RK07 disks.  It uses the same logic as the storage
module drive driver \fBup.c\fR whenever possible.  It also makes use
of the interlocking facilities of the UNIBUS device support because the
\fBrk\fR controller cannot tolerate concurrent UNIBUS dma when it is operating
due to a design flaw.
.BP swap.c
Now places only half of the first piece of the \fIswapmap\fR in the
\fIargmap\fR.
.BP swap??*.c
Are the files for different swap configurations.  Thus \fBswaphp.c\fR
defines the root and swap devices for a UNIX based on a \fBhp\fR disk.
The files such as \fBswaphphp.c\fR are for interleaved paging configurations,
placing the swapping and paging activity on two disk arms.  You can
make additional such files and include them in your configuration
files.
.BP tdump.c
Has been deleted, replaced by the dump routines in individual drivers.
.BP tm.c
Is a driver for UNIBUS tape drives on controllers such as the EMULEX TC-11.
It has the same functionality as \fBht\fR (see \fBht.c\fR above.)
.BP ts.c
Is a driver for the UNIBUS TS-11 tape drive.  It has full functionality
except the transport itself only supports 1600 bpi.
.BP tty.c
No longer raises its IPL to \fBspl6\fR internally to block the clock.
Has its internal interface to \fBioctl\fR entries changed slightly to
be globally consistent (see, e.g. \fIttioctl\fR).  The DIOC* ioctl
entries have been deleted since they are not used in any standard
UNIX line disciplines.
.BP ttynew.c
A bug is fixed which prevented echoing from occurring in raw mode.
The dec-compatible method of ^S/^Q processing needed to support VT-100s
in smooth scroll mode is implemented when the local mode ``decctlq''
is specified.
.BP ttyold.c
Implements ``decctlq'' mode.
.BP tu.c
A driver for the 11/750 TU58 console cassette interface.  \fBNote:
this driver provides reliable service only on a quiescent system.\fP
.BP uba.c
Has a much more structured interface.  All the basic routines for dealing
with the UNIBUS specify a UNIBUS adapter number to use, since there
are potentially several on a machine.  When requesting allocation
of UNIBUS map entries, the caller specifies whether he is willing
to block in the allocation routines waiting for resources to come
available.  If he is not, and there are no resources available, a value
of 0 is returned, and the caller must deal with this.  
The routine which frees UNIBUS resources now takes the address of the
variable describing the resources to be freed rather than the value
of this variable to eliminate a race condition (where the routine is
called, a UNIBUS interrupt occurs causing a UNIBUS reset, and the
resources are freed twice, causing a \fIpanic\fR\|).
.IP
The normal interface for DMA operation is now to pass a pointer to
a UNIBUS related structure to a routine \fIubago\fR, which allocates
UNIBUS resources.  If resources are not available, the structure
is queued on a request queue, and processed when resources are available.
When the requested resources are allocated, a driver specific \fIxxgo\fR
routine is called, and can stuff the device registers with the
address into which the operation is mapped and start the operation.
The use of this interface is described in the next section.
.IP
Finally, we note that the error handling code which was written
in assembly language is now written in C.
.BP uda.c
A driver for the UDA50 disk controller with RA80 Winchester
storage modules.
.BP up.c
The UNIBUS storage module disk driver has been fixed up in the same
way that the \fBhp\fR driver was, giving better error diagnostics
and using interrupts during error recovery, etc.  See \fBhp.c\fR
above for details.  The driver uses a feature of the EMULEX SC-21
to determine the size of the disks in use, so that it can adapt
to both 300M storage modules and the Fujitsu 160M drives which are
popular.  Other drive sizes can be added easily.
.	\".BP ut.c
.	\"A driver for the System Industries Model 9700 tape drive, emulating
.	\"a DEC TU45 on the UNIBUS.
.BP va.c
The \fBvarian\fR printer-plotter driver has been modified so that
it can support more than one device, probes the devices so they
can be placed on differrent UNIBUS'es, and prints an error diagnostic
when device errors are detected.
.BP vaxcpu.c
Is a new file which contains initializations of various CPU-type
dependent structures.
.BP vp.c
Has been modified to handle multiple devices, and adapted to the
auto-configuration code.
.SH
Configuration and UNIBUS device drivers
.PP
Someday this section will be a separate document.
This section explains how to interface an existing UNIX
device driver to the VAX system, especially to the UNIBUS
routines and the autoconfiguration code.
.PP
A PDP-11, UNIX/32V or 3BSD or 4.0BSD
driver on the VAX UNIBUS will need to be modified
to run under 4.1BSD.  There are three reasons why such a driver
will need to be changed:
.IP 1)
4.1bsd supports multiple UNIBUS adapters.
.IP 2)
4.1bsd supports system configuration at boot time.
.IP 3)
4.1bsd manages the UNIBUS resources and does not crash when
resources are not available; the resource allocation protocol must
be honored.  In addition, devices such as the RK07 which require
everyone else to get off the UNIBUS when they are running
need cooperation from other DMA devices if they are to work.
.PP
Each UNIBUS on a VAX has a set of resources:
.IP *
496 map registers which are used to convert from the 18 bit UNIBUS
addresses into the much larger VAX address space.
.IP *
Some number of buffered data paths (3 on an 11/750, 15 on an 11/780)
which are used by high speed devices to transfer
data using fewer bus cycles.
.LP
There is a structure of type \fBstruct uba_hd\fR in the system per UNIBUS 
adapter used to manage these resources.  This structure also contains
a linked list where devices waiting for resources to complete DMA UNIBUS
activity have requests waiting.
.PP
There are three central structures in the writing of drivers for UNIBUS
controllers; devices which do not do DMA i/o can often use only two
of these structures.  The structures are \fBstruct uba_ctlr\fR, the
UNIBUS controller structure, \fBstruct uba_device\fR the UNIBUS
device structure, and \fBstruct uba_driver\fR, the UNIBUS driver structure.
The \fBuba_ctlr\fR and \fBuba_device\fR structures are in
one-to-one correspondence with the definitions of controllers and
devices in the system configuration.
Each driver has a \fBstruct uba_driver\fR structure specifying an internal
interface to the rest of the system.
.PP
Thus a specification
.DS
controller sc0 at uba0 csr 0176700 vector upintr
.DE
would cause a \fBstruct uba_ctlr\fR to be declared and initialized in
the file \fBioconf.c\fR for the system configured from this description.
Similarly specifying
.DS
disk up0 at sc0 drive 0
.DE
would declare a related \fBuba_device\fR in the same file.
The \fBup.c\fR driver which implements this driver specifies in
its declarations:
.DS
int     upprobe(), upslave(), upattach(), updgo(), upintr();
struct  uba_ctlr *upminfo[NSC];
struct  uba_device *updinfo[NUP];
u_short upstd[] = { 0776700, 0774400, 0776300, 0 };
struct  uba_driver scdriver =
    { upprobe, upslave, upattach, updgo, upstd, "up", updinfo, "sc", upminfo };
.DE
initializing the \fBuba_driver\fR structure.
The driver will support some number of controllers named \fBsc0\fR, \fBsc1\fR,
etc, and some number of drives named \fBup0\fR, \fBup1\fR, etc. where the
drives may be on any of the controllers (that is there is a single
linear name space for devices, separate from the controllers.)
.PP
We now explain the fields in the various structures.  It may help
to look at a copy of \fBh/ubareg.h\fR, \fBh/ubavar.h\fR and drivers
such as \fBup.c\fR and \fBdz.c\fR while reading the descriptions of
the various structure fields.
.SH
uba_driver structure
.PP
One of these structures exists per driver.  It is initialized in
the driver and contains functions used by the configuration program
and by the UNIBUS resource routines.  The fields of the structure are:
.BP ud_probe
A routine which is given a \fBcaddr_t\fR address as argument and
should cause an interrupt on the device whose control-status register
is at that address in virtual memory.  It may be the case that the
device does not exist, so the probe routine should use delays (via
the DELAY(n) macro which delays for \fIn\fR microseconds) rather than
waiting for specific events to occur.  The routine must \fBnot\fR
declare its argument as a \fBregister\fR parameter, but \fBmust\fR declare
.DS
\fBregister int br, cvec;\fR
.DE
as local variables.  At boot time the system takes special measures
that these variables are ``value-result'' parameters.  The \fBbr\fR
is the IPL of the device when it interrupts, and the \fBcvec\fR
is the interrupt vector address on the UNIBUS.  These registers
are actually filled in in the interrupt handler when an interrupt occurs.
.IP
As an example, here is the \fBup.c\fR
probe routine:
.DS
upprobe(reg)
        caddr_t reg;
{
        register int br, cvec;

#ifdef lint     
        br = 0; cvec = br; br = cvec;
#endif
        ((struct updevice *)reg)->upcs1 = UP_IE|UP_RDY;
        DELAY(10);
        ((struct updevice *)reg)->upcs1 = 0;
        return (1);
}
.DE
The definitions for \fIlint\fR serve to indicate to it that the
\fBbr\fR and \fBcvec\fR variables are value-result.  The statements
here interrupt enable the device and write the ready bit UP_RDY.
The 10 microsecond delay insures that the interrupt enable will
not be cancelled before the interrupt can be posted.  The return of
``1'' here indicates that the probe routine is satisfied that the device
is present.  A probe routine may use the function ``badaddr'' to see
if certain other addresses are accessible on the UNIBUS (without generating
a machine check), or look at the contents of locations where certain
registers should be.  If the registers contents are not acceptable or
the addresses don't respond, the probe routine can return 0 and the
device will not be considered to be there.
.IP
One other thing to note is that the action of different VAXen when illegal
addresses are accessed on the UNIBUS may differ.  Some of the machines
may generate machine checks and some may cause UNIBUS errors.  Such
considerations are handled by the configuration program and the driver
writer need not be concerned with them.
.IP
It is also possible to write a very simple probe routine for a one-of-a-kind
device if probing is difficult or impossible.  Such a routine would include
statements of the form:
.DS
br = 0x15;
cvec = 0200;
.DE
for instance, to declare that the device ran at UNIBUS br5 and interrupted
through vector 0200 on the UNIBUS.  The current TS-11 driver does 
something similar to this because the device is so difficult to force
an interrupt on that it hardly seems worthwhile.  (Besides, TS-11's are
usually present on small 11/750's which have only one UNIBUS, and TS-11's
can have only exactly one transport per-controller so little probing is
needed.)
.BP ud_slave
This routine is called with a \fBuba_device\fR structure (yet to
be described) and the address of the device controller.  It should
determine whether a particular slave device of a controller is
present, returning 1 if it is and 0 if it is not.
As an example here is the slave routine for \fBup.c\fR.
.DS
upslave(ui, reg)
        struct uba_device *ui;
        caddr_t reg;
{
        register struct updevice *upaddr = (struct updevice *)reg;

        upaddr->upcs1 = 0;              /* conservative */
        upaddr->upcs2 = ui->ui_slave;
        if (upaddr->upcs2&UPCS2_NED) {
                upaddr->upcs1 = UP_DCLR|UP_GO;
                return (0);
        }
        return (1);
}
.DE
Here the code fetches the slave (disk unit) number from the \fBui_slave\fR
field of the \fBuba_device\fR structure, and sees if the controller
responds that that is a non-existant driver (NED).  If the drive
a drive clear is issued to clean the state of the controller, and 0 is
returned indicating that the slave is not there.  Otherwise a 1 is returned.
.BP ud_attach
The attach routine is called after the autoconfigure code and the driver concur
that a peripheral exists attached to a controller.  This is the routine
where internal driver state about the peripheral can be initialized.
Here is the \fIattach\fR routine from the \fBup.c\fR driver:
.ID
.nf
upattach(ui)
        register struct uba_device *ui;
{
        register struct updevice *upaddr;

        if (upwstart == 0) {
                timeout(upwatch, (caddr_t)0, hz);
                upwstart++;
        }
        if (ui->ui_dk >= 0)
                dk_mspw[ui->ui_dk] = .0000020345;
        upip[ui->ui_ctlr][ui->ui_slave] = ui;
        up_softc[ui->ui_ctlr].sc_ndrive++;
        upaddr = (struct updevice *)ui->ui_addr;
        upaddr->upcs1 = 0;
        upaddr->upcs2 = ui->ui_slave;
        upaddr->uphr = UPHR_MAXTRAK;
        if (upaddr->uphr == 9)
                ui->ui_type = 1;                /* fujitsu hack */
        upaddr->upcs2 = UPCS2_CLR;
}
.DE
The attach routine here performs a number of functions.  The first
time any drive is attached to the controller it starts the timeout
routine which watches the disk drives to make sure that interrupts
aren't lost.  It also initializes, for devices which have been assigned
\fIiostat\fR numbers (when ui->ui_dk >= 0), the transfer rate of the
device in the array \fBdk_mspw\fR, the fraction of a second it takes
to transfer 16 bit word.  It then initializes an inverting pointer
in the array \fBupip\fR which will be used later to determine, for a
particular \fBup\fR controller and slave number, the corresponding
\fBuba_device\fR.  It increments the count of the number of devices
on this controller, so that search commands can later be avoided
if the count is exactly 1.  It then uses a hardware feature of the
EMULEX SC-21 to ask if the number of tracks on the device is 9.  If
it is, then the driver assumes that the type is ``1'', which corresponds
to a FUJITSU 160M drive.  The alternative is the only other currently
supported device, a 300 Megabyte CDC or AMPEX drive, which has \fBui_type\fR
0.  Note that if the controller is not an SC-21 then attempting to find
out the maximum track in the device will yield an error, and a 300
Megabyte device will be assumed.  In any case, any errors resulting from
the attempt to type the drive are cleared by a controller clear before
the routine returns.
.BP ud_dgo
Is the routine which is called by the UNIBUS resource management
routines when an operation is ready to be started (because the required
resources have been allocated).  The routine in \fBup.c\fR is:
.DS
updgo(um)
        struct uba_ctlr *um;
{
        register struct updevice *upaddr = (struct updevice *)um->um_addr;

        upaddr->upba = um->um_ubinfo;
        upaddr->upcs1 = um->um_cmd|((um->um_ubinfo>>8)&0x300);
}
.DE
This routine uses the field \fBum_ubinfo\fR of the \fBuba_ctlr\fR
structure which is where the UNIBUS routines store the UNIBUS
map allocation information.  In particluar, the low 18 bits of this
word give the UNIBUS address assigned to the transfer.  The assignment
to \fIupba\fR in the go routine places the low 16 bits of the UNIBUS
address in the disk UNIBUS address register.  The next assignment
places the disk operation command and the extended (high 2) address
bits in the device control-status register, starting the i/o operation.
The field \fBum_cmd\fR was initialized with the command to be stuffed
here in the driver code itself before the call to the \fBubago\fR
routine which eventually resulted in the call to \fBupdgo\fR.
.BP ud_addr
Are the conventional addresses for the device control registers in
UNIBUS space.  This information is not used by the system in this
release, but may be used in future releases to look for instances of
the device supported by the driver.  In the current system, the configuration
file specifies the control-status register addresses of all configured devices.
.BP ud_dname
Is the name of a \fIdevice\fR supported by this controller; thus the
disks on a SC-21 controller are called \fBup0\fR, \fBup1\fR, etc.
That is because this field contains \fBup\fR.
.BP ud_dinfo
Is an array of back pointers to the \fBuba_device\fR structures for
each device attached to the controller.  Each driver defines a set of
controllers and a set of devices.  The device address space is always
one-dimensional, so that the presence of extra controllers may be
masked away (e.g. by pattern matching) to take advantage of hardware
redundancy.  This field is filled in by the configuration program,
and used by the driver.
.BP ud_mname
The name of a controller, e.g. \fBsc\fR for the \fBup.c\fR driver.
The first SC-21 is called \fBsc0\fR, etc.
.BP ud_minfo
The backpointer array to the structures for the controllers.
.BP ud_xclu
If non-zero specifies that the controller requires exclusive
use of the UNIBUS when it is running.  This is non-zero currently
only for the RK611 controller for the RK07 disks to map around a hardware
problem.  It could also be used if 6250bpi tape drives are to be used
on the UNIBUS to insure that they get the bandwidth that they need
(basically the whole bus).
.SH
uba_ctlr structure
.PP
One of these structures exists per-controller.
The fields link the controller to its UNIBUS adaptor and contain the
state information about the devices on the controller.  The fields are:
.BP um_driver
A pointer to the \fBstruct uba_device\fR for this driver, which has
fields as defined above.
.BP um_ctlr
The controller number for this controller, e.g. the 0 in \fBsc0\fR.
.BP um_alive
Set to 1 if the controller is considered alive; currently, always set
for any structure encountered during normal operation.  That is, the
driver will have a handle on a \fBuba_ctlr\fR structure only if the
configuration routines set this field to a 1 and entered it into the
driver tables.
.BP um_intr
The interrupt vector routines for this device.  These are generated
by the \fIconfig\fR\|(8) program and this field is initialized in the
\fBioconf.c\fR file.
.BP um_hd
A back-pointer to the UNIBUS adapter to which this controller is attached.
.BP um_cmd
A place for the driver to store the command which is to be given to
the device before calling the routine \fIubago\fR with the devices
\fBuba_device\fR structure.  This information is then retrieved when the
device go routine is called and stuffed in the device control status register
to start the i/o operation.
.BP um_ubinfo
Information about the UNIBUS resources allocated to the device.  This is
normally only used in device driver go routine (as \fBupdgo\fR above)
and occasionally in exceptional condition handling such as ECC correction.
.BP um_tab
This buffer structure is a place where the driver hangs the device structures
which are ready to transfer.  Each driver allocates a buf structure for each
device (e.g. \fBupdtab\fR in the \fBup.c\fR driver) for this purpose.
You can think of this structure as a device-control-block, and the
buf structures linked to it as the unit-control-blocks.
The code for dealing with this structure is stylized; see the \fBrk.c\fR
or \fBup.c\fR driver for the details.  If the \fBubago\fR routine
is to be used, the structure attached to this \fBbuf\fR structure
must be:
.RS
.IP *
A chain of \fBbuf\fR structures for each waiting device on this controller.
.IP *
On each waiting \fBbuf\fR structure another \fBbuf\fR structure which is
the one containing the parameters of the i/o operation.
.RE
.SH
uba_device structure
.PP
One of these structure exists for each device attached to a UNIBUS
controller.  Devices which are not attached to controllers or which
perform no buffered data path
DMA i/o may have only a device structure.  Thus \fBdz\fR
and \fBdh\fR devices have only \fBuba_device\fR structures.
The fields are:
.BP ui_driver
A pointer to the \fBstruct uba_driver\fR structure for this device type.
.BP ui_unit
The unit number of this device, e.g. 0 in \fBup0\fR, or 1 in \fBdh1\fR.
.BP ui_ctlr
The number of the controller on which this device is attached, or \-1
if this device is not on a controller.
.BP ui_ubanum
The number of the UNIBUS on which this device is attached.
.BP ui_slave
The slave number of this device on the controller which it is attached to,
or \-1 if the device is not a slave.  Thus a disk which was unit 2 on
a SC-21 would have \fBui_slave\fR 2; it might or might not be \fBup2\fR,
that depends on the system configuration specification.
.BP ui_intr
The interrupt vector entries for this device, copied into the UNIBUS
interrupt vector at boot time.  The values of these fields are filled
in by the \fBconfig\fR\|(8) program to small code segments which it
generates in the file \fBubglue.s\fR.
.BP ui_addr
The control-status register address of this device.
.BP ui_dk
The iostat number assigned to this device.  Numbers are assigned to
disks only, and are small positive integers which index the various
\fBdk_*\fR arrays in <sys/dk.h>.
.BP ui_flags
The optional ``\fBflags \fR\fIxxx\fR'' parameter from the configuration
specification was copied to this field, to be interpreted by the driver.
If \fBflags\fR was not specified, then this field will contain a 0.
.BP ui_alive
The device is really there.  Presently set to 1 when a device is
determined to be alive, and left 1.
.BP ui_type
The device type, to be used by the driver internally.  Thus the \fBup.c\fR
driver uses a \fBui_type\fR of 0 to mean a 300 Megabyte drive and a type
of 1 to mean a 160 Megabyte FUJITSU drive.
.BP ui_physaddr
The physical memory address of the device control-status register.
This is used in the device dump routines typically.
.BP ui_mi
A \fBstruct uba_ctlr\fR pointer to the controller (if any) on which
this device resides.
.BP ui_hd
A \fBstruct uba_hd\fR pointer to the UNIBUS on which this device resides.
.SH
Changing drivers
.PP
If you driver does not do buffered data path DMA, conversion
to the new system should be straightforward; if it uses
buffered data paths more work will be required, but the
task is really mostly cosmetic.
.PP
In any case, first add a line to the file \fBconf/files\fR of the form
.DS
dev/zz.c	optional zz device-driver
.DE
so that your driver will be included when you
specify it in a configuration.
Change the \fBdev/conf.c\fR file to include a block or character
device entry for your device.  Note that the block device entries
now include a \fBd_dump\fR entry; if you are a block device but
don't have a dump entry point, just make one in your driver that
returns the value ENODEV.
.PP
Then build a system configuration including your driver so that
you have a compilation environment for your driver.  You will
have to add a \fBstruct uba_driver\fR declaration for your driver,
and change its calls to UNIBUS routines to correspond to these
routines in the new system.  Trouble spots will show up here.
In particular, notice that you must specify flags to \fBuballoc\fR
if you call it:
.BP NEEDBDP
if you need a buffered data path
.BP CANTWAIT
if you are calling (potentially) from interrupt level
.LP
You may discover that your driver ``cantwait'' but that you are calling
from interrupt level.  This botch existed in most previous VAX UNIX
drivers, since there were no mechanisms for dealing with this.
We will describe some options shortly.
.PP
First, suppose your driver doesn't do buffered data path dma.
What else is there for you to do?  Very little really.
You should change your driver to print messages on the console
in the format now used by all device drivers; see section 4 of the
revised programmers manual for details.
To make more certain that your driver is ready for the new system
environment, look at some of the simple existing drivers
and mimic the style to create the portions of the driver which
are needed to interface with the configuration part of the system.
Useful drivers to look at may be:
.BP ct.c
Very simple drive which does programmed i/o to C/A/T phototypesetter.
.BP dh.c
Communications line driver which uses non-buffered UNIBUS dma
for output.
.BP dz.c
Communications line driver which does programmed i/o.
.PP
Basically all you have to do is write a \fBud_probe\fR and a \fBud_attach\fR
routine for the controller.  It suffices to have a \fBud_probe\fR routine
which just initializes \fBbr\fR and \fBcvec\fR, and a \fBud_attach\fR
routine which does nothing.
Making the device fully configurable requires, of course, more work,
but is worth it if you expect the device to be in common usage
and want to share it with others.
.PP
If you managed to create all the needed hooks, then make sure you include
the necessary header files; the ones included by \fBct.c\fR are nearly
minimal.  Order is important here, don't be suprised at undefined structure
complaints if you order the includes wrongly.
Finally if you get the device configured in, you can try bootstrapping
and see if configuration messages print out about your device.
It is a good idea to have some messages in the probe routine so that
you can see that you are getting called and what is going on.
If you do not get called, then you probably have the control-status
register address wrong in your system configuration.  The autoconfigure
code notices that the device doesn't exist in this case and you will never
get called.
.PP
Assuming that your probe routine works and you manage
to generate an interrupt, then you are basically back to where you
would have been under older versions of UNIX.
Just be sure to use the \fBui_ctlr\fR field of the \fBuba_device\fR
structures to address the device; compiling in funny constants
will make your driver only work on the CPU type you have (780 or 750).
.PP
Other bad things that might happen while you are setting up the configuration
stuff:
.IP *
You get ``nexus zero vector'' errors from the system.  This will happen
if you cause a device to interrupt, but take away the interrupt enable
so fast that the UNIBUS adapter cancels the interrupt and confuses
the processor.  The best thing to do it to put a modest delay in the
probe code between the instructions which should cause and interrupt and
the clearing of the interrupt enable.  (You should clear interrupt
enable before you leave the probe routine so the device doesn't interrupt
more and confuse the system while it is configuring other devices.)
.IP *
The device refuses to interrupt or interrupts with a ``zero vector''.
This typically indicates a problem with the hardware or, for devices
which emulate other devices, that the emulation is incomplete.  Devices
may fail to present interrupt vectors because they have configuration
switches set wrong, or because they are being accessed in inappropriate ways.
Incomplete emulation can cause ``maintenance mode'' features to not work
properly, and these features are often needed to force device interrupts.
.SH
Adapting devices which do buffered data path dma
.PP
These devices fall into two categories: those which are controllers
to which devices are attached, and those which are just single devices.
The interface for the former is very stylized and we recommend that
you simply mimic one of the existing tape or disk drivers in adapting
to the system.  You will find that the existing tape and disk drivers
are all \fBvery\fR similar; this is deliberate so that it isn't
necessary to rewrite the whole driver for each device, since the available
devices are typically very similar.
.PP
Other devices which do buffered data path DMA can be adapted to the
new system in one of two ways:
.IP *
They can do their own data path allocation, calling the UNIBUS
allocation routines from the ``top-half'' (non-interrupt) code,
sleeping in the UNIBUS code when resources are not available.
See for an example the code in the \fBvp.c\fR driver.
.IP *
They can set up a two-level structure like the tape and disk drivers
do, and call the \fIubago\fR routine and use the \fBud_dgo\fR interface
to start DMA operations.
See for an example the code in the \fBup.c\fR driver.
.PP
Either way works acceptably well; the second (\fIubago\fR\|) interface
is preferable because it does not force a context switch per i/o operation
(to the routine driving the i/o from the ``top-half'').
.PP
If you have questions about converting drivers, feel free to call us
and ask or to send us mail.  We hope (eventually) to write a more
complete paper for driver writers, but don't have the manpower to do this
just now.