vm: fix potential null deref

[minix.git] / man / man8 / config.8

.TH CONFIG 8
.SH NAME
config \- configuring MINIX 3 tasks and servers
.SH DESCRIPTION
.de SP
.if t .sp 0.4
.if n .sp
..
MINIX 3 has a number of configuration files containing parameters that can
be changed to enable or disable a device driver, to change the number of
times a resource can be used, or to tune the performance of the system.
We will name the file that contains the parameter, the name of the
parameter, and the values it can be set to.  Some comments are prefixed by
"8086" for MINIX 3 running in 16-bit real mode, "286" for 16-bit protected
mode, and "386" for 32-bit protected mode.
Configuration file names can be
.RI < file.h >
for a file in
.BR /usr/include/ ,
or a simple file name for a file in
.BR /usr/src/ .
.PP
There may be several definitions for a parameter with only one that is
active.  Which one this is is easy to find if you know that
.B "(\s-2CPU\s+2\ ==\ \s-2INTEL\s+2)"
is true, and
.SB _WORD_SIZE
equals
.B 2
in 16-bit mode, and
.B 4
in 32-bit mode.
.PP
.ti 2m
.RB < minix/config.h >
.br
This is the main configuration file for the MINIX 3.  It contains lots of
boolean variables to enable or disable drivers and a number of parameters
that specify the sizes of system data structures:
.TP
.SB NR_PROCS
The number of slots in the process table, and thus the maximum number of
processes that can be run concurrently.  Should be increased from the
default
.B 32
if networking is enabled (add
.B 8
for deamons), and if more users are using the system (add
.B 4
for each active session).  There are a lot of
loops in the kernel scanning the process table, so setting
.SB NR_PROCS
too high will slow things down a little bit, so don't overdo it.
.TP
.SB NR_BUFS
The number of disk buffers in the file system server.  It is used to keep
frequently used disk blocks in memory.
.BR 8086 " & " 286 :
The default is
.BR 40 ,
and that's about as high as it can be set.
.BR 386 :
The default is
.BR 80 ,
which is best increased to
.B 1024
if you can spare the memory.  More will help, but the effect won't be as
pronounced as
.B 1024
is more than enough to contain the working set of one active user.
.TP
.SB NR_CTRLRS
Number of tasks used for disk or tape controllers.  By default 2, maximum 4.
You need a controller task for each device class to be handled through a
.BI /dev/c n "*"
set of devices.
.TP
.SB ENABLE_CACHE2
If set to 1 allows the RAM disk to be used as a second level file system
cache.  Any block that is evicted from the normal cache is both written to
disk (if dirty), and copied to the second level cache.  If it is needed
again then the block is reloaded from the RAM disk if it is still there.
.BR 8086 :
Forget it, you don't have any memory for it.
.BR 286 :
Turn it on and set the boot environment variable
.B ramsize
to
.B 512
if you have the memory.  That's enough to contain the working set of
one active user, and is also the maximum FS can handle.
.BR 386 :
The installation scripts sets
.B ramsize
to
.B 1024
if there is enough memory.  Your first point of call is to compile a
new kernel with
.SB ENABLE_CACHE2
off,
.SB NR_BUFS
set to a large value, and
.B ramsize
set back to zero.  A normal block cache works much better than a two level
arrangement.
.TP
.SB ENABLE_AT_WINI
Enables the AT or IDE disk driver.  (The IDE interface grew out of the old
AT disk interface.)  Any run of the mill PC needs this driver.  You need to
assign a driver like this one to a controller task using one of the
.BI c n
boot variables.  See
.BR boot (8).
.TP
.SB ENABLE_BIOS_WINI
Enables the BIOS disk driver.  The BIOS driver uses the system BIOS to read
or write disk blocks.
.BR 8086 :
The preferred disk driver for XT class machines.
.BR 286 " & " 386 :
Use a native driver if possible to avoid switching back to real mode to make
BIOS calls.  Especially on the 286 this is a painful affair.
.TP
.SB ENABLE_ESDI_WINI
Enables the ESDI disk driver.  Some PS/2 models have this disk.
.TP
.SB ENABLE_XT_WINI
Enables the XT disk driver.  Useful for early IBM/AT machines that have XT
disks.  In real mode it is best to use the BIOS driver.
.TP
.SB ENABLE_AHA1540_SCSI
Enables the Adaptec 1540 series SCSI driver.
.TP
.SB ENABLE_DOSFILE
Enable the "DOS file as disk" driver that is used when MINIX 3 is run from
MS-DOS to access a large file as a disk.
.TP
.SB ENABLE_FATFILE
Enable the "FAT file as disk" driver that interprets a FAT file system
to find a large file to use as a disk.  This driver combined with a fast
native MINIX 3 disk driver is a better choice then the previous driver.  (And
it works when MINIX 3 is not started from MS-DOS.)  This is the last driver
that needs to be assigned to a controller task.
.TP
.SB ENABLE_SB16
Enable the Soundblaster-16 audio driver.
.TP
.SB ENABLE_PRINTER
Enable the Printer driver.
.TP
.SB DMA_SECTORS
The size of the DMA buffer for drivers that use DMA or other drivers that
can only do I/O to a single chunk of memory.  (BIOS, ESDI, XT, DOSFILE.)
Choose a number between
.B 1
and
.B 128
for the sector size of this buffer.  The memory cost is twice this amount,
because of trouble getting it aligned in memory properly.  A value of
.B 16
is the minimum to work well, choose
.B 64
if you have enough memory.
.TP
.SB NR_CONSOLES
Number of virtual consoles.  By default
.BR 2 ,
so you can have two login sessions that can be switched to by ALT-F1,
ALT-F2 or ALT-left/rightarrow.  If you have an EGA screen then you can
specify up to
.B 4
virtual consoles, for VGA you can have
.BR 8 .
It is best to choose one less to leave some video memory to keep text
scrolling fast.  You really should read
.BR console (4)
on this.  Note also the
.B console
boot variable, you can use it to put more characters on the screen, at
the cost of video memory.
.TP
.SB ENABLE_DP8390
Master switch to enable the network drivers.  They are required by the
network server,
.BR inet .
See
.BR boot (8)
for information on configuring network support.
.TP
.SB ENABLE_WDETH
Enable code for the WD8003 and WD8013 cards in the network driver.
.TP
.SB ENABLE_NE2000
Enable code for the NE1000 and NE2000 cards.
.TP
.SB ENABLE_3C503
Enable code for the 3Com Etherlink II (3C503).
.TP
.SB NR_PTYS
Number of pseudo terminals supported, by default
.BR 0 ,
which disables the driver.  Pseudo terminals are used for incoming network
logins by telnet or rlogin.  One pty is needed per session.
.TP
.SB NR_RS_LINES
Number of RS-232 lines supported.  By default
.B 2
for a normal kernel, but
.B 0
for a tiny kernel used for XT installation.  You can save a bit of memory by
setting this parameter to zero if you don't need serial lines.
.PP
.ti 2m
.BR fs/const.h
.br
This file contains most of the parameters used by the file system code.
Most of these cannot be changed, with the exception of these four:
.TP
.SB NR_FILPS
Maximum number of open file descriptors for all processes combined.  A "File
table overflow" error might indicate that this number must be increased.
.TP
.SB NR_INODES
Maximum number of in-use files for all processes combined.  Like above a
"File table overflow" error may also indicate that this number should be
increased.  In cases like these one usually doubles both parameters.  (If
one table runs out then the other one is likely to run out also anyway.)
.TP
.SB NR_SUPERS
Number of file systems that can be mounted.  Again a "file table overflow"
error is given if this table is full, but it will be produced by the
.B mount
command, so you know what's wrong in this case.
.TP
.SB NR_LOCKS
Number of active file locks by
.BR fcntl (2).
These locks are often used by programs that update a shared file, like mail
programs do with mail boxes.  A "no locks available" error indicates that
this table has run out.
.PP
.ti 2m
.B kernel/bios_wini.c
.ti 2m
.B kernel/dosfile.c
.ti 2m
.B kernel/fatfile.c
.br
The number of disks each of these drivers can handle is specified by:
.TP
.B MAX_DRIVES
This parameter is set to
.B 4
for the BIOS and "DOS file" drivers, and to
.B 2
for the "FAT file" driver.  It can be set as high as you need to allow for
more disks, or files as disks.  (The "FAT" driver needs quite some memory per
disk, which is why it by default only allows 2 disks.)  You will need to run
.BR MAKEDEV (8)
to create the extra disk devices in
.BR /dev/ .
.PP
.ti 2m
.B inet/inet_config.h
.br
The maximum number of TCP/IP networks is:
.TP
.B IP_PORT_MAX
Sets the maximum number of networks that can be defined in
.BR /etc/inet.conf .
.BR 8086 ,
.BR 286 :
By default 2.
.BR 386 :
By default 4.
.PP
.ti 2m
.B inet/buf.c
.br
The number of 512 byte buffers allocated for data within the TCP/IP server is:
.TP
.B BUF512_NR
These buffers are a shared resource used by the server for any data it wants
to play with.  For incoming data this number of buffers determines the time
packets are kept around, with each new packet evicting an old packet.  It's
no big deal if packets get lost before a user process reads them, packets
get lost all the time.  The only real problem is outgoing TCP data.  The
default setting for
.SB BUF512_NR
allows up to four backlogged TCP streams, i.e. when data is output faster
then it is read.  If more buffers are needed then one of the TCP connections
is shut down.  When this happens you will see a "not enough buffers left"
error.  This could happen for instance if a MINIX 3 web server is assaulted by
a browser that likes to open several connections to the server
simultaneously.  The fix is to increase
.SB BUF512_NR
to allow more slow outgoing TCP streams.
.BR 86 :
The default of
.B 32
buffers can be increased up to
.BR 64 .
(The "TCP window size" has been limited in 16-bit mode to keep the buffer
use by TCP down.)
.BR 386 :
The default of
.B 128
can be increased to any value you like, but
.B 512
seems to be more than enough.  Minix-vmd uses 512 by default, and it seems
happy that way.
.SH "SEE ALSO"
.BR controller (4),
.BR usage (8),
.BR boot (8),
.BR MAKEDEV (8).
.SH NOTES
Associated with drivers there are device files to access the devices
controlled by the drivers that may have to be created.  Let's simplify this
sentence:  Type
.BR "ls /dev" ,
note that there are only
.B c0*
and
.B c1*
devices, and only for two disks each.  Some devices, like the audio devices,
are not even present.  So if you enable a driver, or increase some limits, you
also need to use
.BR MAKEDEV (8)
in
.B /dev
to allow programs to talk to the drivers.
.SH AUTHOR
Kees J. Bot (kjb@cs.vu.nl)