Subject: Linux Frequently Asked Questions 4/6 [monthly posted]
From: [email-masked]
Date: Thu, 10 Jun 1993 13:16:49 GMT
Newsgroups: comp.os.linux,comp.os.linux.announce,comp.answers,news.answers

Archive-name: linux-faq/part4

Last-Modified: 93/06/11
Version: 1.19

*********************************************************
*							*
*   Answers to Frequently asked questions about Linux   *
*							*
*********************************************************

This post contains Part 4 of the Linux FAQ (6 parts).
It must be read *after* the 3 first parts. 

===================================8<====>8============================
CONTENTS (of this part)

	VIII. 	FEATURES 			(part4)
	IX. 	GCC MISC INFORMATION		(part4)
	X.	SCSI SPECIAL			(part4)

===================================8<====>8============================

VIII. FEATURES 
==============

VIII.01)  I've read that linux has virtual consoles, what must I do to
get them?

ANSWER: Yes there are, you can access them with the left <alt>-key
together with <Fn>-key. With the Linux Images distribution, 4 consoles
are available, getty runs on them.  
Notice that they are NOT accessible when running X (contrary to some
commercial unices).

VIII.02)  When Linux boots, I get the following message "8 virtual
consoles"; how can I acess to the 5-8 vc's ?

ANSWER: If you want the getty to run on the 5-8, you should add the
corresponding entries in /etc/inittab. You can also just run sh on
them by using the doshell soft.
And then in either case, the ALT-F[5-8] will access the corresponding
vc.  

VIII.03)  What kind of shell is /bin/sh ?

ANSWER: It's the Bourne Again Shell, bash-1.12.3 and 
compilation was straightforward, just "make" 
that's all or nearly. 
BTW There does exist different shells for Linux, these are:
bash, rc, zsh, tcsh and pdksh (a korn shell).

VIII.04)  Does there exist a man page for **** ?

ANSWER: Download man.tar.Z from your favorite linux ftp site, there is
most of the fileutils man page -- either **** or g****, example there
is nothing on ld, but there is for gld :) --, check the whatis
database provided. The files in the cat1 dir are pre-formatted man
pages that the man program can use. Quite recently the man pages for
section 2 have been written (thanks Drew) and can be found, at least
at tsx-11 in /pub/linux/docs/man/man2.tar.Z 

Also manpages are in the SLS on the b? disks.

BTW there is nroff and groff for Linux. Cawf 2.0 works just
fine for simple man pages, and a partial ms support too. 

Moreover Michael Johnson is the coordinator for man pages under Linux,
he is looking for volunteers, so contact the DOC Channel.

VIII.05)  Is there a simple man package (groff is too big):

ANSWER: "Cawf -man" also "fm -m" (Al Clark) tsx-11 in
	 /pub/linux/binaries/usr.bin/fm.tar.Z 

VIII.06)  What are the editors available in linux?

ANSWER: Right now there are uemacs-3.11, elvis-1.4 (1.5). 
Gnu Emacs is there, read the section devoted to it in the 5th part of
this FAQ. Also the port of mg (micro gnu) has been done and can be
found at least at athos.rutgers.edu (128.6.4.4) 
in pub/linux, mg is the binary and mg.tar.Z is the sources file. You
can also find a PD ed, and elvis has an ex mode. Also available is
Lucid Emacs (available on sunsite.unc.edu in
pub/Linux/apps/editors/lemacs), including binary and info and lisp
trees (it takes about 18MB of disk space). Finnally there are
joe, vile-3.11, elle (Elle Looks Like Emacs), Xedit and aXe.

VIII.07)  Does there exist a printer package for Linux?

ANSWER: (R. Miller) Yes.  The "plp" package is currently available
under the directory [/pub/linux]/BETA/plp on tsx-11 and its mirrors.
You may also print things manually like so:  cat filename > /dev/lp1 
(Note that though "/dev/lp0" exists, most people find that their
printer is on /dev/lp1.  Use whatever the kernel says that it detects
in the boot-up messages.) 

VIII.08)  Are uucp, mail, and/or USENET news available for Linux?

ANSWER:    Yes !!!  Read the section UUCP/NEWS/MAIL for LINUX in this
FAQ. Moreover if you are interested in the last uucp features, join
the UUCP channel (see  part1 of this FAQ for more details about the
multi channels list). 

VIII.09)  How do I make swapping work?

ANSWER: Quite simply, you need the swapon and the mkswap binaries.
Then you can choose between a swap partition or a swap file.
The mkswap is used to write the "swap signature", whilst the swapon
binary is to activate the swapping. 

First of all you need a partition :), I assume it's the second of your
first disk namely /dev/hda2, and it's 10MB big
A) swap partition:
you have to indicate it's a swap area, this is done via mkswap
(instead of mkfs) which needs the name of the partition and the size
in blocks (a block is 1Ko big); the optional -c flag is for bad block
checking. So for our example you should perform:
mkswap [-c] /dev/hda2 10000
Then you need to indicate that you want linux to use the swap area,
this is done via swapon. In general it is set in the /etc/rc file,
just put the following entry:
/bin/swapon /dev/hda2
It can also be achieved via the /etc/fstab file
B) swap file:
The process is quite close; you need a partition, and a swap file.
Assume that I prefer a swap area of 4MB (I want to keep some place in
/dev/hda2). I need first to "dd" the file.
dd if=/dev/hda2 of=/swap_file bs=1024 count=4096
bs stands for block size, and count is the number of blocks
then I have to put the "swap signature" on that file:
mkswap /swap_file 4096
At this point, you should 'sync', just to be sure the signature is
effective. And finally add an entry in the rc file:
/bin/swapon /swap_file

VIII.10)  When I boot I get one of the following messages:
"Unable to find swap signature" or "Bad swap-space bitmap"

ANSWER: You probably forgot to make your swap-device, use the mkswap
command. 

VIII.11)  How do I know if it is swapping?

ANSWER: You will notice it :)) First of all, Linux tells you at boot
time, "Adding swap: XXX pages of swap space", and if you start running
out of memory, you will notice that the disk will work overtime, and
things slow down. Generally a 2Meg RAM will make the system swap
constantly while running gcc, 4 Meg will swap occasionnaly when
optimizing big files (and having other things active, such as make).
Also, the command 'free' (from the ps package) reports total enabled
swap space and current swap use.

VIII.12)  How is it possible to remove a swap file?

ANSWER: Simply perform a rm on that file, and remove the swapon of
your /etc/rc file.

VIII.13)  How is it possible to remove a swap device?

ANSWER: mkfs the device, and remove the swapon of your /etc/rc file.

VIII.14)  How much swap space do I need ?

ANSWER: Linux does not perform real swapping, it's rather paging (see
below for a more complete explanation). The swap area is *added* to
the memory and can be viewed as virtual memory, so choose the size you
need, example:

		8MB RAM + 6MB swap => 14MB virtual memory

VIII.15)  Could someone explain the swap process on Linux?, is it
swapping or paging ?

ANSWER: (Linus) Linux uses swap as /additional/ memory, one page of
the swap-space is used for the good-page bitmap and the swapspace
signature. 
In fact Linux does only paging, no swaping in the meaning "write out
one whole process to disk".
The reason it's called swapping is that Linux used paging for memory
management on a low level since the very beginning, but didn't page to
disk at all until 0.12. 

VIII.16)  Is demand paging different from paging and How ?

ANSWER: (Linus) Demand-paging is really "demand loading of
executables" and is totally independent of the page-swapping
algorithms, although they have similarities. When Linux strts up a
process, no actual code space is loaded: I let the page exceptions
load in the executable as needed. Thus Linux demand-loads the code and
initialized data it needs.
Demand-loading has very good points: (a) it simplifies the exec system
call; (b) it means page sharing between that have excuted the same
file is easy to implement; (c) it cuts down on the amount of memory
required. When Linux runs out of real memory, it starts to lock for
pages it can swap out, but if it notices that the page is clean, it
just forgets about it, and demand-loads it when it's needed again.
Thta means that swap-file isn't needed as much, especially when
running big binaries such as gcc, where the code-pages can be
demand-loaded as you wish.

Point (c) means that even without any swap space, you can usually run
slightly larger programs that your memory setup would actually permit.
I've noticed this while running X and doing a kernel compilation +
something else wshen I've forgotten to turn on swapping: free reports
0 page available but things still work, although performance is
slightly down... 

VIII.17)  Is there any way to tell how much swap space you are using
or have left? 

ANSWER: The free program provided with the ps package handles this.

VIII.18)  I have a 2Megs box, but "free" reports only 1Meg why?

ANSWER: (Linus:) "free" doesn't concern with the memory the kernel has
allocated for itself. In other words what you see is the *user* memory
available. The kernel has taken the low 1Meg for it's use (~250Ko for
it and the rest for buffer cache and kernel data structures); for big
memory machine it could be even 2Megs.

VIII.19)  What tape drives work with Linux ?

ANSWER: (24 sept. P. Riipinen)
- There is a working QIC-02 device driver for Linux, supporting (at
  least) Everex/Wangtek cards.
- There are additional patches for the QIC-02 to support Archive
  SC402/499R. You can find them in /pub/linux/alpha/qic-02 at tsx-11
  There are some bugs in the driver but you can backup.
- Newer drivers are all SCSI, so check the SCSI section in this FAQ.

VIII.20)  Is there a driver for my Colorado Jumbo tape drive ?

ANSWER: (Charlie Brady 93/06)
Not at this stage, although some are trying. The Colorado Memory
Systems tape drive connects to the standard floppy disk controller as
a third device on the cable. Similar drives are sold by Irwin,
Mountain, Wangtek and others and they are collectively known as QIC-40
and QIC-80 drives. The medium is a DC-2000 or DC-2120 minicartridge.
There is a pre-pre-alpha version of a driver, and appropriately
skilled volunteers are encouraged to try to finish it.  Be warned, the
timing constraints of the interface may be a significant problem.

VIII.21)  Is there only the %$#@ keyboard ?

ANSWER: There are Dannish, Finnish, French, German, Uk, US and DVORAK 
keyboards. Set it in the main Makefile of the kernel sources, then  
(re)compile the kernel again. Make sure the files in kernel/chr_drv
directory are recompiled.   

VIII.22)  (special FINNISH/US) I booteed up with the new image and
everything work except that some keyboard keys produce wrong
characters. Does anyone know what is happening?

ANSWER: Since 0.95a images are US product (and so are US-keyboard
oriented), BUT linux sources are FINNISH product, and so the default
keyboard is set to be FINNISH. The solution is in the previous Q/A.

VIII.23)  Does there exist shared libs ?

ANSWER: (H.J. Lu, [email-masked], 09/01/92)

The shared library under Linux started at 0.12. Peter MacDonald
collaborating with Linus made the first generation of shared library,
which is the base of the classic shared library which is no longer widely
used.

The kernel support of shared library under Linux is system call

extern int uselib (const char *__filename);

which loads an executable image with fixed entry point into memory,
just like the ordinary executables.

In crt0.s, a function which can find out if and which shared images
are needed and loads them is invoked before `main ()' is called if
necessary. David Engel and I developed a way to tell the loader which
shared images have to be loaded, utilizing the similar technique used
in global constructor in g++ 2.x with the help from GNU binary
utilities.

In the classic Linux shared library, we build a big executable image 
for several libraries and make sure no external variables outside of
the participating libraries are referenced. Then we can get the
absolute addresses of all the global variables defined in the
libraries used to build that executable image. After that, we make a
stub library for each participating library which just has the
absolute addresses of all the global variable in it.

For each shared image, there must be one and only one .o file, which
defines a global variable containing version, name and entry point of
the shared image, and a dummy global data. Among those libraries used
to build the shared image, there must be one library which will always
be referenced whenever any other library is referenced. We put this .o
file into the stub library for that library and add a special symbol
to each of the components of the stub library in order to make sure
that this .o file is always linked in if any of the participating
libraries are linked.

In gcc 2.2.2d, jump table, developed by David Engel, was introduced in 
the shared library. At the beginning of each shared image, there is
a table in which every library function has a fixed entry address and
the instruction at that address is a jump which will lead to the
real library function. So we can change the library function without
changing the corresponding entry address of the jump table. For the
global data we put them at the beginning of data section of the shared
image. We have to separate them from text code and link them in fixed
order. It is very hard to maintain the same addresses for the global
data when library is changed. After the global data are set up properly
and some spaces are left for possible future changes (that is a very
tough procedure.), it isn't too difficult to maintain.

Starting with libc.4.3, a form of dynamic linking developed by Eric
Youngdale was introduced into the shared libraries.  As part of this,
the tools that were used to generate the sharable libraries were
completely redone which made the job of building the libraries much
easier, and thus the libX*.so.3.0 libraries were made as DLL jumptable
libraries.

VIII.24)  Why do I need dynamic linking.

ANSWER: The best way to illustrate this is with a simple example of
what happens without dynamic linking.

	#include <stdio.h>

	int errno;
	FILE * foo;

	main(){
		foo = fopen("/usr/bin/foo","w");
		printf("foo: %x errno: %d\\n",foo, errno);
	}

Assume this program is run by a non-root user. Normally you would
expect that the open will fail because the user does not have
permission to write to /usr/bin - this means that fopen() would return
NULL, and errno would contain 13, which means EACCES - Permission
denied. If you link this to a normal jump table library, it prints

	foo: 0  errno: 0

Now consider the following nearly identical program:

	#include <stdio.h>

	extern int errno;
	FILE * foo;

	main(){
		foo = fopen("/usr/bin/foo","w");
		printf("foo: %x errno: %d\\n",foo, errno);
	}

The results for this program are:

	foo: 0  errno: 13

Why does this happen???. First of all you must realize that in the
first program errno is not declared external, and thus storage will be
allocated in the data segment for the variable. Unfortunately there
is no way to tell libc this, and libc has it's own storage for errno.
Thus libc writes the result in one location and you are looking in the
other. In the second program errno is declared extern, and thus no
storage will be allocated. The linker will see the need for a
definition of errno, and it will find one in libc. Thus in the second
example the user program is reading the same memory location that the
library stored the answer in.

This is of course a simple example. There are more complicated
examples involving programs that want to redefine a library function
and these can lead to quite bizarre behavior which is difficult to debug.

With dynamic linking, both of the above programs yield the same
(correct) result.

VIII.25)  How does dynamic linking work under linux?

ANSWER:  Basically, to implement dynamic linking we need to route all
function calls to global functions through the jump table. We also
need to make sure that all global data is accessed indirectly through
a pointer. The actual libraries do not really look very much
different from the actual jump table libraries that we are currently
using, but there are additional pointers to the global data in the
sharable image that are used internally by the library to access all
global data. There are also additional symbols in the stub library
that are defined as the address of the various pointers, and are used
by the linker to help determine whether there is a pointer or a jmp
instruction that needs to be fixed up.

	The linker has one new important task with dynamic linking.
It watches for duplicate definitions of symbols, and if the
second definition is in a sharable library, it makes a note of it as a
conflict that needs to be resolved at run time. The linker puts a list
of all of these conflicts into a table and makes it available to crt0
through the variable __SHARABLE_CONFLICTS_.

	At run time, crt0 (through the function __dynamic_resolve)
will go through and fix up all of the pointers that need to be fixed.
Let us say for example that you define your own malloc function in a
program - in this case at run time the startup code will actually
modify the jmp instruction in the jump table so that it points to the
malloc function in your program, not the one in the library.  The
library will never refer to the malloc function directly, but it will
always be referenced through the jump table - in this way we ensure
that there will only be one function named malloc that is used by a
given program.

	If you were to run the first example program in the "Why do I
need dynamic linking" answer, then the pointer in the library that
corresponds to the variable errno will be modified so that it points
to the errno variable that is in your program.  The library itself
will never use errno directly - it will always use it via the special
pointer variable.  In this way we ensure that all references to the
variable errno both in your program and in the sharable library will
reference the same memory address.

VIII.26)  Does Linux work for SCSI drives?

ANSWER: Yes since v0.96. Read the section devoted to SCSI in this FAQ
(check the TOC file to find the section).

VIII.27)  Linux is supposed to work with ESDI drive. However I have
trouble with my Magtron MT-4115E (Joincom controler), any clue?

ANSWER: (Linus) Some harddisk don't like linux (even though they
should). Maybe not a bug but a deficiency.
(Mika) I had to remove the printk "unexpected hd interrupt" statement
in hd.c because I was getting so many of those messages. Be warned
that if there is any read error the system just hangs, even the
ctrl-alt-del won't work. You should be able to use your ESDI drives if
you could live with those nuisances.

VIII.28)  How does one go about applying a patch to Linux ?

ANSWER: (Drew Eckhardt) In the unix world most of distribution are in
source form. This includes the operating system. To apply a patch, you
apply it with the 'patch' program to the affected sources. The patch
program takes as input the differences between the old and the new
version. After patching you need to recompile the sources.

Assume I want to apply a patch enclosed in the file XXX. First of all
I will look at the top of XXX, where the file affected is identified.
This may have aleading path attached to it. Either cd out to the
"root" of the patch, ie if I see
linux/kernel/blk_drv/blk.h

I would cd into /usr/src 
(assuming it's the place where I can find linux/kernel...) 
and then patch as follows
patch -p0 < whatever_place/XXX

or, you can specify a number of path components to strip from the
path. If I am in the blk_drv directory patching would be
patch -p3 < whatever_place/XXX

VIII.29)  There are a lot of patches available (ps patch, NFS patches,
CD-ROM patches ...) can I be fairly confident the subsequent patches will
work?

ANSWER: This is not true yet for the current version; but it will be
so I kept it :) 
No you can't, patching is a real beta tester art :)).  People are not
working on the same patched release, so you have to check if the
patches you already applied works on the same kernel part, if not,
/great/, just apply them. If yes, check if there is an order, patch
creator knows that, and (should) try to warn patch user (in other
words: beta tester) otherwise you should edit the patch files (and
possibly make a brief note to others on this list/newsgroup or even a
cdiff) before applying them, another solution is to keep cool and wait
for the next version of Linux where, in general, the modifications
have been done but this behavior is /not/ Linux helpful.

VIII.30)  I got the patches on some ftp sites, and applied them to the
kernel and tried to compile. It didn't !!. Are the patches buggy?

ANSWER: Before remake, just do a make clean in the directories
involved by the patches. This will force a rebuild of the .o and .a
files. 
If you have a RCS running on your source tree, did you checked a
patched version of the files changed before /any/ CO either by you or
make

Finally, make sure the patches succeded. Normally, failed patches on a
file FILE will leave a FILE# file. Moreover you will get a "chunk
failed" message. It is possible to capture the output while patching,
with the following:

	patch -p0 < patchfile | 2>&1 patch.result | more

VIII.31)  What is VFS?

ANSWER: (Ted) Linux 0.96 already has Virtual FileSystem, which means
that it acts as a filesystem switch. It makes it easy for someone to
design another filesystem format and include it in the Linux kernel
along with the standard minix filesystem format. So it /enables/
someone to design a robust filesystem which would have some nice
properties (no 14 chars file name limitation, nor 64Meg limit), and
could be included in the kernel in such a way that both the Minix and
the new one could be mounted at the same time. This solves the
uncompability problem; since the root disk could still use the Minix
filesystem, while the hardisk could be using the new one.

VIII.32)  What's about Bus Mice ?

ANSWER: (Nathan I. Laredo) Since the Linux v0.96c-pl2 the kernel does
support LOGITECH and BUS MICE 
If you are unsure that you have a bus mouse or not, check to see if
your mouse card has a selection for a sample rate switchable between
30Hz and 60Hz (or possibly 25/50Hz), if it does not, then it is NOT a
true  bus mouse (InPort mice for example will not work with this
driver). 
To create a bus mouse device:
mknod /dev/mouse c 10 0

VIII.33)  What's about TeX ?

ANSWER: The primary site for Linux TeX is 129.78.66.1, this is 
P. Williams' site in Australia. The stuff at tsx-11 was posted by 
T. Dunbar  who does support/maintain the dvilj stuff.

VIII.34)  What's about LILO ?

ANSWER: (Werner Almesberger)
LILO  -  Generic Boot Loader for Linux ("LInux LOader") 

This is an ALPHA test release of a new boot loader. Be sure to have
some means to boot your system from a different media if you install
LILO on your hard disk.

Features
--------

- does not depend on the file system. (Tested with Minix, EXT FS and MS-DOS
  FS.)
- can be used to boot from floppies and from hard disks.
- can replace the master boot record.
- can boot non-Linux systems (MS-DOS, DR DOS, OS/2, ...) and unstripped
  kernels.
- supports up to 16 different boot images that can be selected at boot
  time. Root and swap disk/partition can be set independently for each
  image.
- boot sector, file map and boot images can be all on different disks or
  partitions.

Restrictions and known problems
-------------------------------

- SCSI disks are not fully supported yet. (Still waiting for some kernel
  changes.) (Should work in current release - EY).
- booting other operating systems doesn't seem to work everywhere. If
  everything but booting a non-Linux OS from LILO works on your system,
  you should boot LILO by BOOTACTV and select the alternate OS with the
  latter as a temporary work-around.
- booting non-Linux systems from the second hard disk ("D:") is not yet
  supported.

Please send all bug reports to [email-masked]

VIII.35)  What's about MGR ?

ANSWER: (General Information grabbed from various sources)
There is a MGR channel available , contact the request adress with
help in the body: [email-masked] 
The stuff can be found at tsx-11 in pub/linux/packages/MGR
In brief:

MGR provides:
	- multiple overlapping windows
	- multiple fonts
	- text and graphics in each windows
	- a simple popup menu package
	- a client/server model 'a la' X
	- independance from any peculiar networking technology

MGR consist of a server process and some clients. Each client has his
own window, and can create subwindows. Clients communicate with the
server via a bidirectionnal channel. A C library is provided.

When a new window starts, it is as a terminal emulator running the
shell; for more information you can grab the mgr-man.out from
bellcore.com 

The information hereafter appeared on the MGR channel on 19th Jan. 
> From: [email-masked]
> Subject: MGR 0.53
>
>
> MGR, version 0.53 for Linux and SunOS (Coherent unfinished yet).
>
> Unpack the src* stuff under in /src/lbin/mgr and the usr* stuff in 
> /usr/mgr.  I splitted things that way for making it easier to ftp
> them and carry them home.  If you don't like these paths, then use
> others, but remember to edit the Configfile after generating it. 
> YOU NEED TO INSTALL ALL FILES FOR COMPILING.
>
> This is a beta release for programmers, there are no binaries.  It
> makes my work available for people who either also work on MGR and
> like to get new sources and for adventerous beta testers.  WARNING:
> I assume using Linux 0.99.2 and GCC 2.3.3.
>
> There is some new m4 code to generate menus.  It is more powerful
> than menu(1), but a little harder to use.
>
> MGR is currently being ported to Coherent 4.0, but this version
> doesn't include everything yet.  There is already a beta version
> running on Coherent, although not too stable yet.
>
> For questions, write to the mailing list, channel MGR.  Please be
> sure to talk about the latest version of MGR plus having read the
> README files in the directories containing the problem.
>
> You got this stuff from ftp.thp.uni-koeln.de:pub/linux/mgr or from 
> tsx-11.mit.edu:~ftp/pub/linux/packages/MGR, which is a mirror of the
> Cologne directory.

VIII.36)  I have successfully compiled MGR, but when I try to run the
program I get "can't find mouse" or "already in use", any clue?

ANSWER: try the following "mgr -m /dev/ttys1" if the mouse is on
the serial 1. Another possibility is to link /dev/mouse with
/dev/ttys1 (assuming your mouse is on serial 1). Or if it's a bus
mouse, "mknod /dev/mouse c 10 0" once.

VIII.37)  Any tips for MGR?

ANSWER: Well, I have tried it on my 386Sx Ega/Vga; the screen is Ok
but the Logitech mouse I have is not well recognized.

BTW check the major/minor number for pty's; they should be character
device with 4 as major and 128 and bigger as minor:
ptyp0 c 4 128
ptyp1 c 4 129
...
ttyp0 c 4 192
ttyp1 c 4 193

VIII.38)  What's about X11 ?

ANSWER: See the section XII. devoted to X11 in this FAQ.

IX. GCC MISC INFORMATION
========================

**** Last update 93/03/26

IX.A. HLU Information
IX.B. OTHERS

IX.A. HLU Information
~~~~~~~~~~~~~~~~~~~~~

The official release of GCC for Linux is 2.3.3.
This section includes:
	README.gccdisk
	FAQ of gcc written by HLU

  IX.01)  I don't know how to install gcc stuff, is there special
places?

ANSWER: This is the README.gccdisk

                    Linux GNU C/C++ [HJ release]

Introduction
------------
  This is GNU C/C++ 2.3.3. It is linked with jump table 4.2. You should use
  it with the Linux C library disks since the C/C++ compiler has no shared
  images, which are required by all the binaries in it.  It consists of
  2 minix disks, which will fit on either 5.25" or 3.5" floppies.

  It is on tsx-11.mit.edu under pub/linux/GCC/gccdisk

Distribution File Format
------------------------
There are two files, each of which goes on one disk

  A. Disk 1 (gcc233a.Z)

  This contains gcc, cpp, cc1 and crt0.o/gcrt0.o.  There are also some header
  files in /usr/lib/gcc-lib/i386-linux/2.3.3/include.

  B. Disk 2 (gcc233b.Z)

  This disk contains cc1plus.

Installing on the Hard Drive
----------------------------------------
  1. uncompress base[1|2].Z.
  2. rawrite or dd each file to a formatted floppy disk.

  Now you have made a copy of gcc 2.3.3 on two floppies.  To copy each
  floppy to your hd, you should mount the floppy and copy its contents to
  your hard drive.  You can do this by:

    mount /dev/fd[0|1] /mnt
    cd /mnt
    for d in bin dev etc usr
    do
      if [ -d $d ]; then
        cp -av $d /
      fi
    done

  Note: This may overwrite some files on your hard disk.

Thanks.

H.J.
[email-masked]
12/31/92

  IX.02)  What compiler should I use for Linux?

ANSWER: You should only use the same version on tsx-11.mit.edu under
/pub/linux/GCC. If you want to use the testing release, first join
the GCC channel on the Linux mailing list, and then send a note to
[email-masked]. Don't use gcc older than the one on tsx-11.mit.edu.

  IX.03)  Where is the latest official gcc 2.xx for Linux?

ANSWER: It's on tsx-11.mit.edu under /pub/Linux/GCC and under
pub/linux/GCC. You may find it on the other sites. Since gcc 2.3.3,
you can compile it yourself out of box from any gnu ftp sites. Just
unpack the source code and do

	configure [i386-linux|i486-linux]

You should follow the instructions in INSTALL.

  IX.04)  Where is the latest official Linux C library?

ANSWER: It's on tsx-11.mit.edu under /pub/Linux/GCC and under
pub/linux/GCC. You may find it on the other sites.

  IX.05)  What are the contents of them?

ANSWER: Please read the current release note and ChangeLog for
details.

  IX.06)  How do I install them?

ANSWER: Read README and release notes.

  IX.07)  What are the main differences with the old release?

ANSWER: Read README and release notes.

  IX.08)  Can I use the old version of gcc?

ANSWER: Please get rid of gcc older than gcc 2.2.2. Starting from
gcc 2.2.2, you can do

	gcc -V xxxx

where xxxx is the version number. Please read `release.xxxx' for
detail. There is one catch in gcc 2.2.2d, setjmp/longjmp is changed,
so the old header files is not compatible with gcc 2.2.2. Before you
install gcc 2.2.2d, please do

cp /usr/include/setjmp.h /usr/lib/gcc-lib/i386-linux/2.2.2/include

where /usr/include/setjmp.h is come with gcc 2.2.2.

  IX.09)  Can I delete the old shared image in /lib?

ANSWER: Since the Linux C library version 4.3, we have introduced the
dynamically linked library. There is no need to keep old shared images
in /lib if none of your binaries are linked with the classic shared
library which has been obsolete. You can just keep one version of
the shared image in /lib which has the highest major and minor
release numbers for each shared library. The name of the shared image
is "xxxxxxxxxxxxxxx.so.major.minor".

  IX.10)  Is stdio ANSI compatible?

ANSWER: Yes, please test it.

  IX.11)  Is g++ in 2.xx?

ANSWER: Yes.

  IX.12)  Where can I get the gcc manual?

ANSWER: You can get man pages and manual come with the gcc source code
on any gnu ftp sites. You should find gcc-man.tar.z on tsx-11 which
has man pages for gcc.

  IX.13)  What options can I use for gcc?

ANSWER: Read the manual. There is one special flag for Linux, -static
tells gcc to use the static libraries. The default is the jump table
version of shared libraries.

  IX.14)  How can I debug the C code?

ANSWER: Read the gcc/gdb manuals. The simple way to do is

	gcc -g foo.c -o foo
	gdb foo

  IX.15)  Where is the source code of the new libc.a?

ANSWER: The same place you find this file. It is called
libc-xx.yy.tar.z.

  IX.16)  Why does g++ complain, even die?

ANSWER: You need "expr", which is in GNU shell utilities 1.6, echo (?)
and sed.

  IX.17)  How do I generate code for 486?

ANSWER: Add -m486 to CFLAGS.

  IX.18)  I heard malloc (0) wouldn't work with Linux, what should I
do?

ANSWER: It *does* work in a manner which POSIX allows; unfortunately,
pre-POSIX code frequently assumes that malloc(0) will not return
0 -- the standard version of malloc under Linux *does* return 0.
By including <stdlib.h>, you get a definition of malloc which behaves
more traditionally.  If you define NO_FIX_MALLOC, then you will get
the default (non-traditional) form.  If you are trying to develop POSIX
compliant code under Linux, you should probably define NO_FIX_MALLOC to
ensure that your code doesn't make assumptions about malloc() which
will not work on other systems.  (Note: NO_FIX_MALLOC is specific to
Linux.)

(Provided by [email-masked]. Thanks.)

  IX.19)  Why does gcc say "xxxxx..h not found"?

ANSWER: see QUESTION: What are the contents of them?

  IX.20)  I really followed every step in the documentation, but when
I do "make", why does it say "don't how to make xxxxxx"?

ANSWER: The dependency in Makefile is dated, you need to make a new
one. Please get some guide on make and read Makefile. For the kernel
sources, please do

cd src/linux
make dep

  IX.21)  How do I compile programs under Linux?

ANSWER: The Linux C library is trying to be ANSI/POSIX compliant. It
is also very compatible with SYSV and BSD. The C library is loaded
with SYSV and BSD functions. There are three exceptions:

1. signal in Linux is POSIX.
2. tty in Linux is POSIX.
3. time functions are POSIX, plus a few BSD and SYSV extensions.
4. setjmp/longjmp functions are POSIX. But you can use -D__FAVOR_BSD
   to make it BSD or use sigsigjmp/siglongjmp.

When you compile a program under Linux, your best bet is include all
the appropriate header files and use -Wall. All the usable functions
and global variables are declared in the corresponding header files.
YOU SHOULD NOT DEFINE ANY functions or global variables OF THE LINUX C
LIBRARY IN YOUR CODE IF YOU WANT TO USE THE SHARED LIBRARIES.

After saying all those, you now should know you can compile a program
with -D_POSIX_SOURCE or -D_GNU_SOURCE (read <features.h> for details).
With a few modifications you can even use -DSYSV, -DUSG or -DBSD. Some
codes need to define -DSTDC_HEADERS for ANSI C compiler like gcc here.

To use malloc () and calloc () safely under Linux, please include

<stdlib.h> and don't define NO_FIX_MALLOC.

BTW, gcc -traditional should work with gcc 2.2.2d or above.

Please also read ChangeLog for the latest enhancement.

Please read the header files for details. Maybe you should get a book
on POSIX. Any suggestion of the book list?

>From Steve Robbins  --  [email-masked]

--------
I like "POSIX Programmer's Guide", by Donald Lewine.  Its essentially
a list of POSIX functions' man pages, with a very brief guide in the
beginning of a few things.  It's published by O'Reilly & Associates,
Inc.
--------

  IX.22)  How can I get bsd style signal?

ANSWER: Use -D__USE_BSD_SIGNAL.

  IX.23)  Why does a program that should only poll for input become
a CPU hog?

ANSWER: The select() system call. The timeout parameter was classically
used read-only by the system. Some manual pages already notes three
years ago:

       select() should probably return the  time  remaining  from
       the  original timeout, if any, by modifying the time value
       in place.  This may be implemented in future  versions  of
       the system.  Thus, it is unwise to assume that the timeout
       pointer will be unmodified by the select() call.

If you do not take this advice seriously you get a zero timeout written
back to your timeout structure, which means that future calls to
select() using the same timeout structure will immediately return.

Fix:
Put the timeout value into that structure every time you call select().
Change code like

       struct timeval timeout;
       timeout.tv_sec = 1; timeout.tv_usec = 0;
       while (some_condition)
         { select(n,readfds,writefds,exceptfds,&timeout); }

to

       struct timeval timeout;
       while (some_condition)
         { timeout.tv_sec = 1; timeout.tv_usec = 0;
           select(n,readfds,writefds,exceptfds,&timeout);
         }

  IX.24)  When a program is stopped using Ctrl-Z and then restarted,
or in other situations that generate signals: Ctrl-C interruption,
termination of a child process etc. why does it complain about
"interrupted system call" or "write: unknown error" or things like that.

ANSWER: The system call the program was executing has been interrupted
to process the signal, and then it returned -1 and set errno = EINTR.
The program then was likely to draw bad conclusions from that.

Explanation: Your program has signal handlers installed, using
signal() or sigaction(). When the signal occurred, your signal handler
was invoked. In other Unix systems, this usually happens asynchronously
or in a few slow system calls:

  When a signal is caught during the execution of system calls such as
  read(2), write(2), open(2) or ioctl(2) on a slow device (such as a
  terminal, but not a file), during a pause(2) system call or a wait(2)
  system call that does not return immediately because a previously
  stopped or zombie process already exists, the signal-catching
  function is executed and the interrupted system call then returns a
  -1 to the calling process with errno set to EINTR.

Linux (following POSIX) checks for signals and may execute signal
handlers
* asynchronously (at a timer tick),
* on return from *any* system call,
* during the execution of the following system calls:
  select(),
  pause(),
  connect(), accept(),
  read() on terminals or sockets or pipes or /proc files,
  write() on terminals or sockets or pipes or line printer,
  open() on FIFOs or PTYs or serial lines,
  ioctl() on terminals,
  fcntl() with command F_SETLKW,
  wait4(),
  syslog(),
  any TCP or NFS operations.
  [For other operating systems you may have to include the system calls
   creat(), close(), getmsg(), putmsg(), msgrcv(), msgsnd(), recv(),
   send(), wait(), waitpid(), wait3(), tcdrain(), sigpause(), semop()
   to this list.]

In the last two cases and assuming the program's signal handler returns,
the system call returns -1 and sets errno to EINTR.

If the SA_INTERRUPT flag is not set for the corresponding signal,
however, in most cases the system call is automatically restarted
(continued) after execution of the signal handler, and your program
won't see any EINTR.

You may ask why this is not the default behavior when the default
Linux signal () is used to install the signal handler. This is because
POSIX adopted this. As for which one is better, it is a matter of
opinion.

Note that in some versions of BSD Unix the default behavior is to
restart system calls. To get system calls interrupted you have to use
the SA_INTERRUPT flag.

Fix:
Either add -D__USE_BSD_SIGNAL to your CFLAGS. Or for every signal
handler that you install with signal(), use sigaction() instead,
without setting SA_INTERRUPT.

Note that while this applies to most system calls, you must still check
for EINTR on read(), write(), ioctl(), select(), pause(), connect().
You may do it like this:

         int result;
         while (len > 0)
           { result = read(fd,buffer,len);
             if (result < 0) break;
             buffer += result; len -= result;
           }
   -->
         int result;
         while (len > 0)
           { result = read(fd,buffer,len);
             if (result < 0) { if (errno != EINTR) break; }
             else { buffer += result; len -= result; }
           }

and

         int result;
         result = ioctl(fd,cmd,addr);
   -->
         int result;
         do { result = ioctl(fd,cmd,addr); }
            while ((result == -1) && (errno == EINTR));

IX.B. OTHERS
~~~~~~~~~~~~

  IX.25)  I seem to be unable to compile anything with gcc. Why?

ANSWER: If you have only 2 MB RAM, gcc will die silently without
compiling anything. You must have at least 4 MB to do compilations

BTW Since swapping is possible, I have heard that compilation works 
with only 2Meg and a lot disk traffic :) Isn't it great?

  IX.26)  gcc complains about not finding crt0.o and the system
include files What am I doing wrong ?

ANSWER: The include files normal place is in /usr/include. lib*.a and
*.o should be in /usr/lib or /usr/local/lib

  IX.27)  I tried to port a /new/ version of gnu stuff. But in the
linking phase, gcc complains about the missing libg.a. 

ANSWER: Yes this is well known for compiler version earlier than
2.2.2, throw away the flag -g that's all, anyway libg.a is /only/ for
debugging purpose. 

  IX.28)  How to compile programs which may be debugged with gdb?

ANSWER: There are different ways to handle this problem. If
you have the gcc2.2.2 or later it's simple, use the -g flag. Otherwise
there are different possibilities:
1) As there is no libg.a, you should throw away the -g flag in link
phase, this means that the compilation must be done in two steps
example: instead of "gcc -g monprog.c -o monprog", use the following
"gcc -g -c monprog.c" and then "gcc -o monprog monprog.o"
Alas this method is not that good if you are using Makefile.
2) The other way is to create an empty libg.a as follows (Peter
MacDonald trick):
- create libfake.c containing libgfake() {}
- compile it with: gcc -c libfake.c
- create the libg.a with: ar r libg.a libfake.o
2bis) The more tricky Humberto method:
cd /usr/lib
ranlib libg.a

then gcc -g monprog.c -o monprog will produce a debuggable monprog

  IX.29)  When compiling some code, cc1 complains about some insn
code, what's that? 

ANSWER: An insn is an internal representation that gcc uses when
compiling. The main part of gcc is to take ordinary c (or c++) code,
and compile it, while ding optimizations in insn part, which is
soft/hard independant. Then another part which is hard/Os dependant
takes the insns and translate it in assembly language. The fix is only
to turn off the optimization flag (-O). 

  IX.30)  When compiling #$@!, I've got some problems with "SIGBUS"
signal that doesn't exist. Any clue ?

ANSWER: (Louis J. LaBash, Jr.) SIGBUS is a common problem, its not
needed, just comment it all out, something like:

#ifdef SIGBUS
.. normal sigbus code ..
#endif

  IX.31)  How can I write codes suitable for building shared library ?

ANSWER: (Eric Youngdale, [email-masked], 3/1/93)
  
In general there are very few restrictions as long as you are using the
new tools for building sharable libraries.  Before the DLL libraries were
available there were all kinds of things you had to watch out for, but
currently you can more or less build a sharable library out of the box
without making any source code modifications.  See the README in the
tools-m-n.tar.z distribution for more information on how to build a
sharable library.  

X. SCSI SPECIAL
===============
*** This section is written by Drew Eckhardt, mail him for
*** information, questions related to this section.
*** Last update May 1993.

   X.01)  What hardware is supported?

ANSWER: The Adaptec 154x, Adaptec 174x, Future Domain 8xx (TMC 
950 based boards?), 16x0,  Seagate ST0x, Ultrastor 14F (Some of the 
new ALPHA code makes attempts to deal with the 34F) and Western Digital 
7000 are supported.  Various Adaptec clones from Bustek and Future Domain 
are known to work, in both ISA and EISA flavors.

There is an alpha driver for the Ultrastor 24F -

tsx-11.mit.edu:/pub/alpha/scsi/u24f-driver.tar.z

Some of the SCSI drivers will not autodetect your SCSI host if the 
BIOS is disabled, and there may be IRQ, DRQ, address restrictions 
compiled into the distribution kernel.

Virtually all SCSI disks, CD ROMS, and tapes should work.

   X.02)  What hardware is not supported?

ANSWER: The Adaptec 152x, 151x, Always IN-2000, DTC, Mylex, PS/2 SCSI boards, 
all SCSI ports on sound boards, the trantor parallel->SCSI adapter, Rancho 
SCSI boards, Grass Roots SCSI boards, Trantor SCSI boards, etc.

Someone is working on a driver for the IN-2000, if you want to run Linux 
on one of the other boards, you'll have to get technical
docs on it, and write a driver yourself or bribe someone to do it.

   X.03)  How do I get SCSI information?

ANSWER: Subscribe to the SCSI channel of the linux-activists mailing list.
mail [email-masked] 
And put in the header.
       X-MN-Admin: join SCSI

   X.04)  Where is the latest version maintained?

ANSWER: tsx-11.mit.edu:/pub/linux/ALPHA/scsi

Please join the SCSI channel of [email-masked] before you 
grab anything.

   X.05)  I've found one of the following bugs :

- I can't swap to a SCSI disk, or mount one as /

- I get a READ CAPACITY FAILED message on bootup.

- I have a removeable disk (ie Sysquest) and have problems when I change
	media.

- I have a Seagate / Future Domain TMC-88x and the kernel panics with a 
	kernel paging message.

- I have an Adaptec 1742 and am experiencing data corruption

- I have an Insite floptical drive and it won't work.

- I have a TANDBERG TDC 3600 revision U07, SONYCD-ROM CDU-541 revision
	4.3d, DENON DRD-25X revision V, or a SEAGATE ST296 revision
	921 and the system hangs or reports multiple devices.

- My Adaptec 1542C isn't recognized.

ANSWER: All of these bugs have been fixed, so UPGRADE.  

   X.06)  What do I do if I find a bug that still looks like a 
bug after I've read the FAQ?

ANSWER: Your best bet is to send it to the SCSI channel of the mailing list,
where it will be seen by all of the people who've contributed to the 
SCSI drivers. 

In your bug report, please provide as much information as possible
regarding your hardware configuration, and all of the messages that 
Linux prints when it boots.  Your chances of getting the bug fixed increase 
exponentially with the amount of information provided.  

The bottom line is that if we can't reproduce your bug, and you can't 
point at us what's broken, it won't get fixed.

   X.07)  What SCSI disks are supported? 

ANSWER: Disks up to two terabytes in size will work, since the sd driver
switches to 10 byte reads when necessary.

Flopticals, Bernoulis, Sysquests, and other removeable media devices 
are supported by the normal SCSI disk driver.  

   X.08)  What about CD ROMS?

ANSWER: CD ROMS are supported. The ISO-9660 file system with Rockridge
extensions is supported.  You will have to make sure that you have 
configured the kernel to include the isofs filesystem or otherwise you 
will not be able to use the cdrom.

   X.09)  What about SCSI tapes ? 

ANSWER: Tapes are supported.  You may wish to obtain the utility program mt,
which is usually available from tsx-11.mit.edu in pub/linux/ALPHA/scsi.

   X.10)  How do I partition the disk?

ANSWER: Use fdisk, efdisk, pfdisk or the DOS parititioning program of 
your choice.

   X.11)  The linux partitioning programs don't work.

ANSWER: Some of these default to /dev/hd*, which are disks on 
WD-1003 compatable controllers (IDE, MFM, RLL, ESDI, etc), rather
than /dev/sd* (SCSI disks).   Your solutions are to 

1.  Call the partitioning program with a device name, ie 
	pfdisk /dev/sda

2.  Make links from /dev/hd* to /dev/sd*.  

   X.12)  My partitioning program can't figure out the disk geoemetry

The problem with partitioning SCSI disks and Linux is that Linux talks
directly to the SCSI interface.  Each disk is viewed as the SCSI host
sees it : N blocks, numbered from 0 to N-1, all error free.  There is
no portable way to get disk geometry.  

However, DOS doesn't like things like this, it demmands that BIOS
present it with a normal Cylinder / Head / Sector coordinates.  So,
BIOS does, and it comes up with some fabrication that fits what DOS
wants to see.  You don't want to disagree with what BIOS thinks when
you write the partition table. 

The newest SCSI code will return the mapped geometry for some host 
adapter / disk combinations.  Kernel release 0.99 and later should have
this capability.

QUESTION :  I can't make a filesystem on /dev/hd*

ANSWER : /dev/hd* aren't your SCSI disks.  /dev/sd* are. 
See below for approproate major / minor numbers if they 
do not exist on your root diskette.

   X.13)  What are the major / minor numbers for SCSI drives?

ANSWER: Because of the large number of devices that can be hung off of 
a SCSI bus (as many as 56 if you use SCSI fanouts or bridge boards), 
and the possibility of 16 partitions on a SCSI disk, we'd run out of 
minor numbers if they were statically allocated - so a dynamic 
numbering scheme is used.

Block device major 8 is used for SCSI drives, 11 for CD-ROMs.  
Character device major 9 is used for SCSI tapes.
        
Minors are assigned in increments of 16 to SCSI disks as they are
found, scaning from host 0, ID 0 to host n, ID 7, excluding the host
ID.  Most hosts use ID 7 for themselves.

A minor where minor mod 16 = 0 is the whole drive, where minor mod 16
is between 1 and 4, that partition, extended partitions dynamically
assigned from 5 to 15 inclusive.  Note that the gendisk.c module
prints partition tables on initialization - you should be able to see
them there.

Example : I have three SCSI disks, set up as follows 
        Seagate ST02, ID=0
        Seagate ST02, ID = 5
        Adaptec 1542, ID = 0

The first disk on the seagate at ID 0 will become minors 0-15
inclusive, the second at ID5 16-31 inclusive, the disk on the
Adaptec 48-63.

   X.14)  My tape drive or other removeable media device isn't recognized
at boot time.

ANSWER: Try booting with a tape in the drive.

   X.15)  How do I reduce kernel bloat and eliminate the drivers I
don't want?

ANSWER: For kernel release 0.99 and later, just go to the to directory
in the kernel source tree, and type ``make config'', and answer the
questions.  For older kernel distributions, simply #undef
CONFIG_DISTRIBUTION in include/linux/config.h, and define the macros
for the SCSI hosts you want enabled.

   X.16)  I get SCSI timeouts.

ANSWER: Make sure your board has interrupts enabled correctly, and 
that there are no conflicts with other devices (Sound boards 
and serial boards sometimes try to use IRQ5).

   X.17)  My Seagate / Future Domain TMC-88x board is not detected.

ANSWER: The Seagate and Future Domain boards have memory mapped 
registers.  To detect them, Linux scans for a signature in the 
ROM BIOS (typically, a copyright message) and sets the register
addresses relative to that.  

This can fail for two reasons
1) If the BIOS is disabled.  

In this case, you should edit kernel/blk_drv/scsi/Makefile and 
add -DOVERIDE=x -DCONTROLLER=y where x is the base address of your 
controller (the factory default setting is 0xc8000) - note that 
this is *not* the segment (ie, 0xc800), and y is the controller 
type, either SEAGATE or FD.

2) If we don't know about your BIOS yet

Please use DOS and DEBUG to find us a signature that will detect 
your board - 

Ie, if your board lives at 0xc800 do

debug
d c800:0
q

and send me ([email-masked]) the nearest convienient
ASCII message, with the length and offset from c800:0 or 
whereever.

   X.18)  The Seagate / Future Domain TMC-88x driver doesn't work.

ANSWER: There are several possibilities
1) Is the board jumpered for IRQ5 ? 

The factory settings are for MSDOS, and have interrupts disabled.  

On the Seagate, Interrupts are controlled by the W3 (ST01) or JP3 (ST02) 
jumper.  Shorting pins F-G selects IRQ5.

2) Cached machines will not have problems if the Seagate's address
space (typically C8000 - CAFFFF) is not marked "non cacheable."
This applies to the i486 internal cache as well as i386/i486 
external caches.

This can be set in the XCMOS of most machines.  If you can't disable
cache for the Seagate's area (16K in size, starting at the base
address), then you must disable the cache entirely, otherwise
it won't work.

3) If you've defined -DFAST or -DFAST32 in the kernel, blind transfers 
will be used.  This works fine with most disks, but some won't respond 
fast enough, the read/write will timeout and things will get out 
of sync, resulting in timeouts.  Try recompiling your kernel without 
-DFAST or -DFAST32.

   X.19)  The Adaptec driver doesn't work.

ANSWER: A common source of difficulty is a conflict between two different
boards for an IRQ level, a DMA channel, or an I/O address.  Check the
settings for the boards you have in your system (music boards are
known to use similar IRQ or I/O addresses as the Adaptec.  In the new
scsi code the Adaptec can use any of the IRQ levels that it can be
strapped for, it can use I/O address 0x330 or 0x334, and it can use
DMA channels 5, 6 or 7.

   X.20)  The WD-7000FASST driver doesn't work

ANSWER: According to Keith Smith, 

"There are two different versions of the WD7000/FASST2  One uses a
WD33C93A the other a WD33C93.  Firmware incompatibilities in the board
bios could cause a problem as the former chip fixes some problems that
were discovered on the latter.  We're talking BOARD firmware, as well as
BIOS firmware."

   X.21)  My Ultrastor 14F or 34F isn't detected 

ANSWER: The Ultrastor 14F driver won't probe for an Adapter at address
0x310.  Either move it do a different address, or recompile the kernel, 
adding a rule to kernel/blk_drv/scsi/Makefile

ultrastor.o: ultrastor.c
	$(CC) $(CFLAGS) -DOVERIDE_PORT=0x310 -c ultrastor.c

 
   X.22)  When using a Seagate / Future Domain TMC-88x, why does my system 
hang when syncing to disk?

ANSWER: The Seagate boards are an incredibly brain dead piece of hardware.
They can only generate an interrupt when a target raises the SEL signal.
So, as long as a target is connected, the Seagate driver must spin its 
wheels waiting for the actual data transfer.  Some devices agravate the 
situation by connecting for long periods of time while not doing anything.

   X.23)  My system is dog slow (ie, 60k/sec)

ANSWER: SCSI commands have an incredible amount of overhead.  For 
every command, you need to arbitrate for the bus, select the target,
establish an I_T_L nexus, and send the command.  Processing of that
command may take as much as 1ms on older devices.  Add this overhead
to what you already have coming through the file system, buffer 
cache, etc, and you have a real problem.

To work around this, we needed to maximize the amount of data that 
could be transfered in a single command.  So, we implemented 
scatter-gather, which allows reads/writes from/to contiguous 
disk sectors to non-contiguous buffers.  

This typically gets you a 3-5 fold improvement in performance.

The current kernel has scatter-gather support for the Adaptec, Western 
Digital, Ultrastor, Future Domain 16xx, Future Domain 8xx and Seagate 
boards.

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#	LaBRI 			 |					    #
#  351 cours de la Liberation    |  e-mail:  [email-masked]   #
#  33405 Talence Cedex		 |  e-mail:  [email-masked]    #
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	 There will be a sig when our local net is reliable.
	       For now, I would rather stay anonymous.