The advantage of modules?

The advantage of modules?

[Evan Thompson]

I'd like to know (I know, I'm being slightly off topic, while still
staying on topic, so I'm on topic...er...yes) if there is any
advantage, be it memory-wise or architectuarally wise, to use modules?

I already know the obvious points of if you are creating a distro that
it is usually good to make a very modular kernel for those wishing not
to recompile their kernel, but I was wondering if there were any other
advantages to using modules vs. making a monolithic kernel for a
kernel to be used only on one machine (with no other hardware support
at all)?

Thanks, and sorry if I'm being slightly off topic...
Kernels are fun!  I wish I could learn more!
-- 
+----------------------------------+-----------------------------------+
| Evan Thompson                    |            POWERED BY:            |
| evaner@bigfoot.com               | Linux cd168990-a 2.4.0-ac2 #1 Fri |
| Freelance Computer Nerd          |  Jan 5 11:58:30 CST 2001 i686     |
| http://evaner.penguinpowered.com |   unknown                         |
+----------------------------------+-----------------------------------+
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Re: The advantage of modules?

[Drew Bertola]

My best reasons are...

Development: You don't have to recompile the kernel a billion times
while working on a driver, you just recompile the module.  Also, you
can debug, unload, fix, recompile, reload a module to add or fix
pieces of it all (hopefully) without rebooting.

Practical usage: When I take my laptop on the road I use ppp, so I
load it then.  Most of the time I don't need it, so I don't load it.

Evan Thompson writes:
> I'd like to know (I know, I'm being slightly off topic, while still
> staying on topic, so I'm on topic...er...yes) if there is any
> advantage, be it memory-wise or architectuarally wise, to use modules?
> 
> I already know the obvious points of if you are creating a distro that
> it is usually good to make a very modular kernel for those wishing not
> to recompile their kernel, but I was wondering if there were any other
> advantages to using modules vs. making a monolithic kernel for a
> kernel to be used only on one machine (with no other hardware support
> at all)?
> 
> Thanks, and sorry if I'm being slightly off topic...
> Kernels are fun!  I wish I could learn more!
> -- 
> +----------------------------------+-----------------------------------+
> | Evan Thompson                    |            POWERED BY:            |
> | evaner@bigfoot.com               | Linux cd168990-a 2.4.0-ac2 #1 Fri |
> | Freelance Computer Nerd          |  Jan 5 11:58:30 CST 2001 i686     |
> | http://evaner.penguinpowered.com |   unknown                         |
> +----------------------------------+-----------------------------------+
> -
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> Please read the FAQ at http://www.tux.org/lkml/

-- 
Drew Bertola  | Send a text message to my pager or cell ... 
              |   http://jpager.com/Drew

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Re: The advantage of modules?

[J . A . Magallon]

On 2001.01.06 Drew Bertola wrote:
> My best reasons are...
> 
> Development: You don't have to recompile the kernel a billion times
> while working on a driver, you just recompile the module.  Also, you
> can debug, unload, fix, recompile, reload a module to add or fix
> pieces of it all (hopefully) without rebooting.
> 
> Practical usage: When I take my laptop on the road I use ppp, so I
> load it then.  Most of the time I don't need it, so I don't load it.
> 

Usage: I have seen drivers which require params to work, and you can
only give params if the driver is built as a module (ie,
modprobe xxxxxx io=0x300 irq=5, etc...) because your hard is not
properly autodetected by the module.

-- 
J.A. Magallon                                         $> cd pub
mailto:jamagallon@able.es                             $> more beer

Linux werewolf 2.4.0-ac2 #6 SMP Sat Jan 6 01:38:26 CET 2001 i686

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Re: The advantage of modules?

[Michael Meissner]

On Sat, Jan 06, 2001 at 11:02:15AM +0100, J . A . Magallon wrote:
> 
> On 2001.01.06 Drew Bertola wrote:
> > My best reasons are...
> > 
> > Development: You don't have to recompile the kernel a billion times
> > while working on a driver, you just recompile the module.  Also, you
> > can debug, unload, fix, recompile, reload a module to add or fix
> > pieces of it all (hopefully) without rebooting.
> > 
> > Practical usage: When I take my laptop on the road I use ppp, so I
> > load it then.  Most of the time I don't need it, so I don't load it.
> > 
> 
> Usage: I have seen drivers which require params to work, and you can
> only give params if the driver is built as a module (ie,
> modprobe xxxxxx io=0x300 irq=5, etc...) because your hard is not
> properly autodetected by the module.

For many devices you can specify the parameters at boot time if you use
something like lilo to boot.

-- 
Michael Meissner, Red Hat, Inc.  (GCC group)
PMB 198, 174 Littleton Road #3, Westford, Massachusetts 01886, USA
Work:	  meissner@redhat.com		phone: +1 978-486-9304
Non-work: meissner@spectacle-pond.org	fax:   +1 978-692-4482
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Re: The advantage of modules?

[Michael Meissner]

On Fri, Jan 05, 2001 at 10:50:20PM -0600, Evan Thompson wrote:
> I'd like to know (I know, I'm being slightly off topic, while still
> staying on topic, so I'm on topic...er...yes) if there is any
> advantage, be it memory-wise or architectuarally wise, to use modules?
> 
> I already know the obvious points of if you are creating a distro that
> it is usually good to make a very modular kernel for those wishing not
> to recompile their kernel, but I was wondering if there were any other
> advantages to using modules vs. making a monolithic kernel for a
> kernel to be used only on one machine (with no other hardware support
> at all)?

A couple of thoughts:

   1)	A full kernel with everything compiled in might not fit on boot media
	such as floppies, while modules allows you to not load stuff that isn't
	needed to until after the main booting is accomplished.

   2)	There are several devices that have multiple drivers (such as tulip,
	and old_tulip for example).  Which particular driver works depends on
	your exact particular hardware.  If both of these drivers are linked
	into the kernel, whatever the kernel chooses to initialize first will
	talk to the device.

   3)	Having drivers as modules means that you can remove them and reload
	them.  When I was working in an office, I had one scsi controller that
	was a different brand (Adaptec) than the main scsi controller (TekRam),
	and I hung a disk in a removable chasis on the scsi chain in addition
	to a tape driver and cd-rom.  When I was about to go home, I would copy
	all of the data to the disk, unmount it, and then unload the scsi
	device driver.  I would take the disk out, and reload the scsi device
	driver to get the tape/cd-rom.  I would then take the disk to my home
	computer.  I would reverse the process when I came in the morning.

   4)	If you have multiple scsi controllers of different brands, building on
	into the kernel and the other brand(s) as modules allows you to control
	which scsi controller is the first controller in terms of where the
	disks are.

-- 
Michael Meissner, Red Hat, Inc.  (GCC group)
PMB 198, 174 Littleton Road #3, Westford, Massachusetts 01886, USA
Work:	  meissner@redhat.com		phone: +1 978-486-9304
Non-work: meissner@spectacle-pond.org	fax:   +1 978-692-4482
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Re: The advantage of modules?

[Ookhoi]

Hi Michael,

> On Fri, Jan 05, 2001 at 10:50:20PM -0600, Evan Thompson wrote:
> > I'd like to know (I know, I'm being slightly off topic, while still
> > staying on topic, so I'm on topic...er...yes) if there is any
> > advantage, be it memory-wise or architectuarally wise, to use
> > modules?
> > 
> > I already know the obvious points of if you are creating a distro
> > that it is usually good to make a very modular kernel for those
> > wishing not to recompile their kernel, but I was wondering if there
> > were any other advantages to using modules vs. making a monolithic
> > kernel for a kernel to be used only on one machine (with no other
> > hardware support at all)?
> 
> A couple of thoughts:
> 
>    1)	A full kernel with everything compiled in might not fit on boot
>    media such as floppies, while modules allows you to not load stuff
>    that isn't needed to until after the main booting is accomplished.
> 
>    2)	There are several devices that have multiple drivers (such as
>    tulip, and old_tulip for example).  Which particular driver works
>    depends on your exact particular hardware.  If both of these
>    drivers are linked into the kernel, whatever the kernel chooses to
>    initialize first will talk to the device.
> 
>    3)	Having drivers as modules means that you can remove them and
>    reload them.  When I was working in an office, I had one scsi
>    controller that was a different brand (Adaptec) than the main scsi
>    controller (TekRam), and I hung a disk in a removable chasis on the
>    scsi chain in addition to a tape driver and cd-rom.  When I was
>    about to go home, I would copy all of the data to the disk, unmount
>    it, and then unload the scsi device driver.  I would take the disk
>    out, and reload the scsi device driver to get the tape/cd-rom.  I
>    would then take the disk to my home computer.  I would reverse the
>    process when I came in the morning.

You don't need modules for this to work.

		Ookhoi
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Re: The advantage of modules?

[Michael Meissner]

On Mon, Jan 08, 2001 at 07:26:01PM +0100, Ookhoi wrote:
> >    3)	Having drivers as modules means that you can remove them and
> >    reload them.  When I was working in an office, I had one scsi
> >    controller that was a different brand (Adaptec) than the main scsi
> >    controller (TekRam), and I hung a disk in a removable chasis on the
> >    scsi chain in addition to a tape driver and cd-rom.  When I was
> >    about to go home, I would copy all of the data to the disk, unmount
> >    it, and then unload the scsi device driver.  I would take the disk
> >    out, and reload the scsi device driver to get the tape/cd-rom.  I
> >    would then take the disk to my home computer.  I would reverse the
> >    process when I came in the morning.
> 
> You don't need modules for this to work.

Quoting from drivers/scsi/scsi.c:

	/*
	 * Usage: echo "scsi add-single-device 0 1 2 3" >/proc/scsi/scsi
	 * with  "0 1 2 3" replaced by your "Host Channel Id Lun".
	 * Consider this feature BETA.
	 *     CAUTION: This is not for hotplugging your peripherals. As
	 *     SCSI was not designed for this you could damage your
	 *     hardware !
	 * However perhaps it is legal to switch on an
	 * already connected device. It is perhaps not
	 * guaranteed this device doesn't corrupt an ongoing data transfer.
	 */

so my take is unless you explicitly use hotplug devices (I wasn't), that it is
much safer to unload the driver, unattach/attach scsi devices, and then reload
the driver (which will scan the scsi bus for devices), which you need modules
for.

-- 
Michael Meissner, Red Hat, Inc.  (GCC group)
PMB 198, 174 Littleton Road #3, Westford, Massachusetts 01886, USA
Work:	  meissner@redhat.com		phone: +1 978-486-9304
Non-work: meissner@spectacle-pond.org	fax:   +1 978-692-4482
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Re: The advantage of modules?

[Russell King]

Michael Meissner writes:
> Quoting from drivers/scsi/scsi.c:
> 
> 	/*
> 	 * Usage: echo "scsi add-single-device 0 1 2 3" >/proc/scsi/scsi
> 	 * with  "0 1 2 3" replaced by your "Host Channel Id Lun".
> 	 * Consider this feature BETA.
> 	 *     CAUTION: This is not for hotplugging your peripherals. As
> 	 *     SCSI was not designed for this you could damage your
> 	 *     hardware !
> 	 * However perhaps it is legal to switch on an
> 	 * already connected device. It is perhaps not
> 	 * guaranteed this device doesn't corrupt an ongoing data transfer.
> 	 */
> 
> so my take is unless you explicitly use hotplug devices (I wasn't), that
> it is much safer to unload the driver, unattach/attach scsi devices, and
> then reload the driver (which will scan the scsi bus for devices), which
> you need modules for.

I don't believe that is what it's trying to say.  There have been instances
in the past where unplugging a SCSI device from a powered on SCSI bus can
result in blown terminator power fuses and the like.  Whether this still
applies today, I don't know (are active terminators better or worse than
passive when it comes to this type of thing?)  However, what I do know is
the following, and I learnt it the hard way:

  I once had a machine and other stuff on a 4-way mains connector block
  that has been used for many years.  Unknown to me, the earth wire
  had become intermittent.  I was just about to connect another peripheral
  which was directly connected to the wall socket to this computer, and
  I happened to touch the connector body on both the peripheral and the
  computer.  I now know what a shock of >120V feels like.

Now, imagine what would happen if you connect a SCSI device, where this
condition exists, and the first thing that makes contact is the SCSI
databus.  Say goodbye to most, if not all devices on that SCSI bus.
   _____
  |_____| ------------------------------------------------- ---+---+-
  |   |         Russell King        rmk@arm.linux.org.uk      --- ---
  | | | | http://www.arm.linux.org.uk/personal/aboutme.html   /  /  |
  | +-+-+                                                     --- -+-
  /   |               THE developer of ARM Linux              |+| /|\
 /  | | |                                                     ---  |
    +-+-+ -------------------------------------------------  /\\\  |
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Re: The advantage of modules?

[Dan Hollis]

On Mon, 8 Jan 2001, Russell King wrote:
> > so my take is unless you explicitly use hotplug devices (I wasn't), that
> > it is much safer to unload the driver, unattach/attach scsi devices, and
> > then reload the driver (which will scan the scsi bus for devices), which
> > you need modules for.
> I don't believe that is what it's trying to say.  There have been instances
> in the past where unplugging a SCSI device from a powered on SCSI bus can
> result in blown terminator power fuses and the like.  Whether this still
> applies today, I don't know (are active terminators better or worse than
> passive when it comes to this type of thing?)

The term SCSI is depreciated as purely a physical layer. We talk SCSI over
many different physical layers (1394, usb, ata). Of course many of these
support hot plug natively.

You can get hotplug adapters for ata devices now. Can linux handle them?

-Dan

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Re: The advantage of modules?

[Russell King]

Dan Hollis writes:
> On Mon, 8 Jan 2001, Russell King wrote:
> > I don't believe that is what it's trying to say.  There have been instances
> > in the past where unplugging a SCSI device from a powered on SCSI bus can
> > result in blown terminator power fuses and the like.  Whether this still
> > applies today, I don't know (are active terminators better or worse than
> > passive when it comes to this type of thing?)
> 
> The term SCSI is depreciated as purely a physical layer. We talk SCSI over
> many different physical layers (1394, usb, ata). Of course many of these
> support hot plug natively.

And can you please explain how I can attach this USB Zip drive to this
50-wire SCSI bus please?  Or would you prefer me to call it a bus?
Something with 4 wheels maybe?  Maybe we should depreciate the term "bus"
as well just to remove that confusion. ;)

Seriously though, you can't depreciate a term for referring to a type of
bus without providing some other term to describe said bus.
   _____
  |_____| ------------------------------------------------- ---+---+-
  |   |         Russell King        rmk@arm.linux.org.uk      --- ---
  | | | | http://www.arm.linux.org.uk/personal/aboutme.html   /  /  |
  | +-+-+                                                     --- -+-
  /   |               THE developer of ARM Linux              |+| /|\
 /  | | |                                                     ---  |
    +-+-+ -------------------------------------------------  /\\\  |
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Re: The advantage of modules?

[Dan Hollis]

On Mon, 8 Jan 2001, Russell King wrote:
> Seriously though, you can't depreciate a term for referring to a type of
> bus without providing some other term to describe said bus.

You need to distinguish between SCSI-the-protocol and
SCSI-the-physical-layer. The term "SCSI" alone is simply too ambiguous to
be really useful anymore. I think you can use term "SCSI-1" or "SCSI-2"
when specicfally meaning SCSI protocol over classic 50 wire layer.

Saying "SCSI does not support hotplug" is very misleading.

Right now, the term "SCSI" is more akin to "IP".

-Dan

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Re: The advantage of modules?

[Richard B. Johnson]

On Mon, 8 Jan 2001, Dan Hollis wrote:

> On Mon, 8 Jan 2001, Russell King wrote:
> > Seriously though, you can't depreciate a term for referring to a type of
> > bus without providing some other term to describe said bus.
> 
> You need to distinguish between SCSI-the-protocol and
> SCSI-the-physical-layer. The term "SCSI" alone is simply too ambiguous to
> be really useful anymore. I think you can use term "SCSI-1" or "SCSI-2"
> when specicfally meaning SCSI protocol over classic 50 wire layer.
> 
> Saying "SCSI does not support hotplug" is very misleading.
> 
> Right now, the term "SCSI" is more akin to "IP".
> 
> -Dan

Err.... The American National Standard for information Systems, under
the American National Standards Institute, ANSI, approved a "Small
Computer System Interface" (SCSI) standard on June 23, 1986.

There have been many revisions, one of the last, called SCSI-2, was
approved on May 20, 1991. I used to sit on the committee. I have some
of the original drafts.

Although I haven't been involved for over 8 years, it us unlikely that
the word "SCSI" has been given up as some generic aspirin. SCSI still
means the stuff specified in the 519 Page document copyrighted by
ANSI, called "SMALL COMPUTER SYSTEM INTERFACE - 2", Dated May 20, 1991,
and the first draft released in June of 1986.

As such, you are not supposed to use the word SCSI to mean "control packet
interface" or whatever. It is supposed to refer to the hardware and
communications specifications (software), defined by the standard.
Although nobody is likely to haul is into court, we should not be using
SCSI to mean anything else.

And, SCSI does not "specify" hot-plug. It's just not covered in the
standard. However, you can certainly provide capabilities not covered
by a particular standard. It is some implementation details on how
SCSI (and other) devices are mounted, connected, disconnected, and
controlled that may allow hot-plugging.


Cheers,
Dick Johnson

Penguin : Linux version 2.4.0 on an i686 machine (799.54 BogoMips).

"Memory is like gasoline. You use it up when you are running. Of
course you get it all back when you reboot..."; Actual explanation
obtained from the Micro$oft help desk.


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Re: The advantage of modules?

[Alan Cox]

> Although I haven't been involved for over 8 years, it us unlikely that
> the word "SCSI" has been given up as some generic aspirin. SCSI still
> means the stuff specified in the 519 Page document copyrighted by
> ANSI, called "SMALL COMPUTER SYSTEM INTERFACE - 2", Dated May 20, 1991,
> and the first draft released in June of 1986.

SCSI nowdays is a message protocol. Its what powers fibrechannel at the high
end and ATAPI (IDE) and USB at the low end.

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