ANNOUNCE: User-space System Device Enumation (uSDE)

-----Original Message-----
From: [email protected] [mailto:[email protected]]On Behalf Of Greg KH
Sent: Wednesday, October 29, 2003 6:44 AM
To: Steven Dake
Cc: Lars Marowsky-Bree; Mark Bellon; [email protected]; [email protected]; [email protected]
Subject: Re: ANNOUNCE: User-space System Device Enumation (uSDE)

Quoted 5 lines · Steven Dake

Quoted 4 lines · Lars Marowsky-Bree

Quoted 1 line · Mark Bellon

The uSDE and udev are simlar in some respects. The uSDE

allows for

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complete control of the policy handling a device - not

just its naming.

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Well, so could udev in theory, and I had this plan to

enhance it to do

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so for the specific case of multipathing one day in the

not too distant

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future (ie, before q1/04).

In as far as I can see, udev and uSDE really do not have

too different

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goals. Competition is good, but only if they explore

distinct approaches

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;-)

There are several distinct approaches which have been enumerated in other mails.

Since this point has not been addressed, I'd like to focus

on the major

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difference in philosophy.

SDE places all policy in the hands of the policy developer

in a seperate

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policy program. udev places the policies in the main

processing loop of

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the system, effectively implementing whatever policy is

desired by the

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udev maintainers.

What do you mean by "policy"?

If you are saying that SDE allows programmers the ability to write new programs to plug into your framework to create new types of policies, then I understand that. Your loadable plugins look like they support that. But they require a dynamic loader :)

What udev is doing is trying to provide a flexible policy that will work
for everyone, with a heirchy of rules that can be easily controlled and
changed by anyone who can operate a text editor (and soon to be changed
by GUI applications, like the HAL project).

I have not heard of any situation in which the current udev set of rules
do not work out for them. And if you can think of one, can't it be covered by the CALLOUT rule? For example, someone has sent me a small userspace program that works with the CALLOUT rule that handles multipath devices by talking to the dm code. Now that's pretty flexible.

If you (or anyone else) thinks of something that the existing udev rules
do not handle, please let me know. If it's too complex, then yes, the user should use write their own SDE plugin. But remember, 99.9% of the
people out there just want the LSB device names, with possibly a persistent entry for their digital camera and USB joystick, which udev handles just fine today.

For people with 4000 real scsi disks, udev also works well. That seems
to cover the wide range of users.

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Without seperating policies from the core executive of device naming system, the core of udev suffers from the same issues as

placing policy

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in the kernel suffers. Lack of maintainability, lack of

user-defined

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functionality, bloat, etc.

Easy Separation? Hm, in looking at udev, if you just replace 2 .c files
with your new naming scheme, everything works just fine.

And if you want to go down the path of accusations about lack of maintainability, bloat, etc. I will be glad to point people at your tree
and then they can see these kinds of numbers:

For SDE:

$ find . -type f | egrep '[.c|.h]$' | xargs wc -l | tail -1
  57328 total

Wow, you build 18 shared libraries:

$ find . -type f | grep '\.so' | wc
     18      18     625

For udev:

$ find . -type f | egrep '[.c|.h]$' | xargs wc -l | tail -1
  17632 total

And that includes all of klibc, which really is not fair for udev to calculate. So let's just look at the udev code size:

$ ls | egrep '[.c|.h]$' | xargs wc -l | tail -1
   2613 total

And to be complete, let's add the totals of libsysfs and tdb, but to be
fair any udev developer never has to look into those files:

libsysfs is this big:

   3798 total

And tdb is this big:

   2679 total

So adding those numbers up we get these kinds of numbers for size of the
.c and .h files in the different projects:

    SDE:  57328 lines
    udev:  9090 lines

That makes SDE over 6 times bigger in source code alone than all of udev (including tdb and libsysfs).

I can compare executable size too, if you really want to still claim that udev is suffering from "lack of maintainability and bloat" if you really want :)

Oh, any reason you all haven't shown a working uSDE system in public anywhere?

thanks,

greg k-h

p.s. yes, I know lines of code is a horrible metric, and doesn't really
mean squat. I just want to point out the huge size difference between the current state of udev and SDE, with pretty much identical functionality from what I can tell.

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Quoted 3 lines

From a pure technical point of view and from presentations made by the

authors of u*** perspective
i think uSDE could add some interresting features like a customizable naming policy.

For instance: geographical addressing to identify devices using rack, subrack, slot numbers seems possible.

In the interest of full disclosure, Min is one of the SDE authors, and I am one of the udev authors.

Min, maybe you can answer why Intel has spent effort on this project instead of offering to help udev, which has been public for a long time now?

In the past we experimented with udev, and even did a little work on sysfsutils (which I though udev was using, but looking at udev-005 I still see the libsysfs directory.)

I see the the TODO list in udev-005. Are all these items wide open, or have people already spoken for some parts? Maybe you have a couple of items you consider higher priority?