Merge strategy for klibc

Merge strategy for klibc

[H. Peter Anvin]

Okay, as of this point, I think klibc is in quite good shape; my
testing so far is showing that it can be used as a drop-in replacement
for the kernel root-mounting code.

That being said, there is guaranteed to be breakage, for two reasons:

a. There are several architectures which don't have klibc ports yet.
    Since I don't have access to them, I can't really do them, either.
    It's usually a matter of an afternoon or less to port klibc to a
    new architecture, though, if you have a working development
    environment for it.

b. There are a gajillion options in the way Linux handles its root
    filesystem.  I have tried to implement them all, but I haven't been
    able to test some of the more exotic conditions, mostly due to the
    fact that every boot environment I set up takes a *lot* of time and
    maintenance.  This has in fact been the by far the bulk of the time
    I've spent on klibc, not writing code.

Thus, it's not clear to me what particular approach makes most sense for 
pushing upstream.

1. Mechanism: the easiest for me would of course be git pull, but I'm 
certainly willing to break it up into patches or any other useful way.

A diff of by git tree from 2.6.16 gives:

   766 files changed, 84024 insertions(+), 3059 deletions(-)


2. State: the current git tree cleans up the arch-specific code for i386 
and x86-64; other architectures are going to need some minor cleanup in 
setup.c or the equvalent.

The current git tree includes a number of utilities, like dash (sh), 
which aren't used by the default kinit configuration.  Additionally, 
right now kinit is built monolitically, in other words there isn't a 
CONFIG_ option to turn off nfsmount, for example.

Again, I'm more than willing to put the tree in any particular state 
that makes sense.


3. Path: it probably would make sense to push this into -mm first?


It's taken this long, I'd like to make this actually happen...

	-hpa

Re: Merge strategy for klibc

[Jan-Benedict Glaw]

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On Mon, 2006-03-20 11:54:01 -0800, H. Peter Anvin <hpa@zytor.com> wrote:
> a. There are several architectures which don't have klibc ports yet.
>    Since I don't have access to them, I can't really do them, either.
>    It's usually a matter of an afternoon or less to port klibc to a
>    new architecture, though, if you have a working development
>    environment for it.

I haven't yet looked at your code, but what actually needs to be done?
Defining syscall macros?

I'd probably give it a try for VAX.

MfG, JBG

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Re: Merge strategy for klibc

[H. Peter Anvin]

Jan-Benedict Glaw wrote:
> 
> I haven't yet looked at your code, but what actually needs to be done?
> Defining syscall macros?
> 
> I'd probably give it a try for VAX.
> 

Each architecture needs an assembly stub generator for most syscalls, a 
crt0.S, plus adjustments for which syscalls are "special" (as in special 
ed) on that architecture.  There are also a couple of header files which 
need per-architecture configuration information.  All in all it is 
usually a few hours worth of work, no more.

	-hpa

Re: Merge strategy for klibc

[Al Viro]

On Mon, Mar 20, 2006 at 11:54:01AM -0800, H. Peter Anvin wrote:
> Okay, as of this point, I think klibc is in quite good shape; my
> testing so far is showing that it can be used as a drop-in replacement
> for the kernel root-mounting code.
> 
> That being said, there is guaranteed to be breakage, for two reasons:
> 
> a. There are several architectures which don't have klibc ports yet.
>    Since I don't have access to them, I can't really do them, either.
>    It's usually a matter of an afternoon or less to port klibc to a
>    new architecture, though, if you have a working development
>    environment for it.

Which ones?

Re: [klibc] Re: Merge strategy for klibc

[H. Peter Anvin]

Al Viro wrote:
> On Mon, Mar 20, 2006 at 11:54:01AM -0800, H. Peter Anvin wrote:
> 
>>Okay, as of this point, I think klibc is in quite good shape; my
>>testing so far is showing that it can be used as a drop-in replacement
>>for the kernel root-mounting code.
>>
>>That being said, there is guaranteed to be breakage, for two reasons:
>>
>>a. There are several architectures which don't have klibc ports yet.
>>   Since I don't have access to them, I can't really do them, either.
>>   It's usually a matter of an afternoon or less to port klibc to a
>>   new architecture, though, if you have a working development
>>   environment for it.
> 
> Which ones?
> 

This is the status of architectures in klibc, at least as far as I know.

Note that 64-bit architectures which have 32-bit fallback modes (e.g. 
MIPS) can use the 32-bit klibc if applicable.

    alpha:        Working
    arm-thumb:    Untested
    arm:          Working
    arm26:        Not yet ported
    cris:         Working
    h8300:        Not yet ported
    i386:         Working
    ia64:         Working
    m32r:         Untested
    m68k:         Not yet ported
    mips:         Working
    mips64:       Not yet ported
    parisc:       Working
    parisc64:     Not yet ported
    ppc:          Working
    ppc64:        Working
    s390:         Working static, shared untested
    s390x:        Working
    sh:           Untested
    sh64:         Not yet ported
    sparc:        Working
    sparc64:      Untested
    v850:         Not yet ported
    x86-64:       Working
    xtensa:       Not yet ported

	-hpa

Re: Merge strategy for klibc

[Ingo Oeser]

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Hi,

first thanks for your good work on that!

On Monday, 20. March 2006 20:54, H. Peter Anvin wrote:
> The current git tree includes a number of utilities, like dash (sh), 
> which aren't used by the default kinit configuration.

But its quite useful to be dropped into a shell, if anything goes wrong.
e.g. ubuntu assumes an modular kernel, which I don't like to have
and I got dropped into the shell quite often until all scripts worked as 
expected.

> Additionally,  
> right now kinit is built monolitically, in other words there isn't a 
> CONFIG_ option to turn off nfsmount, for example.

Yes, since after development of your init setup, you want to shrink it
as much as possible :-)

But all of this stuff is janitorial and can be done after merging the basic
ideas and completing the setup code move to user space.

Another idea is to still allow the current archive setups for initramfs,
because a static /dev might be best for embedded stuff where
you basically pre-compose a system image and download that to flash.

> 3. Path: it probably would make sense to push this into -mm first?

The usr/ part should go in ASAP, but please rip out the setup stuff 
only after a grace period announced in Documentation/feature-removal.txt
or sth. like that.


Regards

Ingo Oeser

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Re: Merge strategy for klibc

[Roman Zippel]

Hi,

On Mon, 20 Mar 2006, H. Peter Anvin wrote:

You forgot to provide any information (at least a summary) about what this 
is and how this will work. Please don't assume everyone is familiar with 
it.

There is one major question: how will this interface to distributions?

How can distributions add their own initializations and configurations or 
are they going to put an initrd on top of the kernel initrd? If this will 
have a kernel and a distribution part, it poses the question whether klibc 
has to be distributed with the kernel at all (a libc has a standard API 
after all) and the kernel just provides the kernel specific parts to 
whatever the distribution provides.

bye, Roman

Re: Merge strategy for klibc

[H. Peter Anvin]

Followup to:  <Pine.LNX.4.64.0603202228441.17704@scrub.home>
By author:    Roman Zippel <zippel@linux-m68k.org>
In newsgroup: linux.dev.kernel
> 
> You forgot to provide any information (at least a summary) about what this 
> is and how this will work. Please don't assume everyone is familiar with 
> it.
> 
> There is one major question: how will this interface to distributions?
> 
> How can distributions add their own initializations and configurations or 
> are they going to put an initrd on top of the kernel initrd? If this will 
> have a kernel and a distribution part, it poses the question whether klibc 
> has to be distributed with the kernel at all (a libc has a standard API 
> after all) and the kernel just provides the kernel specific parts to 
> whatever the distribution provides.
> 

Okay... quick summary (again)...

klibc is a small libc, small enough that it provides negible (or even
negative) overhead to bundle it inside the kernel binary.

The kernel tree part is there so that we can rip out in-kernel code
without breaking compatibility, or requiring a distribution-provided
initramfs.  In the future, we could consider retaining certain
binaries in the rootfs and have "on-demand userspace" by the kernel,
e.g. to do partition enumeration in userspace in a
backwards-compatible manner.

The default build provides a single binary called kinit, which is
(modulo any bugs) equivalent to the in-kernel root-mounting code, with
all its variants (initrd, nfsroot, load ramdisk from floppy, yadda
yadda.)  The existence of kinit allows the in-kernel code to be
removed without actually removing a feature.  Hence, the reason to put
this in the kernel tree is to make sure there is zero impact on
distributions.

If the distribution uses initramfs directly, kinit goes unused.  The
klibc code is also available as a standalone distribution, which at
least Ubuntu is currently using to build a custom initramfs.  Because
the kinit code is still userspace, it can share considerable amounts
of code with the standalone klibc utilities collection; in fact most
of the kinit pieces are available as standalone binaries which can be
weaved together by scripts or other C code.

The advantages of moving this code to userspace, thus is:

 - Simpler programming model (harder to screw up)
 - Easier to share code with distribution-customized setups
 - Code can be tested as standalone userspace binaries at runtime

A lot of the benefit is lost if, like now, there is a piece of code
which has to be written for kernel-mode programming, separate from
anything else and not testable except through a tedious kernel boot
cycle.

	-hpa

Re: Merge strategy for klibc

[Antonio Vargas]

On 3/22/06, H. Peter Anvin <hpa@zytor.com> wrote:
> Followup to:  <Pine.LNX.4.64.0603202228441.17704@scrub.home>
> By author:    Roman Zippel <zippel@linux-m68k.org>
> In newsgroup: linux.dev.kernel
> >
> > You forgot to provide any information (at least a summary) about what this
> > is and how this will work. Please don't assume everyone is familiar with
> > it.
> >
> > There is one major question: how will this interface to distributions?
> >
> > How can distributions add their own initializations and configurations or
> > are they going to put an initrd on top of the kernel initrd? If this will
> > have a kernel and a distribution part, it poses the question whether klibc
> > has to be distributed with the kernel at all (a libc has a standard API
> > after all) and the kernel just provides the kernel specific parts to
> > whatever the distribution provides.
> >
>
> Okay... quick summary (again)...
>
> klibc is a small libc, small enough that it provides negible (or even
> negative) overhead to bundle it inside the kernel binary.
>
> The kernel tree part is there so that we can rip out in-kernel code
> without breaking compatibility, or requiring a distribution-provided
> initramfs.  In the future, we could consider retaining certain
> binaries in the rootfs and have "on-demand userspace" by the kernel,
> e.g. to do partition enumeration in userspace in a
> backwards-compatible manner.
>
> The default build provides a single binary called kinit, which is
> (modulo any bugs) equivalent to the in-kernel root-mounting code, with
> all its variants (initrd, nfsroot, load ramdisk from floppy, yadda
> yadda.)  The existence of kinit allows the in-kernel code to be
> removed without actually removing a feature.  Hence, the reason to put
> this in the kernel tree is to make sure there is zero impact on
> distributions.
>
> If the distribution uses initramfs directly, kinit goes unused.  The
> klibc code is also available as a standalone distribution, which at
> least Ubuntu is currently using to build a custom initramfs.  Because
> the kinit code is still userspace, it can share considerable amounts
> of code with the standalone klibc utilities collection; in fact most
> of the kinit pieces are available as standalone binaries which can be
> weaved together by scripts or other C code.
>
> The advantages of moving this code to userspace, thus is:
>
>  - Simpler programming model (harder to screw up)
>  - Easier to share code with distribution-customized setups
>  - Code can be tested as standalone userspace binaries at runtime
>
> A lot of the benefit is lost if, like now, there is a piece of code
> which has to be written for kernel-mode programming, separate from
> anything else and not testable except through a tedious kernel boot
> cycle.
>
>         -hpa

ISTM that we are (finally? ;) moving piece by piece to a mixed
monolothic+microkenel, or rather that many of the things that were
first implemented in-kernel (on linux or other unixes) are being
slowly jettisoned to a kernel-provided userspace. All in all this is a
good step forward :)

Regarding helping test/develop this, is there any small distro already
using klibc for such purposes? Maybe you, hpa, could share you klibc
testing rig? This looks ripe for a qemu-based testing at the moment,
not being performance critical like many other current developments...

--
Greetz, Antonio Vargas aka winden of network

http://wind.codepixel.com/
windNOenSPAMntw@gmail.com
thesameasabove@amigascne.org

Every day, every year
you have to work
you have to study
you have to scene.

Re: Merge strategy for klibc

[H. Peter Anvin]

Antonio Vargas wrote:
> 
> Regarding helping test/develop this, is there any small distro already
> using klibc for such purposes? Maybe you, hpa, could share you klibc
> testing rig? This looks ripe for a qemu-based testing at the moment,
> not being performance critical like many other current developments...
> 

The klibc-integrated git tree is at:

git://git.kernel.org/pub/scm/linux/kernel/git/hpa/linux-2.6-klibc.git

At this point, the big thing is to drop this into as many 
weirdly-booting Linux setups as possible, and watch them hopefully have 
no effect whatsoever :)

For porting klibc, I have a set of tests which are also included. 
Unfortunately, they're not currently self-validating, which would be a 
significant enhancement.

	-hpa

Re: Merge strategy for klibc

[Michael Tokarev]

H. Peter Anvin wrote:
> Okay, as of this point, I think klibc is in quite good shape; my
> testing so far is showing that it can be used as a drop-in replacement
> for the kernel root-mounting code.
[]
> Thus, it's not clear to me what particular approach makes most sense for
> pushing upstream.

Why this needs to be "pushed" upstream in the first place?  Isn't it
simpler/easier/whatever to just require klibc to be present on the
build system for kernel?  If klibc is "sufficiently" independent of
the kernel (is it?  I see no reason it shouldn't), why it should go
with kernel?  Just point your CONFIG_INITRAMFS_SOURCE to some klibc
directory tree and be done with it, no need to distribute/build
klibc with kernel..

Thanks.

/mjt