Is L4Linux can use its existed Linux driver to access hardware device?

[Matthias Lange]

Hi,

On 09/07/2016 09:00 AM, Zhe Zhao wrote:
> Hi,
> 
> Thanks for you answers.
> 
> Does Fiasco use the scheduler that follow the priority? I mean like if
> there is high priority task, it will always have CPU?

I would like to point you to this recent thread on the mailing list
which discusses details about L4Re's scheduling [1].

> Does Fiasco already support tickless kernel? or it will use a fixed 1000
> HZ as the tick?

There is some support for tickless/oneshot mode in the L4Re microkernel
but it is not tested.

> I'd like to run L4Linux on a Droid-xu4 or raspberry is there any easy
> start guide for it?

Unfortunately no. But it is not complicated either. You can take the
L4Linux basic example as a starting point. You need to build the L4Re
microkernel for the right platform. The userland needs to be compiled
for the right ARM architecture (Rasperry Pi is ARM6k whereas the Droid
is ARMv7). Then you create an uImage which you can e.g. boot via tftp.

> When I tried the L4Linux with ramdisk which in the L4Re snapshot, it
> seems the it just like running a Linux. I don't know if below
> understanding is correct, if not please correct me
> 
> The syscall fork "int 80" will be redirect to L4Linux from Fiasco by IPC
> (how Fiasco knows to redirect int 80 through IPC to L4Linux?), and fork
> will be executed inside L4Linux, then L4Linux will create Fiasco task?
>  (so here we have two task proc combined to identify one linux process),
> and L4Linux will create vmspace for the process ? then how the memory
> space be handled to Fiasco?

L4-like systems have the concept of an exception handler per thread. For
L4Linux this means that all exceptions triggered by a Linux user process
are send to the L4Linux kernel.

In the case of fork() the L4Linux kernel eventually creates a new L4
task (l4_factory_create_task). Memory gets mapped from the L4Linux task
into the new task e.g. upon pagefaults.

> From the above assumption, it means I can just build a rootfs with
> native Linux apps, and use IO manager to pass the harddisk/emmc to
> L4Linux, then I can run whatever apps I like?

Basically yes. On ARM platforms there are some stumbling blocks for sure
as device pass-through can be tricky at times.

> I'd like to start read codes related to Fiasco, L4Re, any suggestions
> about the start point?

That's a very generic question and the generic answer for the L4Re
microkernel is: fiasco/src/kern. Do you have any specific mechanisms in
mind you want to understand?

Matthias.


[1] http://os.inf.tu-dresden.de/pipermail/l4-hackers/2016/007907.html

> 
> Br
> Alex
> 
> 
> 2016-09-06 23:37 GMT+08:00 Matthias Lange
> <matthias.lange at kernkonzept.com <mailto:matthias.lange at kernkonzept.com>>:
> 
>     Hi,
> 
>     On 09/05/2016 11:36 AM, Zhe Zhao wrote:
>     > Hi,
>     >
>     > Thanks for your answers, I really appreciate it.
>     >
>     > I tried to run L4Linux and L4Re in a qemu environment, is it support SMP
>     > already? I found I only have a single core L4Linux running. and Fiasco
>     > report only one scheduler instance.
> 
>     Yes, SMP is supported. Have you configured the L4Re microkernel with
>     multiprocessing support? Did you start qemu with multiple CPUs? To
>     enable more CPUs in L4Linux you need to pass the 'l4x_cpus=<VALUE>'
>     parameter on the cmdline.
> 
>     > And is it possible to direct reuse the L4Linux's driver instead of
>     > rewrite them in L4Re? is that IO manager used to mapping all needed
>     > device physical address to L4Linux's memory space? Is that mean I can map
>     > all device direct to L4Linux through IO manager?
> 
>     Yes, but there might be work involved. First you should make yourself
>     familiar with the concepts of Io [0].
> 
>     > Is there any work ongoing to support ARM64 on L4Re and L4Linux? It will
>     > be quite interesting consider most of the ARM device are moving to be 64
>     > bit arch.
> 
>     We are looking at it but there is nothing to announce publicly right now
> 
>     > Do you have some recommend documents for the newbie like me to get a
>     > quick start up?
> 
>     The L4Re documentation [1].
> 
> 
>     Matthias.
> 
>     [0] http://l4re.org/doc/io.html
>     [1] http://l4re.org/doc/
> 
>     > Br
>     > Alex
>     >
>     > 2016-09-02 14:24 GMT+08:00 Matthias Lange
>     > <matthias.lange at kernkonzept.com
>     <mailto:matthias.lange at kernkonzept.com>
>     <mailto:matthias.lange at kernkonzept.com
>     <mailto:matthias.lange at kernkonzept.com>>>:
>     >
>     >     Hi,
>     >
>     >     On 08/31/2016 02:35 PM, Zhe Zhao wrote:
>     >     > Hi,
>     >     >
>     >     > After read the basic ideas of L4Linux I have some questions
>     related to it.
>     >     >
>     >     > Is L4Linux run as a paravirtualization VM on L4Re? Then the
>     traditional
>     >     > Linux Process just still compiled against Linux system and
>     put them
>     >     > together with L4Linux disk image?
>     >     > so it means L4Re works like qemu and Linuxl?
>     >
>     >     No, L4Re does not work like qemu.
>     >
>     >     > or L4Re works as a micro kernel operating system, and
>     L4Linux run as a
>     >     > process on it, all devices handled to L4Linux to reuse the
>     drivers of
>     >     > L4Linux? and the previous Linux process
>     >     > compiled with Linux, but run direct on L4Re as L4 processes
>     which
>     >     > communicate with L4Linux through IPC?
>     >
>     >     L4Linux is a modified version of the Linux kernel with the
>     hardware
>     >     abstraction layer (HAL) implemented using L4Re primitives.
>     Technically
>     >     L4Re appears to be "just" another hardware architecture for
>     the Linux
>     >     kernel, just like ARM or MIPS.
>     >
>     >     L4Linux runs as a user space task on top of the L4Re
>     microkernel and at
>     >     the (Linux) kernel ABI is unmodified which allows to run
>     existing Linux
>     >     programs. That means, you can compile "normal" Linux programs
>     with your
>     >     standard tool chain, put the binary onto a ramdisk or disk
>     image and run
>     >     it with L4Linux.
>     >
>     >     > it is quite confused after read a little of the codes, in
>     L4Linux, seems
>     >     > there is some injection of L4 task stuffs inside
>     thread_struct of Linux,
>     >     > but also have some vCPU related stuffs,
>     >     > can you help me about what is the real behavior of L4Linux?
>     >
>     >     Each (Linux) process is actually an L4Re task with the
>     exception and
>     >     page fault handler set to the L4Linux task. That's why some
>     L4-specific
>     >     additions are required to Linux kernel data structures.
>     >
>     >     Matthias.
>     >
>     >     > I'm sorry to ask this basic questions, but after some
>     digging I feel
>     >     > quite confused about how it works.