Groups > linux.kernel > #1261950

Re: [RFC PATCH 00/28] Linux Kernel Library

From	Octavian Purdila <octavian.purdila@intel.com>
Newsgroups	linux.kernel
Subject	Re: [RFC PATCH 00/28] Linux Kernel Library
Date	2015-11-04 00:10 +0100
Message-ID	<qqSSe-O3-23@gated-at.bofh.it> (permalink)
References	<qqQnn-7AN-3@gated-at.bofh.it> <qqRCO-8it-1@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Tue, Nov 3, 2015 at 11:40 PM, Richard Weinberger
<richard.weinberger@gmail.com> wrote:

Hi Richard,

> On Tue, Nov 3, 2015 at 9:20 PM, Octavian Purdila
> <octavian.purdila@intel.com> wrote:
>> LKL (Linux Kernel Library) is aiming to allow reusing the Linux kernel code
>> as extensively as possible with minimal effort and reduced maintenance
>> overhead.
>>
>> Examples of how LKL can be used are: creating userspace applications
>> (running on Linux and other operating systems) that can read or write Linux
>> filesystems or can use the Linux networking stack, creating kernel drivers
>> for other operating systems that can read Linux filesystems, bootloaders
>> support for reading/writing Linux filesystems, etc.
>>
>> With LKL, the kernel code is compiled into an object file that can be
>> directly linked by applications. The API offered by LKL is based on the
>> Linux system call interface.
>>
>> LKL is implemented as an architecture port in arch/lkl. It relies on host
>> operations defined by the application or a host library (tools/lkl/lib).
>>
>> The latest LKL version can be found at git@github.com:lkl/linux.git
>
> Or more copy&paste friendly: https://github.com/lkl/linux.git
>
>> FAQ
>> ===
>>
>> Q: How is LKL different from UML?
>> A: UML provides a full OS environment (e.g. user/kernel separation, user
>> processes) and also has requirements (a filesystem, processes, etc.) that
>> makes it hard to use it for standalone applications. UML also relies
>> heavily on Linux hosts. On the other hand LKL is designed to be linked
>> directly with the application and hence does not have user/kernel
>> separation which makes it easier to use it in standalone applications.
>
> So, this is a "liblinux" where applications are directly linked
> against the kernel.
> IOW system calls are plain function calls into the kernel?
>

More like "thread" calls. All system calls are executed in a dedicate
(kernel) thread to avoid race conditions with the "interrupt" path.

> This eliminates UML's most problematic areas, system call handling via ptrace()
> and virtual memory management via SIGSEGV. :-)
>

:)

>> Q: How is LKL different from LibOS?
>> A: LibOS re-implements high-level kernel APIs for timers, softirqs,
>> scheduling, sysctl, SLAB/SLUB, etc. LKL behaves like any arch port,
>> implementing the arch level operations requested by the Linux kernel. LKL
>> also offers a host interface so that support for multiple hosts can be
>> easily implemented.
>
> Yeah, these re-implementations are what I find most worrisome about LibOS.
>
>>
>> Building LKL the host library and LKL applications
>> ==================================================
>>
>> % cd tools/lkl
>> % make
>>
>> will build LKL as a object file, it will install it in tools/lkl/lib together
>> with the headers files in tools/lkl/include then will build the host library,
>> tests and a few of application examples:
>>
>> * tests/boot - a simple applications that uses LKL and exercises the basic
>> LKL APIs
>>
>> * fs2tar - a tool that converts a filesystem image to a tar archive
>>
>> * cptofs/cpfromfs - a tool that copies files to/from a filesystem image
>
> Seeing forward to have a libguestfs port. :-)
>
> Is LKL strictly single threaded?
>

At this point yes. SMP support is on my todo list though :)
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Thread

[RFC PATCH 00/28] Linux Kernel Library Octavian Purdila <octavian.purdila@intel.com> - 2015-11-03 21:30 +0100
  [RFC PATCH 21/28] lkl tools: host lib: posix host operations Octavian Purdila <octavian.purdila@intel.com> - 2015-11-03 21:30 +0100
    Re: [RFC PATCH 21/28] lkl tools: host lib: posix host operations Arnd Bergmann <arnd@arndb.de> - 2015-11-08 00:20 +0100
      Re: [RFC PATCH 21/28] lkl tools: host lib: posix host operations Octavian Purdila <octavian.purdila@intel.com> - 2015-11-08 05:10 +0100
        Re: [RFC PATCH 21/28] lkl tools: host lib: posix host operations Arnd Bergmann <arnd@arndb.de> - 2015-11-08 11:40 +0100
  [RFC PATCH 18/28] lkl tools: host lib: virtio devices Octavian Purdila <octavian.purdila@intel.com> - 2015-11-03 21:30 +0100
  [RFC PATCH 19/28] lkl tools: host lib: virtio block device Octavian Purdila <octavian.purdila@intel.com> - 2015-11-03 21:30 +0100
    Re: [RFC PATCH 19/28] lkl tools: host lib: virtio block device Richard Weinberger <richard.weinberger@gmail.com> - 2015-11-07 13:30 +0100
      Re: [RFC PATCH 19/28] lkl tools: host lib: virtio block device Octavian Purdila <octavian.purdila@intel.com> - 2015-11-08 05:20 +0100
        Re: [RFC PATCH 19/28] lkl tools: host lib: virtio block device Richard Weinberger <richard@nod.at> - 2015-11-08 14:40 +0100
  [RFC PATCH 13/28] lkl: initialization and cleanup Octavian Purdila <octavian.purdila@intel.com> - 2015-11-03 21:30 +0100
  [RFC PATCH 20/28] lkl tools: host lib: filesystem helpers Octavian Purdila <octavian.purdila@intel.com> - 2015-11-03 21:30 +0100
  [RFC PATCH 24/28] lkl tools: tool that reads/writes to/from a filesystem image Octavian Purdila <octavian.purdila@intel.com> - 2015-11-03 21:30 +0100
  [RFC PATCH 22/28] lkl tools: "boot" test Octavian Purdila <octavian.purdila@intel.com> - 2015-11-03 21:30 +0100
  [RFC PATCH 02/28] kbuild: allow architectures to automatically define kconfig symbols Octavian Purdila <octavian.purdila@intel.com> - 2015-11-03 21:30 +0100
  [RFC PATCH 17/28] lkl tools: host lib: memory mapped I/O helpers Octavian Purdila <octavian.purdila@intel.com> - 2015-11-03 21:30 +0100
  [RFC PATCH 28/28] lkl tools: add support for Windows host Octavian Purdila <octavian.purdila@intel.com> - 2015-11-03 21:30 +0100
  [RFC PATCH 09/28] lkl: timers, time and delay support Octavian Purdila <octavian.purdila@intel.com> - 2015-11-03 21:30 +0100
  [RFC PATCH 16/28] lkl tools: host lib: add lkl_strerror and lkl_printf Octavian Purdila <octavian.purdila@intel.com> - 2015-11-03 21:30 +0100
  [RFC PATCH 01/28] asm-generic: atomic64: allow using generic atomic64 on 64bit platforms Octavian Purdila <octavian.purdila@intel.com> - 2015-11-03 21:40 +0100
  [RFC PATCH 04/28] lkl: host interface Octavian Purdila <octavian.purdila@intel.com> - 2015-11-03 21:40 +0100
    Re: [RFC PATCH 04/28] lkl: host interface Hajime Tazaki <thehajime@gmail.com> - 2015-11-04 00:40 +0100
  [RFC PATCH 05/28] lkl: memory handling Octavian Purdila <octavian.purdila@intel.com> - 2015-11-03 21:40 +0100
  [RFC PATCH 07/28] lkl: interrupt support Octavian Purdila <octavian.purdila@intel.com> - 2015-11-03 21:40 +0100
  [RFC PATCH 06/28] lkl: kernel threads support Octavian Purdila <octavian.purdila@intel.com> - 2015-11-03 21:40 +0100
  [RFC PATCH 03/28] lkl: architecture skeleton for Linux kernel library Octavian Purdila <octavian.purdila@intel.com> - 2015-11-03 21:40 +0100
  Re: [RFC PATCH 00/28] Linux Kernel Library Richard Weinberger <richard.weinberger@gmail.com> - 2015-11-03 22:50 +0100
    Re: [RFC PATCH 00/28] Linux Kernel Library "Richard W.M. Jones" <rjones@redhat.com> - 2015-11-03 23:50 +0100
      Re: [RFC PATCH 00/28] Linux Kernel Library Octavian Purdila <octavian.purdila@intel.com> - 2015-11-04 00:30 +0100
        Re: [RFC PATCH 00/28] Linux Kernel Library Austin S Hemmelgarn <ahferroin7@gmail.com> - 2015-11-04 14:30 +0100
        Re: [RFC PATCH 00/28] Linux Kernel Library "Richard W.M. Jones" <rjones@redhat.com> - 2015-11-04 15:00 +0100
          Re: [RFC PATCH 00/28] Linux Kernel Library Octavian Purdila <octavian.purdila@intel.com> - 2015-11-04 15:30 +0100
            Re: [RFC PATCH 00/28] Linux Kernel Library Richard Weinberger <richard@nod.at> - 2015-11-07 01:40 +0100
              Re: [RFC PATCH 00/28] Linux Kernel Library "Richard W.M. Jones" <rjones@redhat.com> - 2015-11-07 08:20 +0100
              Re: [RFC PATCH 00/28] Linux Kernel Library "Richard W.M. Jones" <rjones@redhat.com> - 2015-11-07 11:50 +0100
                Re: [RFC PATCH 00/28] Linux Kernel Library Octavian Purdila <octavian.purdila@intel.com> - 2015-11-09 17:40 +0100
              Re: [RFC PATCH 00/28] Linux Kernel Library Octavian Purdila <octavian.purdila@intel.com> - 2015-11-08 05:20 +0100
              Re: [RFC PATCH 00/28] Linux Kernel Library Octavian Purdila <octavian.purdila@intel.com> - 2015-11-08 05:40 +0100
      Re: [RFC PATCH 00/28] Linux Kernel Library Hajime Tazaki <thehajime@gmail.com> - 2015-11-04 00:30 +0100
    Re: [RFC PATCH 00/28] Linux Kernel Library Octavian Purdila <octavian.purdila@intel.com> - 2015-11-04 00:10 +0100
      Re: [RFC PATCH 00/28] Linux Kernel Library Octavian Purdila <octavian.purdila@intel.com> - 2015-11-09 16:20 +0100
  Re: [RFC PATCH 00/28] Linux Kernel Library Hajime Tazaki <thehajime@gmail.com> - 2015-11-08 14:50 +0100

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