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 From : Sergey Lentsov                       2:4615/71.10   12 Jan 2001  02:34:09
 To : All
 Subject : URL: http://lwn.net/2001/0111/kernel.php3
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    See also: [12]last week's Kernel page.
    
 Kernel development
 
    The current development kernel release is, well, actually, there is no
    development kernel release, and there will not be for some time (see
    below). Now that 2.4.0 is officially "stable," where is one to look
    for the bleeding edge? Options include 2.4.1, for which there is one
    prepatch release as of this writing. It is a very small patch which
    fixes problems seen by a few users. Those looking for something a
    little more adventurous will probably be more interested in Alan Cox's
    [13]2.4.0-ac5; he says: "Handle with care. I think the fs updates are
    right but I don't guarantee it." This patch contains an astounding
    number of fixes, many of which may wait some time before getting into
    2.4 proper.
    
    The current (other) stable kernel release is 2.2.18. The 2.2.19
    prepatch is up to [14]2.2.19pre7.
    
    Alan Cox has [15]announced a new policy for 2.2 updates. From this
    point on, updates to drivers will only be accepted if the same update
    is also available for 2.4.
    
    The current ancient kernel release is 2.0.39, which was [16]announced
    on January 9. This release was long in coming, and will probably be
    the last in the 2.0 series.
    
    2.4.0 is out - now what? There is no shortage of kernel developers
    (and users) who are ready for the end of the 2.4 feature freeze and
    the beginning of a new development series. Some patience will yet be
    required, however; Linus doesn't expect to start accepting patches
    until well into the (northern hemisphere) Spring.
    
    In fact, he doesn't even want to see a whole lot of bugfix patches.
    [17]This posting went out to describe Linus's approach to 2.4 patches:
    
      In short, releasing 2.4.0 does not open up the floor to just about
      anything. In fact, to some degree it will probably make patches
      _less_ likely to be accepted than before, at least for a while. I
      want to be absolutely convinced that the basic 2.4.x infrastructure
      is solid as a rock before starting to accept more involved patches.
      
    The purpose here is to try to get away from a pattern seen with other
    stable kernels, where stability actually goes down for the first few
    minor releases. So, this time around, only the most important stuff
    will go in.
    
    There will also be no development series until 2.4 is truly wrapped up
    and passed on to another maintainer. Linus expects that, as with
    previous stable kernels, that will not happen for about four months.
    Says Linus: "In short, I'm hoping for a fairly boring next few months.
    The more boring, the better."
    
    Zero-copy networking. Some developers are not content with a boring
    existence, and have started putting out interesting patches for future
    development kernels. Perhaps the most interesting is [18]David
    Miller's zero-copy networking patch, which promises to greatly
    increase the performance of the Linux networking subsystem - which is
    already fast.
    
    Networking in Linux currently involves, at a minimum, copying all data
    between the kernel and the user process which produces or consumes it.
    Copying data takes time, of course; it also can clog up the CPU memory
    cache with useless data. What the zero-copy patch does is attempt to
    move network data directly between user-space memory and the network
    interface whenever possible. Such data never passes through the cache
    and need not be copied by the processor.
    
    This patch is a "proof of concept" release; it is not being proposed
    for inclusion in its current form. Instead, the idea is to get the
    peer review process going, see what sort of performance improvements
    really result, and find the problems. The initial indications are
    good; [19]according to Ingo Molnar, "We can saturate a gigabit link
    with TCP traffic, at about 20% CPU usage on a 500 MHz x86 UP system."
    
    The implementation itself is a bit controversial, however. To do
    zero-copy I/O, the kernel must locate and lock the user process's data
    in physical memory. Stephen Tweedie's "kiobuf" infrastructure was
    developed to handle this task for the raw block I/O subsystem, but the
    zero-copy networking patch does not use kiobufs. Instead, the
    developers chose to implement their own subsystem which handles these
    tasks.
    
    Their reasoning is that the kiobuf structure is far too heavy for the
    needs of the networking code. Network connections are quick, numerous,
    and transient; the code that handles them also needs to be light and
    fast. The networking developers concluded that kiobufs did not meet
    these needs; so they went off and created something they liked better.
    
    In the resulting discussion it turns out that [20]Linus does not like
    the kiobuf interface:
    
      And kiobufs can rot in hell for their design mistakes. Maybe
      somebody will listen some day and fix them up, and in the meantime
      they can look at the networking code for an example of how to do
      it.
      
    Given the source, this suggests that the kiobuf interface will likely
    see some major changes in the 2.5 development series, once it gets
    going. (Note that there is also [21]an updated zero-copy patch for the
    2.4.1pre1 kernel available).
    
    Security trouble with ReiserFS? A potential security problem with
    ReiserFS was [22]reported this week. It seems that a buffer overrun
    problem exists, sometimes, when a directory with an exceptionally long
    name is created. Not everybody has been able to reproduce the problem,
    however.
    
    The source of the bug has not been positively identified as of this
    writing. It appears, however, that it may be in the virtual filesystem
    code, rather than in ReiserFS itself. A definitive fix is thus not
    available at this time. Chris Mason has released quick and dirty
    patches (which simply disable long directory names) for [23]ReiserFS
    3.5 and [24]3.6. Those who are especially worried about this problem
    may want to apply one or the other of the patches to close the
    vulnerability for now.
    
    Other patches and updates released this week include:
    
      * Tim Fraser has released [25]LOMAC v1.0, a mandatory access control
        implementation for the 2.2 kernel.
      * [26]ext3-0.0.5e was released by Stephen Tweedie. He is getting
        toward the end of this phase of development for the ext3
        journaling filesystem; it will soon go into a code freeze prior to
        the 1.0 release.
      * Ludovic Fernandez at Sun has [27]released a patch (i386 only)
        which makes the Linux kernel preemptable.
      * A number of "make it work with 2.4.0" patches have come out,
        including [28]reiserfs (Chris Mason); [29]modutils, [30]ksymoops
        and [31]kdb (all from Keith Owens); [32]user-mode Linux (Jeff
        Dike); [33]stackguard (Greg KH); [34]the m68K port (Geert
        Uytterhoeven); [35]uClinux (Jeff Dionne); [36]CML2 (Eric Raymond);
        [37]Linux Intrusion Detection System (Huagang Xie); and
        [38]international crypto (Alexander Kjeldaas - see [39]this update
        for the correct download location).
      * Matthias Juchem has posted [40]a bug report script for inclusion
        with the kernel. It has drawn complaints, though, due to the fact
        that it is written in Perl, which is not currently required by
        anything in the kernel distribution.
      * Greg KH has [41]announced a new mailing list for developers of
        hotplug functionality in the kernel.
      * [42]Oprofile, an instruction-grain kernel profiler, has been
        released by John Levon.
      * [43]Netfilter 1.2 has been released by Rusty Russell.
        
    Section Editor: [44]Jonathan Corbet
    January 11, 2001
    
    For other kernel news, see:
      * [45]Kernelnotes
      * [46]Kernel traffic
      * [47]Kernel Newsflash
      * [48]Kernel Trap
    
    Other resources:
      * [49]Kernel Source Reference
      * [50]L-K mailing list FAQ
      * [51]Linux-MM
      * [52]Linux Scalability Project
    
    
    
                                                   [53]Next: Distributions
    
    [54]Eklektix, Inc. Linux powered! Copyright Щ 2001 [55]Eklektix, Inc.,
    all rights reserved
    Linux Ю is a registered trademark of Linus Torvalds
 
 References
 
    1. http://lwn.net/
    2. http://ads.tucows.com/click.ng/pageid=132-000-001-001
    3. http://lwn.net/2001/0111/
    4. http://lwn.net/2001/0111/security.php3
    5. http://lwn.net/2001/0111/dists.php3
    6. http://lwn.net/2001/0111/devel.php3
    7. http://lwn.net/2001/0111/commerce.php3
    8. http://lwn.net/2001/0111/press.php3
    9. http://lwn.net/2001/0111/announce.php3
   10. http://lwn.net/2001/0111/backpage.php3
   11. http://lwn.net/2001/0111/bigpage.php3
   12. http://lwn.net/2001/0104/kernel.php3
   13. http://lwn.net/2001/0111/a/2.4.0-ac5.php3
   14. http://lwn.net/2001/0111/a/2.2.19pre7.php3
   15. http://lwn.net/2001/0111/a/2.2-policy.php3
   16. http://lwn.net/2001/0111/a/2.0.39.php3
   17. http://lwn.net/2001/0111/a/lt-2.4-policy.php3
   18. http://lwn.net/2001/0111/a/zero-copy.php3
   19. http://lwn.net/2001/0111/a/im-zero-copy.php3
   20. http://lwn.net/2001/0111/a/lt-kiobuf.php3
   21. http://lwn.net/2001/0111/a/zero-copy-2.php3
   22. http://lwn.net/2001/0111/a/reiserfs-bug.php3
   23. http://lwn.net/2001/0111/a/reiserfs-fix-3.5.php3
   24. http://lwn.net/2001/0111/a/reiserfs-fix-3.6.php3
   25. http://lwn.net/2001/0111/a/lomac.php3
   26. http://lwn.net/2001/0111/a/ext3.php3
   27. http://lwn.net/2001/0111/a/preemptive.php3
   28. http://lwn.net/2001/0111/a/reiserfs.php3
   29. http://lwn.net/2001/0111/a/modutils.php3
   30. http://lwn.net/2001/0111/a/ksymoops.php3
   31. http://lwn.net/2001/0111/a/kdb.php3
   32. http://lwn.net/2001/0111/a/user-mode.php3
   33. http://lwn.net/2001/0111/a/stackguard.php3
   34. http://lwn.net/2001/0111/a/m68k.php3
   35. http://lwn.net/2001/0111/a/uclinux.php3
   36. http://lwn.net/2001/0111/a/cml.php3
   37. http://lwn.net/2001/0111/a/lids.php3
   38. http://lwn.net/2001/0111/a/kerneli.php3
   39. http://lwn.net/2001/0111/a/kerneli2.php3
   40. http://lwn.net/2001/0111/a/bug-report.php3
   41. http://lwn.net/2001/0111/a/hotplug.php3
   42. http://lwn.net/2001/0111/a/oprofile.php3
   43. http://lwn.net/2001/0111/a/netfilter-1.2.php3
   44. mailto:lwn@lwn.net
   45. http://www.kernelnotes.org/
   46. http://kt.linuxcare.com/
   47. http://www.atnf.csiro.au/~rgooch/linux/docs/kernel-newsflash.html
   48. http://www.kerneltrap.com/
   49. http://lksr.org/
   50. http://www.tux.org/lkml/
   51. http://www.linux.eu.org/Linux-MM/
   52. http://www.citi.umich.edu/projects/linux-scalability/
   53. http://lwn.net/2001/0111/dists.php3
   54. http://www.eklektix.com/
   55. http://www.eklektix.com/
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