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 From : Sergey Lentsov                       2:4615/71.10   13 Sep 2001  16:25:19
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 Subject : URL: http://www.lwn.net/2001/0913/kernel.php3
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    See also: [14]last week's Kernel page.
    
 Kernel development
 
    The current kernel release is still 2.4.9. Linus is currently up to
    [15]2.4.10-pre8, which includes a note from him that appears to settle
    the min/max issue for now. Prior to that was [16]2.4.10-pre7, a
    relatively large patch which included a great deal of stuff merged in
    from the "ac" series. Linus has [17]suggested (scroll to the bottom)
    that, once the merge with Alan is complete, the 2.5 series will begin:
    
      It still sounds very much like a 2.5.x thing (and hopefully I and
      Alan can merge enough that it's going to be RSN), but if done right
      it should be trivial to back-port to 2.4.x after testing.
      
    Alan, meanwhile, is not standing still; his latest is [18]2.4.9-ac10.
    Among other things, Alan is [19]claiming far better virtual memory
    performance for his kernels. Users of "ac" kernels, it seems, do not
    have to put up with the "living out of swap" feeling of the Linus
    series...
    
    Alan also released [20]2.2.20pre10. This one includes a fix for 2.2
    lockd when talking to HP/UX systems, NFS client fixes and cleanups for
    64bit ISDN support.
    
    What, exactly, is a local network address? Wietse Venema, the author
    of the [21]Postfix mailer, has a bit of a problem on his hands.
    Postfix has to be able to handle mail addressed to recipients like
    user@[1.2.3.4]; that involves figuring out whether 1.2.3.4 is a local
    address or not. This determination, as it turns out, is not as easy as
    one might think.
    
    The immediate problem is with IP aliasing. Linux has, for a long time,
    allowed more than one IP address to be assigned to a physical network
    interface. In more recent kernels, however, it is possible to set up
    aliases that do not have a separate name (i.e. eth0:0); if you ask the
    kernel for a list of local interface addresses (using the SIOCGIFCONF
    ioctl call), these "anonymous" aliases will be returned with an
    incorrect netmask. This is a relatively simple problem to fix, and
    Matthias Andree has put out [22]a patch to deal with it.
    
    It turns out, though, that SIOCGIFCONF does not return a complete list
    of local addresses. For example, 127.0.0.2 is a local address on
    almost all systems, as is the whole loopback subnet. The use of the
    advanced policy routing and proxying features in the 2.4 kernel
    complicates the situation further. The end result is that there is
    currently, no way to ask the kernel for the full list of local IP
    addresses. There are ways of finding out whether a specific address is
    local (the netlink interface), but there is no way of getting a list.
    
    And, even if there were, life would not get easier for mailer authors.
    It is not unheard of to configure a system with different mailers
    operating on different IP addresses. So an address which is "local"
    for the purposes of the kernel should be treated as remote by the
    mailer. To complicate things even further, a properly configured
    mailer [23]should look at the source of a message before deciding
    whether the IP number it is addressed to is local.
    
    In other words, with modern networking stacks, there is no way for the
    kernel to provide a mailer with a list of "local" IP addresses. The
    best solution would appear to be to stick with the old SIOCGIFCONF
    interface, and to have the mailer support a configuration file for
    systems with more complicated setups. Or, more likely, do nothing;
    continue to use the old interface, and get local delivery wrong in
    some rare situations.
    
    Yet another min/max implementation. One would think that the min/max
    discussion would fade away, and it mostly has. Morten Welinder,
    however, managed to come up with [24]yet another implementation which
    uses the old, two-argument interface, avoids side effect problems, and
    catches comparisons between signed and unsigned values (which was part
    of the motivation for the original change). It works by using a
    pointer comparison, which brings about a more specific type comparison
    at compile time.
    
    Linus proclaimed "[25]we have a winner," and stated his intention to
    include the patch in 2.4.10-pre5 - though a real solution wasn't
    posted until -pre8.
    
    Will write USB drivers for food. USB subsystem maintainer Johannes
    Erdfelt, once of VA Linux Systems, has [26]announced that he will be
    taking a short break from his duties while he looks for a new job. It
    seems that, as VA cuts back, it is no longer able to support as many
    kernel hackers. One hopes that Johannes will find a new position which
    allows him to continue working with the kernel. Meanwhile, Greg
    Kroah-Hartman is running the USB show.
    
    Other patches and updates released this week include:
    
      * David Miller has posted [27]an updated 64-bit PCI patch with a
        number of fixes.
      * Alex Bligh has posted [28]a proposal for dealing with
        fragmentation in the kernel's memory allocation code. It boils
        down to the creation of many new memory zones dedicated to certain
        types of tasks.
      * [29]A new preemptible kernel patch is available from Robert Love.
        It fixes a few problems, and adds a new CONFIG_PREEMPT
        configuration option. Note that this patch is still not
        well-tested on SMP systems.
      * Andrew Morton has posted [30]a new ext3 filesystem patch which
        incorporates some important fixes from Stephen Tweedie.
      * A new version of Richard Gooch's [31]patch for the handling of
        large numbers of SCSI devices has been posted.
        
    Section Editor: [32]Jonathan Corbet
    September 13, 2001
    
    For other kernel news, see:
      * [33]Kernel traffic
      * [34]Kernel Newsflash
      * [35]Kernel Trap
    
    Other resources:
      * [36]Kernel Source Reference
      * [37]L-K mailing list FAQ
      * [38]Linux-MM
      * [39]Linux Scalability Effort
      * [40]Kernel Newbies
      * [41]Linux Device Drivers
    
    
    
                                                   [42]Next: Distributions
    
    [43]Eklektix, Inc. Linux powered! Copyright Л 2001 [44]Eklektix, Inc.,
    all rights reserved
    Linux (R) is a registered trademark of Linus Torvalds
 
 References
 
    1. http://lwn.net/
    2. http://ads.tucows.com/click.ng/pageid=001-012-132-000-000-003-000-000-012
    3. http://lwn.net/2001/0913/
    4. http://lwn.net/2001/0913/security.php3
    5. http://lwn.net/2001/0913/dists.php3
    6. http://lwn.net/2001/0913/desktop.php3
    7. http://lwn.net/2001/0913/devel.php3
    8. http://lwn.net/2001/0913/commerce.php3
    9. http://lwn.net/2001/0913/press.php3
   10. http://lwn.net/2001/0913/announce.php3
   11. http://lwn.net/2001/0913/history.php3
   12. http://lwn.net/2001/0913/letters.php3
   13. http://lwn.net/2001/0913/bigpage.php3
   14. http://lwn.net/2001/0906/kernel.php3
   15. http://lwn.net/2001/0913/a/2.4.10-pre8.php3
   16. http://lwn.net/2001/0913/a/2.4.10-pre7.php3
   17. http://lwn.net/2001/0913/a/2.5-hint.php3
   18. http://lwn.net/2001/0913/a/2.4.9-ac10.php3
   19. http://lwn.net/2001/0913/a/ac-vm.php3
   20. http://lwn.net/2001/0913/a/ac-2.2.20-pre10.php3
   21. http://www.postfix.org/
   22. http://lwn.net/2001/0913/a/alias-patch.php3
   23. http://lwn.net/2001/0913/a/local-ip.php3
   24. http://lwn.net/2001/0913/a/yet-another-min.php3
   25. http://lwn.net/2001/0913/a/lt-yet-another-min.php3
   26. http://lwn.net/2001/0913/a/usb-maintainer.php3
   27. http://lwn.net/2001/0913/a/pci64.php3
   28. http://lwn.net/2001/0913/a/fragmentation.php3
   29. http://lwn.net/2001/0913/a/preemptible.php3
   30. http://lwn.net/2001/0913/a/ext3.php3
   31. http://lwn.net/2001/0913/a/devfs-scsi.php3
   32. mailto:lwn@lwn.net
   33. http://kt.zork.net/
   34. http://www.atnf.csiro.au/~rgooch/linux/docs/kernel-newsflash.html
   35. http://www.kerneltrap.com/
   36. http://lksr.org/
   37. http://www.tux.org/lkml/
   38. http://www.linux.eu.org/Linux-MM/
   39. http://lse.sourceforge.net/
   40. http://www.kernelnewbies.org/
   41. http://www.xml.com/ldd/chapter/book/index.html
   42. http://lwn.net/2001/0913/dists.php3
   43. http://www.eklektix.com/
   44. http://www.eklektix.com/
 
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