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    SubjectRe: Kernel SCM saga..
    On Fri, Apr 08, 2005 at 12:03:49PM -0700, Linus Torvalds wrote:

    > And if you do actively malicious things in your own directory, you get
    > what you deserve. It's actually _hard_ to try to fool git into believing a
    > file hasn't changed: you need to not only replace it with the exact same
    > file length and ctime/mtime, you need to reuse the same inode/dev numbers
    > (again - I didn't worry about portability, and filesystems where those
    > aren't stable are a "don't do that then") and keep the mode the same. Oh,
    > and uid/gid, but that was much me being silly.

    It would be even easier to touch the tree with a known date before
    patching (eg:1/1/70). It would protect against any accidental date
    change if for any reason your system time went backwards while
    working on the tree.

    Another trick I use when I build the 2.4-hf patches is to build a
    list of filenames from the patches. It works only because I want
    to keep all original patches and no change should appear outside
    those patches. Using this + cp -al + diff -pruN makes the process
    very fast. It would not work if I had to rebuild those patches from
    hand-edited files of course.

    Last but not least, it only takes 0.26 seconds on my dual athlon
    1800 to find date/size changes between 2.6.11{,.7} and 4.7s if the
    tool includes the md5 sum in its checks :

    $ time flx check --ignore-owner --ignore-mode --ignore-ldate --ignore-dir \
    --ignore-dot --only-new --ignore-sum linux-2.6.11/. linux-2.6.11.7/. |wc -l
    47

    real 0m0.255s
    user 0m0.094s
    sys 0m0.162s

    $ time flx check --ignore-owner --ignore-mode --ignore-ldate --ignore-dir \
    --ignore-dot --only-new linux-2.6.11/. linux-2.6.11.7/. |wc -l
    47

    real 0m4.705s
    user 0m3.398s
    sys 0m1.310s

    (This was with 'flx', a tool a friend developped for file-system integrity
    checking which we also use to build our packages). Anyway, what I wanted
    to show is that once the trees are cached, even somewhat heavy operations
    such as checksumming can be done occasionnaly (such as md5 for double
    checking) without you waiting too long. And I don't think that a database
    would provide all the comfort of a standard file-system (cp -al, rsync,
    choice of tools, etc...).

    Willy

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