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    SubjectRe: Hibernating To Swap Considered Harmful
    On Tue, 17 Jul 2007, Joseph Fannin wrote:

    > On Mon, Jul 16, 2007 at 11:42:08PM -0700, wrote:
    >> On Tue, 17 Jul 2007, Joseph Fannin wrote:
    >>> root is free to "dd if=/dev/random of=/dev/mem". Root owned
    >>> daemons which do bad things are bugs.
    >> in this case it would be more like
    >> dd if=/block0 of=/dev/sda1 count=1 bs=4096 skip=5000
    >> dd if=/block1 of=/dev/sda1 count=1 bs=4096 skip=5050
    >> dd if=/block2 of=/dev/sda1 count=1 bs=4096 skip=5400
    >> etc
    >> to write the blocks to the raw parition in the right place
    > What I meant by that was that root is allowed to shoot himself in the
    > foot. Nothing stops root from opening a swap/hibernate file, which
    > would put it in cache, and cause it to be inconsistant if a
    > hibernation image was written to it behind the kernel's back.
    > That would be a very stupid thing to do, however. There's no reason
    > to open that file, unless you know *exactly* what you are doing, in
    > which case the onus is on you to get it right.
    > But you have a point. The swap file could be very fragmented. It
    > might often be so, even.
    > Still, is this better than exporting the kernel's swap internals
    > (which has never been a public interface before)?
    > Does it make the interface that writing hibernation images to swap
    > imposes any better?
    > Even if hibernation files are no less complicated to support than
    > hibernating to swap files (which isn't a forgone conclusion) , there
    > are plenty of reasons writing hibernation images to swap doesn't make
    > sense.
    >>> Again, supporting swap files (*which is not optional*) requires the
    >>> very same support.
    >> in the kexec model why would the second kernel care about swap files at
    >> all? (unles it chooses to write to them, in which case it is exactly the
    >> same support, but unless it writes to them it doesn't need to care)
    > My point is that no extra work is required to write hibernation images
    > to dedicated files than to write hibernation images to swap files.
    > If swap files are to be supported, then, there's no technical reason
    > not to support dedicated hibernation files. Dedicated hibernation
    > files are better, and there's no reason not to implement them.

    I agree with your point, but the reverse is not true, the ability to write
    to a dedicated hibernation file does not produce the capacity to write to
    a swap file, and I do question the 'requirement' to write the hibernation
    image to the swap file.

    David Lang

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      Last update: 2007-07-17 09:43    [W:0.049 / U:0.056 seconds]
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