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    SubjectRe: IDE HPA
    Peter Jones wrote:
    > So where would you envision this code to check the partition table, the
    > HPA/host default disk size, and guess how things should be set up?
    >>From a userland perspective, it's very difficult to let users know
    > they'll be screwing themselves by partitioning the entire disk, so we
    > really should be leaving HPA enabled if the protected area is indeed not
    > for consumption.
    > Also, the heuristic is harder than this -- if we reexamine the fakeraid
    > case, then it's clear we have to look for raid metadata, figure out if
    > the raid includes stuff inside the HPA or not, and then if it doesn't we
    > don't care -- but that's assuming there _is_ raid metadata.
    > Long term, many people hope, possibly unrealistically, that we'll be
    > able to write out raid metadata for people creating raids on cards which
    > support fakeraid, and have the BIOS grok it appropriately. So in that
    > case, we may well have a blank (or garbage) disk, and we can't check the
    > partition table or any raid metadata. Correct me if I'm wrong, but I
    > don't see a simple heuristic for this case.
    > (as a side note, I know one user who, at OLS, noticed we fail to
    > re-initialize HPA after unsuspend, so on at least t40 the disk gets
    > smaller when you suspend. This may or may not be fixed, I haven't
    > checked. But it's one more sort of pain we get into by disabling it,
    > whether justified or not.)

    It seems to me that one should write an ATA-specific Device Mapper
    driver, which layers on top of an ATA disk. The driver obtains the
    starting location of HPA, then exports two block devices: one for the
    primary data area, and one for the HPA.

    For situations where we want the start Linux philosophy -- Linux exports
    100% of the hardware capability -- no DM layer needs to be used. For
    situations where its better to treat the HPA as a separate and distinct
    area, the DM driver would come in handy.

    This follows the same philosophy as fakeraid (BIOS RAID): we simply
    export the entire disk, and Device Mapper (google for 'dmraid') handles
    the vendor-proprietary RAID metadata.


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