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    Subject[RFC]partitions through device-mapper
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    Hello, 

    now that the device mapper is merged into mainline, I would like to open a
    discussion on the possible in-kernel partition handling clean-up.

    In-kernel partition handling covers :
    o parsing of the on-disk partition tables
    o partition block devices creation / structs

    Along with initramfs will come the possibility to rip off the partition tables
    parsing from the kernel : a userspace parser like partx (part of util-linux
    toolset) can teach the kernel the partition layout.

    As driverfs provides elegantly block device add/remove events to hotplug, calls
    to partx can be wrapped into the block.agent

    The device-mapper merging could enable the ripping of all kernel partition
    understanding by creating linear device-maps over partitions.

    As a proof of concept, I've mutated partx to create those mappings. This tool
    is available for testing and commenting at :
    http://dsit.free.fr/dmpartx.tar.bz2

    This tool cannot damage your data : BLKPG_DEL_PARTITION and
    BLKPG_ADD_PARTITION ioctls are removed from the source.

    I would like to receive feedback over the following points :

    * Is this proposal completely out of the point ? Have I overlooked some
    important implementation details ?

    * driverfs send block device-removal-event at the end of the job, but device
    removal cannot happen as there are device-mappings over it. This ordering
    forbids hotplug to trigger the partition-mappings flush before block-device
    removal. Can this ordering be changed, or is there another solution ?

    * 2.5.44-ac4 did not notify block-device-add upon scsi disk insertion with
    scsi-add-single-device, which I think is known by scsi subsystem maintainers.
    -> The block.agent provided with dmpartx is not tested.

    * Should dmpartx create the 0-lengh partitions ? It does not at the moment.
    Extended partitions are handled the same way as partx : resize to 63 blocks


    regards,
    cvaroqui
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