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    SubjectRe: Problem w/ CONFIG_DEBUG_BLOCK_EXT_DEVT
    Tejun Heo wrote:
    > Hello,
    > Alan D. Brunelle wrote:
    >> I have found two problems in LVM2/DM w/ a potential new "experimental
    >> feature" in 2.6.28: CONFIG_DEBUG_BLOCK_EXT_DEVT (this is from Jens
    >> Axboe's origin/for-2.6.28 git branch)
    > It's a debug option and I don't expect it to be enabled in any
    > production kernel.

    Then perhaps it should /not/ default to Y...

    >> "Conventionally, block device numbers are allocated from predetermined
    >> contiguous area. However, extended block area may introduce
    >> non-contiguous block device numbers. This option forces most block
    >> device numbers to be allocated from the extended space and spreads them
    >> to discover kernel or userland code paths which assume predetermined
    >> contiguous device number allocation."
    >> W/ LVM2 & DM there are (at least) two issues:
    >> (1) Device major numbers for some reason are /not/ being entered
    >> correctly into /proc/devices -- w/ CONFIG_DEBUG_BLOCK_EXT_DEVT=y I am
    >> seeing some devices w/ major "259" (a SATA controller) but no entry in
    >> /proc/devices. LVM2/DM will not find the entry in /proc/devices, and not
    >> allow any device w/ that major to be used with LVM commands.
    > Hmmm.. Adding a call to register_blkdev(), which will create the
    > corresponding entry in /proc/devices, isn't difficult at all but which
    > name would it use? It'll be mix of block devices (hd and sds
    > currently). If we introduce a new name there, say, ext-block, would
    > that work? BTW, is there any specific reason why LVM2/DM can't use
    > /sys/block/* ?
    >> (2) Device minor numbers can be quite large, and the 10-character limits
    >> in dm/lib/libdm-deptree.c are too small.
    > Would it be difficult to increase that?

    No, but knowing the upper bound would be helpful.

    > Thanks.

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