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    SubjectRe: Bugs in mkfs.xfs, device mapper, xfs, and /dev/ram
    On Sat, Dec 04, 2010 at 04:11:40AM +1100, Nick Piggin wrote:
    > > Alternatively, what about switching brd away from overloading BLKFLSBUF
    > > to a real implementation of (overloaded) BLKDISCARD support in brd.c?
    > > One that doesn't blindly nuke the entire device but that properly
    > > processes the discard request.
    >
    > Yeah the situation really sucks (mkfs.jfs doesn't work on ramdisk
    > for the same reason).
    >
    > I want to unfortunately keep ioctl for compatibility, but adding new
    > saner ones would be welcome. Also, having a non-default config or
    > load time parameter for brd, to skip the special case, if that would
    > help testing on older userspace.

    How many programs actually depend on BLKFLSBUF dropping the pages used
    in /dev/ram? The fact that it did this at all was a historical
    accident of how the original /dev/ram was implemented (in the buffer
    cache directly), and not anything that was intended. I think that's
    something that we should be able to fix, since the number of programs
    that knowly operate on the ramdisk is quite small. Just a few system
    programs used by distributions in their early boot scripts....

    So I would argue for dropping the "special" behavior of BLKFLSBUF for
    /dev/ram.

    - Ted


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