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    SubjectRe: [dm-devel] Re: [RFC] device-mapper ioctl interface
    On Thursday 05 June 2003 19:50, Kevin Corry wrote:
    > On Thursday 05 June 2003 12:00, Daniel Phillips wrote:
    > > On Thursday 05 June 2003 18:47, Kevin Corry wrote:
    > > > 2) Removing suspended devices. The current code (2.5.70) does not allow
    > > > a suspended device to be removed/unlinked from the ioctl interface,
    > > > since removing it would leave you with no way to resume it (and hence
    > > > flush any pending I/Os). Alasdair mentioned a couple of new ideas. One
    > > > would be to reload the device with an error-map and force it to resume,
    > > > thus erroring any pending I/Os and allowing the device to be removed.
    > > > This seems a bit heavy-handed.
    > >
    > > Which is the heavy-handed part?
    > The part about automatically reloading the table with an error map and
    > forcing it to resume. It just seemed to me that user-space ought to be able
    > to gather enough information to determine that a device needed to be
    > resumed before it could be removed. Thus the kernel driver wouldn't be
    > forced to implement such a policy.

    I didn't see anything about doing that in-kernel.

    > Talking with Alasadair again, he mentioned a case I hadn't considered.
    > Devices would now be created without a mapping and initially suspended. If
    > some other error occurred, and you decided to just delete the device before
    > loading a mapping, it would fail. And having to resume a device with no
    > mapping just to be able to delete it definitely seems odd.
    > So, it's not like I'm dead-set against this idea. I was just curious what
    > the reasoning was behind this change.

    It's similar to the way a lot of things work in Linux: you have to let
    operations run to completion so they can let go of resources. One day we'll
    be able to shoot down transfers in mid-flight, but I doubt that's going to
    happen in this cycle.

    So in general, the idea is: let any outstanding operations complete, but feed
    them errors. What else can we do?

    I don't see this as heavyweight at all. Policy stays in user space, and a
    lightweight error path lives in the kernel.



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