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    SubjectRe: [RFC 02/22] configfs: Add struct configfs_item_operations->check_link() in configfs_unlink()
    On Tue, Sep 07, 2010 at 05:01:01PM -0400, Konrad Rzeszutek Wilk wrote:
    > > > I NAK'd this a while back. I'm willing to be convinced, but so
    > > > far it remains that way.
    > >
    > > Hi Joel,
    > >
    > > Thanks for bringing this point up again. So a brief refresh on why this
    > > is currently required in the fabric independent configfs handlers in
    > > drivers/target/target_core_fabric_configfs.c (patch #19).
    > Well, that is great that you mentioned your requirements. But I don't see a
    > quote of Joel's concerns? Is there an LKML link for it perhaps?

    It was a while back. Essentially, the concern is that configfs
    is defined to be userspace-driven. If the user asks you to remove
    something, the module should be handling safe teardown rather than
    rejecting the user's request.
    Now, the world isn't always clean-cut. Code outside of the
    filesystem representation can lay a claim on a configfs item to say "I'm
    busy with this." An example is ocfs2 pinning the configfs item
    describing its cluster heartbeat device. But this is ocfs2 - a
    separate thing - claiming it. There is a defined API to take and
    release these claims.
    This API doesn't cover symlinks, as symlinks are simply linkage
    between config items. It may be, as Nick suggested at the bottom of his
    reply, that we want the API extended to cover that case. But he hasn't
    yet convinced me that safe teardown is impossible or disasterous.
    That's what I'd like to see. It's not obvious on the face of all the
    file trees in the email.
    Nick, can you provide some form of description, not long
    pathnames, that explains a) what breaks when the symlink is removed b)
    why that can't be allowed if the user is dumb enough to request it?



    "The lawgiver, of all beings, most owes the law allegiance. He of all
    men should behave as though the law compelled him. But it is the
    universal weakness of mankind that what we are given to administer we
    presently imagine we own."
    - H.G. Wells

    Joel Becker
    Consulting Software Developer
    Phone: (650) 506-8127

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