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    SubjectRe: Revoking filesystems [was Re: Sysfs attributes racing with unregistration]
    On Thu, Jan 05, 2012 at 01:27:52PM -0500, Ted Ts'o wrote:
    > Ideally, we should do both. The block device should call a
    > notification function (probably run out of a workqueue context, to
    > avoid locking issues) which tells the file system, "the block device
    > is _gone_ and isn't coming back". Any attempts to read or write to
    > the block device should return errors, since there maybe writeback
    > happening in the background while the file system is shutting down
    > file system mount. Once the file system is done, it can all a
    > function which tells the block device layer that it's OK to release
    > the block device and its related structures.

    FYI: we have all the functionality for that available in XFS and would
    just need to wire it up. It's also triggered if we get a write I/O
    error for metadata (typically the log), so with a minim delay we
    actually provide that behaviour already.

    > In order for the file system to shut down the file system cleanly, it
    > will need to access VFS-level revoke functionality that replaces file
    > descriptors with ones that returns an error on reads and writes, and
    > which does the right thing with mmap's[1], etc.

    And that part is close to impossible to get right.

     \ /
      Last update: 2012-01-05 19:41    [W:0.019 / U:9.520 seconds]
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