Messages in this thread | | | Date | Thu, 5 Jan 2012 13:38:32 -0500 | From | Christoph Hellwig <> | Subject | Re: Revoking filesystems [was Re: Sysfs attributes racing with unregistration] |
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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.
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