Re: [RFC] block integrity: Fix write after checksum calculation problem

[Chris Mason]

Excerpts from Joel Becker's message of 2011-02-23 15:24:47 -0500:
> On Tue, Feb 22, 2011 at 11:45:44AM -0500, Martin K. Petersen wrote:
> > Also, DIX is only the tip of the iceberg. Many other impending
> > technologies feature checksums and require pages to be stable during I/O
> > due to checksumming, encryption and so on.
> > 
> > The VM is already trying to do the right thing. We just need the
> > relevant filesystems to catch up.
> 
>     ocfs2 handles stable metadata for its checksums when feeding
> things to the journal.  If we're doing pagecache-based I/O, is the
> pagecache going to help here for data?

Data is much easier than metadata.  All you really need is to wait on
writeback in file_write, wait on writeback in page_mkwrite, and make
sure you don't free blocks back to the allocator that are actively under
IO.

I expect the hard part to be jbd and metadata in ext34.

-chris
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