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    SubjectRe: introduce dm-snap-mv
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    On Fri, Oct 8, 2010 at 5:24 PM, Christoph Hellwig <hch@lst.de> wrote:
    > On Fri, Oct 08, 2010 at 05:14:27PM +0800, McPacino wrote:
    >> Hi Christoph,
    >>
    >> I have to take care the cache problem If using the bio directly.
    >> BHs can be released by kernel when necessary.
    >>
    >> Is there any existing code using bio to read/write metadata
    >> blocks? How do they handle the timing freeing bios? I really
    >> wish to learn something form it.
    >
    > If you actually need caching just use the pagecache, e.g.
    > read_mapping_page to read in your data.  That completely abstracts
    > away the underlying block size.

    Hi Christoph,

    My understanding is that, read_mapping_page_async() works in submit-wait
    way. But whatI want is some function works in submit-callback way, just like
    sumbit_bh(). Is there something like it in kernel?

    thanks.
    cong meng.

    >
    >
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