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    SubjectRe: bug in md write barrier support?
    On Saturday September 4, wrote:
    > On Sat, Sep 04 2004, Neil Brown wrote:
    > > On Friday September 3, wrote:
    > > > md_flush_mddev just passes on the sector relative to the raid device,
    > > > shouldn't it be translated somewhere?
    > >
    > > Yes. md_flush_mddev should simply be removed.
    > > The functionality should be, and largely is, in the individual
    > > personalities.
    > Yes, sorry I was a little lazy there even though I followed the plugging
    > conversion :(
    > > Is there documentation somewhere on exactly what an issue_flush_fn
    > > should do (is it allowed to sleep? what must happen before it is
    > > allowed to return, what is the "error_sector" for, that sort of thing).
    > It is allowed to sleep, you should return when the flush is complete.
    > error_sector is the failed location, which really should be a dev,sector
    > tupple.

    Could I get a little more information about this function please.
    I've read through the code, and there isn't much in the way of
    examples to follow: only reiserfs uses it, only scsi-disk and ide-disk
    supports it (I think).

    It would seem that this is for write requests where b_end_io has already
    been called, indicating that the data is safe, but that maybe the data
    isn't really safe after-all, and blk_issue_flush needs to be called.

    I would have thought that after b_end_io is called, that data should
    be safe anyway. Not so?

    How do you tell a device: it is OK to just leave the data is cache,
    I'll call blk_issue_flush when I want it safe.
    Is this related to barriers are all??

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