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    SubjectRe: plugging in 2.4. Does it work?
    Date
    "A month of sundays ago Jens Axboe wrote:"
    > On Wed, Feb 21 2001, Peter T. Breuer wrote:
    > > Hurrr ... are you saying that the buffers in the bh's in the request are
    > > not contiguous? My reading of the make_request code in 2.2 was that
    > > they were! Has that changed? There is now a reference to an elevator
    > > algorithm in the code, and I can't make out the effect by looking ...
    > > I have been copying the buffer in the request as though it were a single
    > > contigous whole. If that is not the case, then yes, bang would happen.
    >
    > Nothing has changed in this regard at all between 2.2 and 2.4. The
    > buffers are guaranteed to be sequentially sector-wise, but definitely
    > not contigious in memory!

    I recall that in 2.2 the make_request code tested that the
    buffers were contiguous in memory. From 2.2.18:

    /* Can we add it to the end of this request? */
    if (back) {
    if (req->bhtail->b_data + req->bhtail->b_size
    != bh->b_data) {
    if (req->nr_segments < max_segments)
    req->nr_segments++;
    else break;
    }

    It looks to me like it tested that the b_data char* pointers of the
    two requests being considered are exactly distant by the declared
    size of one.

    Is that no longer the case? If so, that's my answer.


    Peter
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