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    SubjectRe: About the request queue of block device
    On Tue, Jan 08 2002, Michael Zhu wrote:
    > Hi, Jens, thank you very much for you kindly reply.
    > Your advice is very helpful to me. I've made some
    > revisions according to your advice. The attachment
    > contains some functions of mine. I don't know whether
    > I am right. I've done some test, but failed.
    >
    > In your mail you said that I can replace floppy
    > blk_dev
    > make_request_fn with my own that does the encryption
    > on write and stacks a new buffer head on top of the
    > other for READ, defining my own b_end_io function for
    > that to decrypt on READ end I/O. How can I stacks a
    > new buffer head on top of the other for READ? Is it
    > necessary? How to implement this? Please give me a
    > hand on this. Thank you very much.

    Yes it's necessary, you can't go fiddling with b_end_io b_private of a
    buffer you don't own. See loop.c

    > BTW, I've browsed the source code of __make_request()
    > function in the ll_rw_blk.c file. Do I need to call
    > the 'bh = create_bounce(rw, bh);' before I can access
    > the bh->b_data? You know the buffer data may point

    Inside make_request_fn, yes you need to bounce it yourself.

    > into the high memory. My failure is because of this?

    Probably not.

    --
    Jens Axboe

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