About block device request function.

[Michael Zhu]

Hi, I have a question of the block device request
function. I use the following sentences to change the
request function of a block device.

spin_lock_irq(&io_request_lock);

original_make_request_fn =
blk_dev[i].request_queue.make_request_fn;

blk_dev[i].request_queue.make_request_fn =
kti_make_request_fn;

spin_unlock_irq(&io_request_lock);

"i" is the major number of a block device.

You know blk_dev[] is the global block device array.
When I use those sentences to change the floppy block
device's request function, it works. The major number
of the floppy disk is 2. But when I use the same one
to change the hard disk's request function, it doesn't
work. I found that the
blk_dev[3].request_queue.make_request_fn is NULL. Does
that mean that the make_request_fn() of the hard disk
is NULL. I can't believe it. Can anyone give me an
answer?

Michael

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