About the request queue of block device

[Michael Zhu]

Hello, everyone, I have a question about the request
queue of block device.

I intercept the request function of floppy disk device
by changing the pointer, 
 "blk_dev[2].request_queue.request_fn", in my kernel
module. The following is the source code.

original_request_fn_proc =
blk_dev[2].request_queue.request_fn;
blk_dev[2].request_queue.request_fn =
my_request_fn_proc;

In my own my_request_fn_proc() I use the "req =
blkdev_entry_next_request(&rq->queue_head)" function
to get the pointer of the request structure. When
req->cmd is WRITE I encrypt all the b_data buffer of
the buffer header. Then I call the
original_request_fn_proc(). And it works. The data on
the floppy disk is some kind of cipher data. The
trouble is when the req->cmd is READ. I don't know
whether the b_data buffer contains the data read from
the floppy disk after I call the
original_request_fn_proc() function. When read a block
from the block device, where is the data is placed?

In my module I use the blkdev_next_request() function
to get the next request. When I want to do the same
thing to this next request, the Linux kernel
deadlocked. I must reboot the OS. What is wrong?

Any idea will be appreciated. Thanks in advance.

Michael

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