How to filter the Block I/O in 2.6 kernel?

[XiongJia Le]

How to filter the Block I/O in 2.6 kernel?

I have looked some in blktrace.
blktrace can trace the block device I/O info. But that can't
filter/change this I/O.

Is the Linux kernel have any way to filter/change a block i/o before
it write to hard disk?
I don't want to change kernel code and re-build. Is Kernel already
have any I/O filter interface?

Thanks,
Xiongjia Le
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