Re: route inode->block_device in 2.5?

[Andrew Morton]

Alexander Viro wrote:
> 
> ...
> There might be such thing as underlying block device of a <foofs> inode.

What he said.  Generally when the generic layers want to know
what the backing block_device is they defer this all the way down
to the point where they have called the filesystem's ->get_block
callback, and they pluck the block_dev pointer out of bh_result->b_bdev.

That's the only point at which it can be sanely resolved.

It may be different for different blocks of the file (striping;
swap_get_block() did this for the short period when it nearly
existed).