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SubjectRe: [patch] block device stacking support, raid-2.3.47-B6

On Wed, 23 Feb 2000, Andrea Arcangeli wrote:

> >- renaming ->make_request_fn() to ->logical_volume_fn is both misleading
> > and unnecessery.
>
> Note that with my proposal it was make_request_fn to be misleading because
> all the code run within the callback had anything to do with the
> make_request code.

ok, your variant was more like a ->map_buffer_fn() thing - like the old
md_map() stuff. ->make_request_fn() is closer to 'make request' in the
context of RAID1 and RAID5. (even if this is not visible now).

> > - device resolves recursion internally and returns 0 (future RAID0),
> > returns 1 if recursion cannot be resolved internally.
>
> I don't think it worth to handle such case if it costs something for the
> other cases. I'll check and test the code on the LVM side soon.

the cost is only in the device (not in the generic block IO code), it's a
'if (MAJOR(bh->b_rdev) == MD_MAJOR) goto repeat;' type of thing (analogous
in the LVM code), nothing more. We will see how common it gets - it's just
a nice side-effect that th possibility is there.
Ingo


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