[dm-devel] Re: [PATCH 12/17] bottom-layer barrier support

[Alasdair G Kergon]

On Mon, Apr 27, 2009 at 07:32:00PM -0400, Mikulas Patocka wrote:
> On entry to the function it holds zero if it is processing zero-length 
> barrier. 

OK - so that is a clear definition the writer of a target map function can
rely upon, good.

> The line "bio->bi_sector = dc->start_write + (bio->bi_sector - 
> ti->begin)" can set it to non-zero, so I set it to zero again. If you 
> want, you can somehow rearrange the code so that "bio->bi_sector = 
> dc->start_write + (bio->bi_sector - ti->begin)" is performed only if the 
> request has non-zero length.
 
Please do that.  In dm I try to enforce a rule that the values of variables
always correspond to their definitions - if a calculation needs intermediate
steps then different and meaningful intermediate variables are used
instead.  Here, bi_sector seems to be set to a meaningless intermediate
value which is a recipe for confusion.

Alasdair
-- 
agk at redhat.com