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

[Mikulas Patocka <mpatocka redhat com>]

On Tue, 28 Apr 2009, Alasdair G Kergon wrote:

> 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.

OK.

Mikulas

> Alasdair
> -- 
> agk redhat com
>