[haiku-development] Re: BFS code questions

Janito Ferreira Filho <jvffprog@xxxxxxxxxxx> wrote:
> > This function is used for every read or write operation at least 
> > once - 
> > it's not an option to call anything else in there.
> > However, one should add a physical block size member to Volume, 
> > fill 
> > that during Mount(), and just use that through a getter method. 
> > Then 
> > indeed the DeviceOpener should retrieve the information (alongside 
> > the 
> > rest).
> Ok. I'll see if I can do that in the weekend =).

Okay.

> > It's initialized like this in line 1639:
> >     uint32 group = start >> fVolume->AllocationGroupShift();
> > 
> > The shift is the number of bits to shift a block offset in order to 
> > get 
> > the group index.
> Therefore it returns allocation group containing the block containing
> the "start" byte offset argument?

Exactly, just that "start" is in blocks, not bytes.

> > You are indeed missing something :-)
> > The incoming "start" argument is the first block to check. The 
> > CachedBlock is then set to the allocation group containing the that 
> > block (retrieved as above), and the block offset within that group 
> > ("groupBlock"). In each subsequent iteration, the groupBlock is 
> > incremented until the end of the current allocation group is reached 
> > which is when "group" is incremented as well, and "groupBlock" is 
> > reset 
> > to 0.
> Ok. I'm not sure I understood correctly. Does this mean every 
> allocation
> group contains it's own bitmap blocks?

Sort of - the whole block bitmap is divided into allocation groups.

> Sorry, for the false alarm... =)

No problem - better one time too often than living with a bug just 
because you didn't mention something; usually it hints to code that 
could receive some refactoring in order to make it clearer to 
understand, at the very least :-)

Bye,
   Axel.

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