getting from bio to buf in dastrategy()

[Eno Thereska]

Hi all,

I am hacking into the FreeBSD 5.0 code.
I jumped from using 4.4 to 5.0 and a couple of things
have changed. Here is my question:

in /sys/cam/scsi/scsi_da.c the dastrategy()
function takes as an argument "struct bio* bp"
Now I need to get to the "struct *buf" that bp
belongs to. In /sys/sys/buf.h I see that
struct buf has as the first member "b_io" which is
of type struct bio. I also see the BIOTOBUF
#define which is supposed to take a bio and
return the buf it belongs to.

Now in dastrategy() if I use the BIOTOBUF function
and try to access members of the struct buf
I get junk, which means that the bio passed to the
is not directly related to a buf. Am I missing something
here? How do I know to which buf (if any) the bio belongs
to?

Also it seems to me that the new way of
splitting the old struct buf into a
struct bio and having a bunch of #defines inside
the struct buf is kind of hacky. What was the
rationale behind doing that (rather than
just leaving it the way it was in 4.4)?

Thanks
Eno