> >> Background:
> >> Ideally struct buf should have had a real OO like operations vector
> >> like vnodes have it, and struct bioops is the first step towards that.
> >> 
> >struct buf will eventually become merely an iocmd structure, so why do
> >we want to complicate things here?
> No, struct buf will remain the cache-handle. the iocmd is called
> struct bio.
Even if struct buf stays around, its cache-handle role will be diminished,
probably just a translation layer to vm object based caching.

> >We already have an OO method for bwrite: VOP_BWRITE(), the problem
> >is most of the code are still calling bwrite() directly. Will it
> >solve your problem if we change every bwrite() into a VOP_BWRITE()?
> Well, I'm not sure it is correct to go the detour around Vnodes,
> if we do, we need to add VOP_BAWRITE, VOP_BDWRITE and all those
> other operations as well.
Don't you need bp->b_ops->bawrite(), bp->b_ops->bdwrite() as well?
I feel it's better to go through the vnode, because for all the bufs
belong to the same vnode, these b_ops are most likely to be the same.
And for a stackable filesystem, you may easily implement a passthru
call with vnode, how would you deal with it using struct buf?

> But what vnode would you use for a buffer associated with a freeblock
> bitmap ?
Each buffer belongs to a vnode, a buffer associated with a freeblock bitmap
belongs to the device vnode, and that's the vnode we could use.

> --
> Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
> [EMAIL PROTECTED]         | TCP/IP since RFC 956
> FreeBSD coreteam member | BSD since 4.3-tahoe    
> Never attribute to malice what can adequately be explained by incompetence.


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