Newsgroup: mailing.netbsd.tech.kern

Greetings,

I am trying to understand how block device read/write calls
communicate with the respective device driver strategy routines.
After a day of digging in both directions and in Bach and
Leffler I fail to find the common link; perhaps a kind
soul will enlighten me.

Tracing the call sequence from top to bottom for an ext2fs file
I end-up with a call to ufs_strategy with vp pointing to the
original vnode which will result in a series of further recursive 
calls to ufs_strategy.  

The sequence (in NetBSD 1.5) as I understand it is:

sys_generic.c:sys_write(...)

vfs_vnops:vn_write(...)

vnode_if.c:VOP_WRITE(vp, uio, ioflag, cred) {
	a.a_vp = vp;
	return (VCALL(vp, VOFFSET(vop_write), &a));

ext2fs_readwrite.c:ext2fs_write(v) {
	*ap = v;
	vp = ap->a_vp;
	ip = VTOI(vp)
	bp can be allocated by ext2fs_balloc(ip, ...)
		vp = ITOV(ip)
		which calls getblk(vp, ...)
			which using bgetvp(vp, bp) sets 
				bp->b_vp = vp;

vfs_bio.c:bwrite(bp) {
	VOP_STRATEGY(bp);

vnode_if.h:VOP_STRATEGY(bp) {
	a.a_bp = bp;
	return (VCALL(bp->b_vp, VOFFSET(vop_strategy), &a));

#define VCALL(VP,OFF,AP) VOCALL((VP)->v_op,(OFF),(AP))
#define VOCALL(OPSV,OFF,AP) (( *((OPSV)[(OFF)])) (AP))

ext2fs_vnops.c: { &vop_strategy_desc, ufs_strategy },

ufs_vnops.c:ufs_strategy(v)
	*ap = v;
	register struct buf *bp = ap->a_bp;
	register struct vnode *vp = bp->b_vp;
	VOCALL (vp->v_op, VOFFSET(vop_strategy), ap);

I then tried to go in the opposite direction.  The e.g. SCSI
strategy routine is stored as a pointer in a dk_driver structure
field. I grepped through the kernel source looking for it but 
could not find the point where this pointer is called or assigned
to another variable.

I am completely puzzled and will appreciate any help or just a
pointer to where I should look.

Thanks,

Diomidis -     http://www.spinellis.gr

Unless otherwise expressly stated, all original material on this page created by Diomidis Spinellis is licensed under a Creative Commons Attribution-Share Alike 3.0 Greece License.