Test if VOP_BMAP actually works before using bmap/strategy.
When you create an image with
dd if=/dev/zero of=./netbsd.img bs=1m count=1 seek=1000
then the current check actually determines the "file system"
in the image supports VOP_BMAP and VOP_STRATEGY, but VOP_BMAP can't
translate any logical block numbers which results in EIO failures.
When you try to access the image in a Xen DomU you see all disk operations
failing. Therefore test if VOP_BMAP actually works and fall back to
VOP_READ/VOP_WRITE if it doesn't.
This makes a Xen DomU installation working. When you boot your fresh
installed Xen DomU with a valid disklabel and file system in the image,
VOP_BMAP actually works and is used.
This allows you to create an image with dd as above on the Dom0 and
run a DomU installation or to quickly create another virtual disk for
an existing DomU without having to create a disklabel and file system
by hand.
75946855ff