disk IO directly from PCI memory to block device sectors

[marty <martyleisner@yahoo.com>]

We  have a large ram area on a PCI board (think of a custom framebuffer
type application).  We're using 2.6.20.

We have the PCI ram mapped into kernel space, and knew the physical addresses.

We have a raw partition on the block device which we reserve for this.

We want to be able to stick the contents of selected portion of PCI ram onto a block device (disk).  Past incarnations modified the disk driver, and developed a special API so the custom driver  constructed scatter/gather lists and fed it to the driver (bypassing the elevator algorithm, to execute
as the "next request".

What I'm looking is for a more generic/driver independent way of sticking
contents of PCI ram onto a disk.

Is offset + length of each bio_vec < pagesize?

What's the best way to do this (much of my data is already in physically
contiguous memory [and mapped into virtual memory)). 

Any good examples to look at?

marty