hi, > Here's the reason why I've written xmd_machdep.c: > > xmd(4) is a read-only RAM-based disk driver capable of XIP. The > main purpose is to test XIP functionality. xmd(4) can be implemented > on any platforms that supports VM in theory. xmd(4) may be also > useful for other cases where md(4) is used, but users want to save > memory. md(4) allocates memory for its storage, and copies pages > from or to page cache. > > xmd(4) allocates a static, read-only array and provides it as a > backing store. When it's used as XIP, it registers the array as > a physical device page segment. From VM's POV, the registered > region is seen like a ROM in a device connected over some buses. > > The procedure to register an array as a physical segment is somewhat > strange. The registered array resides in kernel's read-only data > section. Kernel already maps its static region (text, rodata, > data, bss, ...) at boot time. xmd(4) "re-defines" part of it as > a physical device segment, like a ROM connected via another bus. > > As far as the backing store array resides in main memory, you'll > end up with some way to convert kernel VA back to physical address. > There is no alternative to achieve the goal in MI way, or xmd.c is > sprinkled like mem.c.
why can't you use pmap_extract? YAMAMOTO Takashi > > Masao
