Messages in this thread |  | | Date | Tue, 10 Sep 2002 19:01:45 +0200 | From | Manfred Spraul <> | Subject | Re: Calculating kernel logical address .. |
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Andrew Morton wrote: > Manfred Spraul wrote: > >>Andrew Morton wrote: >> >>>Nobody seems to have come forth to implement a thought-out scatter/gather, >>>map-user-pages library infrastructure so I'd be a bit reluctant to >>>break stuff without offering a replacement. >>> >> >>We'd need one. >> >>get_user_pages() is broken if a kernel module access the virtual address >>of the page and the cpu caches are not coherent: > > > OK. Most users seem to just want to put the pages under DMA though. > > >>Most of the flush functions need the vma pointer, but it's impossible to >>guarantee that it still exists when the get_user_pages() user calls >>page_cache_release(). > > > Well presumably, if the driver is altering user memory by hand, > it is synchronous and they can hang onto mmap_sem while doing it? >
That's how it's done right now, and it works, but IMHO it's ugly. You switch from RAID-1 to RAID-5, and suddenly you might get unexplainable data corruptions with O_DIRECT.
-- Manfred
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