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Date: | 2002-06-08 (13:36) |
From: | Xavier Leroy <xavier.leroy@i...> |
Subject: | Re: [Caml-list] camlimages and kernel memory |
> For example, Linux (but other OS, too) allow userland processes to access the > kernel memory by opening and mmapping the file /dev/kmem. This effects that > kernel memory is mapped into the userland address space. However, mmap is > usually restricted to 4k blocks, i.e. you can mmap only a whole number of > 4k blocks. > > O'Caml can handle pointers to blocks that are outside of the region that is > managed by its own routines. The blocks must have the right format, of course, > i.e. strings must have the right O'Caml header. I suppose this header is not > in the ringbuffer. > > If the ringbuffer happens to begin at a 4k boundary, you have won, because you > can manage that there is such a header without modifying kernel memory, i.e. > if the mmaped buffer begins at address A, just allocate anonymous memory in the > 4k block before A and write the needed header into it. This is the hard way :-) A simpler way to memory map files or devices in a Caml program is to use the function "map_file" from the Bigarray library. However, it currently always map the file from offset 0, which is probably not appropriate for /dev/kmem... I'll have to look into this limitation. > The other problem is whether camlimages can handle data that is > organized as ring. I don't have any ideas. The type Image.t is a relatively complex data structure, so some work is definitely needed to go from a raw string or bigarray (corresponding to the memory-mapped file) to a value of type Image.t. I'll let the authors of CamlImages comment on that. - Xavier Leroy ------------------- To unsubscribe, mail caml-list-request@inria.fr Archives: http://caml.inria.fr Bug reports: http://caml.inria.fr/bin/caml-bugs FAQ: http://caml.inria.fr/FAQ/ Beginner's list: http://groups.yahoo.com/group/ocaml_beginners