Messages in this thread | | | Date | Wed, 01 Nov 2006 13:58:17 +0100 | From | Guillermo Marcus Martinez <> | Subject | Re: mmaping a kernel buffer to user space |
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Rolf Offermanns schrieb: > Guillermo Marcus <marcus <at> ti.uni-mannheim.de> writes: >> Note: I am using kernel 2.6.9 for these tests, as it is required by my >> current setup. Maybe this issue has already been addressed in newer >> kernel. If that is the case, please let me know. > > Have a look at this article: > > "The evolution of driver page remapping" > http://lwn.net/Articles/162860/ > > It should make things clearer. > > The "API changes in the 2.6 kernel series" page is also a very good read: > http://lwn.net/Articles/2.6-kernel-api/ > > HTH, > Rolf
Thanks for the links!
Yes, it looks like a step in the right direction. However, the article says about vm_insert_page(): "...What it does require is that the page be an order-zero allocation obtained for this purpose...", therefore making it also unusable for this case (mmaping a pci_alloc_consistent).
I think the limitation (being order zero), is related to the page counting, as I understand that for bigger order allocations, only the first-page counter is incremented (not every page). If that is a problem, I guess I would also see a problem with my workaround, and I see none (yet). So I may try in a newer kernel and see if I can use it to walk the pages on the mmap without using the nopage().
My suggestion would be to add two functions: pci_map_consistent() and dma_map_coherent() to address this issue, and their corresponding unmap's. That will make sure all that is needed is done, is a clean and consistent with the pci_ and dma_ APIs, and fills a mmap requirement not covered by the other functions.
Best wishes, Guillermo
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