Dear Jonathan: 2011/11/1 Jonathan Corbet <corbet@xxxxxxx>: > On Tue, 1 Nov 2011 19:32:38 +0900 > loody <miloody@xxxxxxxxx> wrote: > >> My questions are below: > > As are some answers :) That will be great appreciated :) > >> 1. Are all struct page 32-bit aligned? > > Certainly, I would expect any structures found in the system memory map to > be so aligned, yes. If you've created an arbitrary one elsewhere I'm only > 99% sure it would be. > >> If so, where is this part of code for handleing struct page be 32-bits aligned? > > Note that the size of struct page is carefully considered, and that they > are packed as densely as possible, both externally and internally. No > lesser alignment would make sense. I found kernel stealing LSB of page_link to put additional information, such as sg_is_chain and sg_is_last. That means the address of all pages have to be at least 4byte alignment. But I didn't see any additional attribute added at the end of struct or any precaution to take care this. > >> 2. if the page of scatterlist is located at high mem, how does >> dma_map_sg mapping the virtual address? > > That depends on a vast array of things. What are the addressing > capabilities of the target device? Is there an IOMMU involved? No, my device has no iommu. and I found where kernel handle this part. > >> 3. in blk_rq_map_sg, it seems we only copy bvec->bv_page to sg->page_link >> why don't we add dma_address in bvec and send the bio directly to >> the lower level driver? > > That would be a bit of a mixing of the layers, if nothing else. > >> 4. if I plug a USB HD with 3 partitions, will there be 3 request_queues? > > No, there is one request queue for the underlying device. I study some block devices and it seems we use blk_init_queue for getting a request_queue, if we want block layer handle requests and coalesces adjacent requests. what happen and lower driver need to do if we don't use blk_init_queue to register a request_queue? > > That's an interesting mix of questions. If you have more in the future, > you'll likely get more (and more clueful) responses if they're accompanied > by the code you're working on. > > Thanks, > > jon -- Regards, _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
