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Old 02-16-2015, 04:56 AM   #1
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Registered: Feb 2015
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Block device drivers

I am new to drivers development under linux kernel. After starting with the simple examples from the book Linux Device Drivers v3, I realised that the block driver API has been totally changed since the kernel 2.6.31 or maybe later versions, and I couldn't find any documentation about the new API and how to use it. There are just some few comments in the source code.

After struggling for one month I almost had something working but few parts are missing or I misunderstood something.

Here is the situation :

After fetching the request with blk_fetch_request(q), I use the macro __rq_for_each_bio for handling the full request
To transfer the segments one by one I use the macro bio_for_each_segment(bvec, bio, i) that loops over all the segments in a bio

My question is :

I need to do some DMA from/to my device (the dma engine is within the device), that's why I need some address that I could use it to DMA from/to
Which buffer should I use ? for the moment I use the buffer returned by char *buffer=bio_data(bio), Does "buffer" corresponds to the physical buffer that I can use for DMA
How to end the request in this case ? using __blk_end_request_cur(req, 0) ? or using __blk_end_request(req, 0, bytes) ?

If you don't have an answer to any of these questions, where can I find a useful documentation for the new API of the block device drivers.
Old 02-18-2015, 09:22 AM   #2
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Registered: Feb 2015
Posts: 2

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I found it, I should have mapped the address returned from the bio structure with dma_map_single


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