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Old 11-15-2012, 03:12 AM   #1
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Question bio structure - control over creation

Hi all,

I'm creating a block driver, and have some problems with configuring the request.

The characteristics of my device are very similar to those of NAND flash, i.e., there is no benefits from sequential IOs (time for random IO is constant - no mechanics, no positioning).

I use "make_request" approach in driver.
The size of logical blocks (IO units) can vary (depending on the initial configuration of a device): 512, 1024, 2048, 4096,...

Question 1:
If the size of logical block is less than PAGE_SIZE (e.g., 512Kb, 1024Kb), could I somehow tell a system to create bio's only 1 logical block in size?
The minimal value for max_hw_sectors (set via blk_queue_max_hw_sectors) is 8 =>so it is not suited to restrict bio to be always, for example, 512 bytes.

Question 2:
Here, as opposite to question 1, the bio can consist of multiple logical blocks. If one logical block is represented via multiple segments (bi_vec) - it's ok. The problem is when one segment (bi_vec) refferes to data from multiple logical blocks. Is it possible somehow to control the segmentation of bio or to align the segemnts to logical blocks?

Thanks a lot for any help!


block device

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