On 08/24/2017 01:03 AM, Omar Sandoval wrote:
> From: Omar Sandoval <osandov@xxxxxx>
>
> Hi, everyone,
>
> Here's another attempt at supporting different logical block sizes for
> loop devices. First, some terminology:
>
> * Logical block size: the lowest possible block size that the storage
> device can address.
> * Physical block size: the lowest possible sector size that the
> hardware can operate on without reverting to read-modify-write
> operations. Always greater than or equal to the logical block size.
>
> These are characteristics of the device itself tracked in the
> request_queue. For loop devices, both are currently always 512 bytes.
>
> struct block_device also has another block size, basically a "soft"
> block size which is the preferred I/O size and can be changed from
> userspace. For loop devices, this is PAGE_SIZE if the backing file is a
> regular file or otherwise the soft block size of the backing block
> device.
>
> Patch 1 simplifies how the soft block size is set. I'm tempted to not
> set it at all and use the default of PAGE_SIZE, but maybe someone is
> depending on inheriting the soft block size from the backing block
> device...
>
> Patch 2 sets the physical block size of loop devices to a more
> meaningful value for loop, PAGE_SIZE.
>
> Patch 3 allows us to change the logical block size. It adds a new ioctl
> instead of the previous approach (which extends LOOP_{GET,SET}_STATUS).
> Hannes, I assume you had a specific reason for doing it the way you did,
> care to explain?
>
> Patch 4 is a cleanup.
>
> This is based on my patch reverting the original block size support,
> targeting 4.14. Thanks!
Applied for 4.14, thanks Omar.
--
Jens Axboe
