On Thu, Aug 24, 2017 at 12:03:43AM -0700, Omar Sandoval wrote:
> From: Omar Sandoval <[email protected]>
>
> This is a different approach from the first attempt in f2c6df7dbf9a
> ("loop: support 4k physical blocksize"). Rather than extending
> LOOP_{GET,SET}_STATUS, add a separate ioctl just for setting the block
> size.
>
> Signed-off-by: Omar Sandoval <[email protected]>
> ---
> drivers/block/loop.c | 24 ++++++++++++++++++++++++
> include/uapi/linux/loop.h | 1 +
> 2 files changed, 25 insertions(+)
>
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index 1a5b4ecf54ec..6b1d932028e3 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -1047,6 +1047,7 @@ static int loop_clr_fd(struct loop_device *lo)
> memset(lo->lo_encrypt_key, 0, LO_KEY_SIZE);
> memset(lo->lo_crypt_name, 0, LO_NAME_SIZE);
> memset(lo->lo_file_name, 0, LO_NAME_SIZE);
> + blk_queue_logical_block_size(lo->lo_queue, 512);
> if (bdev) {
> bdput(bdev);
> invalidate_bdev(bdev);
> @@ -1330,6 +1331,24 @@ static int loop_set_dio(struct loop_device *lo,
> unsigned long arg)
> return error;
> }
>
> +static int loop_set_block_size(struct loop_device *lo, unsigned long arg)
> +{
> + if (lo->lo_state != Lo_bound)
> + return -ENXIO;
> +
> + if (arg < 512 || arg > PAGE_SIZE || !is_power_of_2(arg))
> + return -EINVAL;
I'm not sure if the PAGE_SIZE is the right limit for the use-case
where backing file is a block device ...but it's nothing important.
> + blk_mq_freeze_queue(lo->lo_queue);
> +
> + blk_queue_logical_block_size(lo->lo_queue, arg);
Just note that this function also updates physical_block_size if the
'arg' is greater than the current setting. That's good thing :-)
> + loop_update_dio(lo);
> +
> + blk_mq_unfreeze_queue(lo->lo_queue);
> +
> + return 0;
> +}
> +
> static int lo_ioctl(struct block_device *bdev, fmode_t mode,
> unsigned int cmd, unsigned long arg)
> {
> @@ -1378,6 +1397,11 @@ static int lo_ioctl(struct block_device *bdev, fmode_t
> mode,
> if ((mode & FMODE_WRITE) || capable(CAP_SYS_ADMIN))
> err = loop_set_dio(lo, arg);
> break;
> + case LOOP_SET_BLOCK_SIZE:
> + err = -EPERM;
> + if ((mode & FMODE_WRITE) || capable(CAP_SYS_ADMIN))
> + err = loop_set_block_size(lo, arg);
> + break;
I like it this ioctl idea. It makes loop based tests more comfortable
as we can change sector size on the fly without loop device reset.
I did not test it yet, but this implementation seems the best. Thanks.
Karel
--
Karel Zak <[email protected]>
http://karelzak.blogspot.com
