> + /*
> + * loop block's logical block size is 512, now
> + * we support direct I/O only if the backing
> + * block devices' minimize I/O size is 512 and
> + * the offset is aligned with 512.
> + */
> + if (dio) {
> + if (inode->i_sb->s_bdev &&
> + bdev_io_min(inode->i_sb->s_bdev) == 512 &&
> + !(lo->lo_offset & 511))
Why the hardcoded value? I suspect this should be more like:
if (dio && inode->i_sb->s_bdev &&
(lo->lo_offset & (bdev_io_min(inode->i_sb->s_bdev) - 1)) != 0)
dio = false;
> + blk_mq_freeze_queue(lo->lo_queue);
> + lo->use_dio = use_dio;
> + if (use_dio)
> + lo->lo_flags |= LO_FLAGS_DIRECT_IO;
> + else
> + lo->lo_flags &= ~LO_FLAGS_DIRECT_IO;
> + blk_mq_unfreeze_queue(lo->lo_queue);
Locking?
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