On Mon, Aug 26, 2019 at 04:51:52AM -0700, Christoph Hellwig wrote: > On Wed, Aug 21, 2019 at 01:57:02PM -0400, Vivek Goyal wrote: > > From: Stefan Hajnoczi <stefanha@xxxxxxxxxx> > > > > Although struct dax_device itself is not tied to a block device, some > > DAX code assumes there is a block device. Make block devices optional > > by allowing bdev to be NULL in commonly used DAX APIs. > > > > When there is no block device: > > * Skip the partition offset calculation in bdev_dax_pgoff() > > * Skip the blkdev_issue_zeroout() optimization > > > > Note that more block device assumptions remain but I haven't reach those > > code paths yet. > > I think this should be split into two patches. Hi Christoph, Ok, will split in two patches. In fact, I think will completley drop the second change right now as I think we might not be hitting that path yet. > For bdev_dax_pgoff > I'd much rather have the partition offset if there is on in the daxdev > somehow so that we can get rid of the block device entirely. IIUC, there is one block_device per partition while there is only one dax_device for the whole disk. So we can't directly move bdev logical offset into dax_device. We probably could put this in "iomap" and leave it to filesystems to report offset into dax_dev in iomap that way dax generic code does not have to deal with it. But that probably will be a bigger change. Did I misunderstand your suggestion. > > Similarly for dax_range_is_aligned I'd rather have a pure dax way > to offload zeroing rather than this bdev hack. Following commig introduced the change to write zeros through block device path. commit 4b0228fa1d753f77fe0e6cf4c41398ec77dfbd2a Author: Vishal Verma <vishal.l.verma@xxxxxxxxx> Date: Thu Apr 21 15:13:46 2016 -0400 dax: for truncate/hole-punch, do zeroing through the driver if possible IIUC, they are doing it so that they can clear gendisk->badblocks list. So even if there is pure dax way to do it, there will have to some involvment of block layer to clear gendisk->badblocks list. I am not sure I fully understand your suggestion. But I am hoping its not a must for these changes to make a progress. For now, I will drop change to dax_range_is_aligned(). Thanks Vivek
