On Thu, Nov 4, 2021 at 1:27 PM Jane Chu <jane.chu@xxxxxxxxxx> wrote: > > On 11/4/2021 12:00 PM, Dan Williams wrote: > > >> > >> If this understanding is in the right direction, then I'd like to > >> propose below changes to > >> dax_direct_access(), dax_copy_to/from_iter(), pmem_copy_to/from_iter() > >> and the dm layer copy_to/from_iter, dax_iomap_iter(). > >> > >> 1. dax_iomap_iter() rely on dax_direct_access() to decide whether there > >> is likely media error: if the API without DAX_F_RECOVERY returns > >> -EIO, then switch to recovery-read/write code. In recovery code, > >> supply DAX_F_RECOVERY to dax_direct_access() in order to obtain > >> 'kaddr', and then call dax_copy_to/from_iter() with DAX_F_RECOVERY. > > > > I like it. It allows for an atomic write+clear implementation on > > capable platforms and coordinates with potentially unmapped pages. The > > best of both worlds from the dax_clear_poison() proposal and my "take > > a fault and do a slow-path copy". > > > >> 2. the _copy_to/from_iter implementation would be largely the same > >> as in my recent patch, but some changes in Christoph's > >> 'dax-devirtualize' maybe kept, such as DAX_F_VIRTUAL, obviously > >> virtual devices don't have the ability to clear poison, so no need > >> to complicate them. And this also means that not every endpoint > >> dax device has to provide dax_op.copy_to/from_iter, they may use the > >> default. > > > > Did I miss this series or are you talking about this one? > > https://lore.kernel.org/all/20211018044054.1779424-1-hch@xxxxxx/ > > I was referring to > > http://git.infradead.org/users/hch/misc.git/shortlog/refs/heads/dax-devirtualize > that has not come out yet, I said early on that I'll rebase on it, > but looks like we still need pmem_copy_to/from_iter(), so. Yeah, since the block-layer divorce gets rid of the old poison clearing path, then we're back to pmem_copy_to_iter() (or something like it) needing to pick up the slack for poison clearing. I do agree it would be nice to clean up all the unnecessary boilerplate, but the error-list coordination requires a driver specific callback. At least the DAX_F_VIRTUAL flag can eliminate the virtiofs and fuse callbacks.
