Hi, Dan, Referring to https://patchwork.kernel.org/project/linux-nvdimm/list/?page=6 [RFC,2/2] mm, fs: daxfile, an interface for byte-addressable updates to pmem I'm unable to find the patch in Linux upstream kernel, and am wondering if there has been a change of plan for providing support to byte granularity read() and write() to character device /dev/dax. I've also just started following the email threads, so I might have missed some critical discussions. Would you mind to elaborate what's happening to the proposed feature?

On Thu, Oct 19, 2017 at 2:41 PM, Jeff Moyer <jmoyer(a)redhat.com&gt; wrote: > jane.chu(a)oracle.com writes: > >> Hi, Dan, >> >> Referring to >> >> https://patchwork.kernel.org/project/linux-nvdimm/list/?page=6 >> >> [RFC,2/2] mm, fs: daxfile, an interface for byte-addressable updates >> to pmem >> >> I'm unable to find the patch in Linux upstream kernel, and am wondering if >> there has been a change of plan for providing support to byte granularity >> read() and write() to character device /dev/dax. >> >> I've also just started following the email threads, so I might have >> missed some critical discussions. Would you mind to elaborate what's >> happening to the proposed feature? > Device dax only supports mmap for data path access. There are no plans > to support read(2) or write(2). Yes, and the patch set referenced about was not about read(2)/write(2) it was about support for mmap writes without requiring them to be backstopped by calls to msync(). That proposal morphed into the MAP_SYNC and MAP_DIRECT proposals. MAP_SYNC is targeting 4.15. MAP_DIRECT is being reworked into an RDMA-memory-registration-specific interface.