On Thu, Aug 24, 2017 at 9:39 AM, Christoph Hellwig <hch@xxxxxx> wrote: > On Thu, Aug 24, 2017 at 09:31:17AM -0700, Dan Williams wrote: >> External agent is a DMA device, or a hypervisor like Xen. In the DMA >> case perhaps we can use the fcntl lease mechanism, I'll investigate. >> In the Xen case it actually would need to use fiemap() to discover the >> physical addresses that back the file to setup their M2P tables. >> Here's the discussion where we discovered that physical address >> dependency: >> >> https://lists.xen.org/archives/html/xen-devel/2017-04/msg00419.html > > fiemap does not work to discover physical addresses. If they want > to do anything involving physical address they will need a kernel > driver. True, it's broken with respect to multi-device filesystems and these patches do nothing to fix that problem. Ok, I'm fine to let that use case depend on a kernel driver and just focus on fixing the DMA case.
