Re: [Xen-devel] [PATCH v6 4/5] fs, xfs: introduce MAP_DIRECT for creating block-map-atomic file ranges
[ adding Xen ] On Thu, Aug 24, 2017 at 9:11 AM, Christoph Hellwig wrote: > I still can't make any sense of this description. What is an external > agent? Userspace obviously can't ever see a change in the extent > map, so it can't be meant. 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 > It would help a lot if you could come up with a concrete user for this, > including example code. Will do. ___ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel
Re: [Xen-devel] [PATCH v6 4/5] fs, xfs: introduce MAP_DIRECT for creating block-map-atomic file ranges
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. ___ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel
Re: [Xen-devel] [PATCH v6 4/5] fs, xfs: introduce MAP_DIRECT for creating block-map-atomic file ranges
On Thu, Aug 24, 2017 at 9:39 AM, Christoph Hellwig 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. ___ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel