On Wed, Jul 21, 2021 at 08:48:57AM -0400, Vivek Goyal wrote: [..] > > > So is "dax=inode" enough for your needs? What's your requirement, > > > can you give little bit of more details. > > > > In our use case, the backend fs is something like SquashFS on host. The > > content of the file on host is downloaded *as needed*. When the file is > > not completely ready (completely downloaded), the guest will follow the > > normal IO routine, i.e., by FUSE_READ/FUSE_WRITE request. While the file > > is completely ready, per-file DAX is enabled for this file. IOW the FUSE > > server need to dynamically decide if per-file DAX shall be enabled, > > depending on if the file is completely downloaded. > > So you don't want to enable DAX yet because guest might fault on > a section of file which has not been downloaded yet? > > I am wondering if somehow user fault handling can help with this. > If we could handle faults for this file in user space, then you > should be able to download that particular page[s] and resolve > the fault? Stefan mentioned that can't we block when fuse mmap request comes in and download corresponding section of file. Or do whatever you are doing in FUSE_READ. IOW, even if you enable dax in your use case on all files, FUSE_SETUPMAPPING request will give you control to make sure file section being mmaped has been downloaded. Vivek
