On Wed, Aug 19, 2020 at 11:25 AM Amir Goldstein <amir73il@xxxxxxxxx> wrote: > > What I have in mind is things like not coupling the setup of the > > passthrough fds to open(), but having a separate notification message for > > this (like what we use for invalidation of cache), and adding not just > > an "fd" field but also "offset" and "length" fields (which would > > currently be required to be both zero to get the "full file" semantics). > > > > You mean like this? > > https://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/fuse.git/commit/?h=fuse2 Look specifically at fuse_file_map_iter(): https://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/fuse.git/tree/fs/fuse2/file.c?h=fuse2#n582 and fudev_map_ioctl(): https://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/fuse.git/tree/fs/fuse2/fudev.c?h=fuse2#n601 This avoids the security issue Jann mentioned as well as allowing arbitrary mapping of file ranges. E.g. it could also be used by a block based filesystem to map I/O directly into the block device. What the implementation lacks is any kind of caching. Since your usecase involves just one map extent per file, special casing that would be trivial. We can revisit general caching later. Thanks, Miklos
