On Wed, 29 Nov 2023 at 16:52, Amir Goldstein <amir73il@xxxxxxxxx> wrote: > direct I/O read()/write() is never a problem. > > The question is whether mmap() on a file opened with FOPEN_DIRECT_IO > when the inode is in passthrough mode, also uses fuse_passthrough_mmap()? I think it should. > or denied, similar to how mmap with ff->open_flags & FOPEN_DIRECT_IO && > vma->vm_flags & VM_MAYSHARE) && !fc->direct_io_relax > is denied? What would be the use case for FOPEN_DIRECT_IO with passthrough mmap? > A bit more challenging, because we will need to track unmounts, or at > least track > "was_cached_mmaped" state per file, but doable. Tracking unmaps via fuse_vma_close() should not be difficult. > > > > > > > Therefore, my proposal is than when filesystem is FUSE_PASSTHROUGH capable, > > > only passthrough file and cached file may be mmaped, but never allow to > > > mmap a FOPEN_DIRECT_IO file. > > > > > > Does that make sense? > > > > I'm not sure I understand how this is supposed to work. Disallowing > > mmap will break applications. > > How is this different from existing -ENODEV in fuse_file_mmap() for > !fc->direct_io_relax? What am I missing? > Is it because VM_MAYSHARE is far less common for applications? Yes, MAP_SHARE is far less common than MAP_PRIVATE. Thanks, Miklos
