On Sat, Feb 25, 2023 at 2:59 AM Daniel Rosenberg via Lsf-pc <lsf-pc@xxxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > > On Fri, Feb 10, 2023 at 7:52 AM Miklos Szeredi <miklos@xxxxxxxxxx> wrote: > > > > Several fuse based filesystems pass file data from an underlying > > filesystem without modification. The added value can come from > > changed directory structure, changed metadata or the ability to > > intercept I/O only in special cases. This pattern is very common, so > > optimizing it could be very worthwhile. > > > > I'd like to discuss proposed solutions to enabling data passthrough. > > There are several prototypes: > > > > - fuse2[1] (myself, very old) > > - fuse-passthrough[2] (Alessio Balsini, more recent) > > - fuse-bpf[3] (Daniel Rosenberg, new) > > > > The scope of fuse-bpf is much wider, but it does offer conditional > > passthrough behavior as well. > > > > One of the questions is how to reference underlying files. Passing > > open file descriptors directly in the fuse messages could be > > dangerous[4]. Setting up the mapping from an open file descriptor to > > the kernel using an ioctl() instead should be safe. > > > > Other open issues: > > > > - what shall be the lifetime of the mapping? > > > > - does the mapped open file need to be visible to userspace? > > Remember, this is a kernel module, so there's no process involved > > where you could look at /proc/PID/fd. Adding a kernel thread for each > > fuse instance that installs these mapped fds as actual file descriptor > > might be the solution. > > > > Thanks, > > Miklos > > > > > > [1] https://lore.kernel.org/all/CAJfpegtjEoE7H8tayLaQHG9fRSBiVuaspnmPr2oQiOZXVB1+7g@xxxxxxxxxxxxxx/ > > > > [2] https://lore.kernel.org/all/20210125153057.3623715-1-balsini@xxxxxxxxxxx/ > > > > [3] https://lore.kernel.org/all/20221122021536.1629178-1-drosen@xxxxxxxxxx/ > > > > [4] https://lore.kernel.org/all/CAG48ez17uXtjCTa7xpa=JWz3iBbNDQTKO2hvn6PAZtfW3kXgcA@xxxxxxxxxxxxxx/ > > I'd be very interested to discuss fuse-bpf, and how it aligns with the > other efforts. I recall there being some io uring effort as well, > though I haven't looked into that too much yet. > For the record, I scheduled a (30 min) session for this with you and Miklos co-leads. Bernd's session on FUSE uring will follow right after. Thanks, Amir.
