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Merge tag 'fuse-update-6.14' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/fuse
Pull fuse updates from Miklos Szeredi: "Add support for io-uring communication between kernel and userspace using IORING_OP_URING_CMD (Bernd Schubert). Following features enable gains in performance compared to the regular interface: - Allow processing multiple requests with less syscall overhead - Combine commit of old and fetch of new fuse request - CPU/NUMA affinity of queues Patches were reviewed by several people, including Pavel Begunkov, io-uring co-maintainer" * tag 'fuse-update-6.14' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/fuse: fuse: prevent disabling io-uring on active connections fuse: enable fuse-over-io-uring fuse: block request allocation until io-uring init is complete fuse: {io-uring} Prevent mount point hang on fuse-server termination fuse: Allow to queue bg requests through io-uring fuse: Allow to queue fg requests through io-uring fuse: {io-uring} Make fuse_dev_queue_{interrupt,forget} non-static fuse: {io-uring} Handle teardown of ring entries fuse: Add io-uring sqe commit and fetch support fuse: {io-uring} Make hash-list req unique finding functions non-static fuse: Add fuse-io-uring handling into fuse_copy fuse: Make fuse_copy non static fuse: {io-uring} Handle SQEs - register commands fuse: make args->in_args[0] to be always the header fuse: Add fuse-io-uring design documentation fuse: Move request bits fuse: Move fuse_get_dev to header file fuse: rename to fuse_dev_end_requests and make non-static
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‎Documentation/filesystems/fuse-io-uring.rst‎

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.. SPDX-License-Identifier: GPL-2.0
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=======================================
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FUSE-over-io-uring design documentation
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=======================================
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This documentation covers basic details how the fuse
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kernel/userspace communication through io-uring is configured
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and works. For generic details about FUSE see fuse.rst.
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This document also covers the current interface, which is
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still in development and might change.
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Limitations
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===========
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As of now not all requests types are supported through io-uring, userspace
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is required to also handle requests through /dev/fuse after io-uring setup
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is complete. Specifically notifications (initiated from the daemon side)
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and interrupts.
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Fuse io-uring configuration
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===========================
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Fuse kernel requests are queued through the classical /dev/fuse
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read/write interface - until io-uring setup is complete.
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In order to set up fuse-over-io-uring fuse-server (user-space)
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needs to submit SQEs (opcode = IORING_OP_URING_CMD) to the /dev/fuse
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connection file descriptor. Initial submit is with the sub command
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FUSE_URING_REQ_REGISTER, which will just register entries to be
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available in the kernel.
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Once at least one entry per queue is submitted, kernel starts
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to enqueue to ring queues.
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Note, every CPU core has its own fuse-io-uring queue.
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Userspace handles the CQE/fuse-request and submits the result as
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subcommand FUSE_URING_REQ_COMMIT_AND_FETCH - kernel completes
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the requests and also marks the entry available again. If there are
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pending requests waiting the request will be immediately submitted
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to the daemon again.
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Initial SQE
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-----------::
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| | FUSE filesystem daemon
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| |
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| | >io_uring_submit()
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| | IORING_OP_URING_CMD /
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| | FUSE_URING_CMD_REGISTER
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| | [wait cqe]
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| | >io_uring_wait_cqe() or
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| | >io_uring_submit_and_wait()
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| |
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| >fuse_uring_cmd() |
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| >fuse_uring_register() |
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Sending requests with CQEs
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--------------------------::
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| | FUSE filesystem daemon
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| | [waiting for CQEs]
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| "rm /mnt/fuse/file" |
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| |
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| >sys_unlink() |
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| >fuse_unlink() |
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| [allocate request] |
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| >fuse_send_one() |
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| ... |
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| >fuse_uring_queue_fuse_req |
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| [queue request on fg queue] |
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| >fuse_uring_add_req_to_ring_ent() |
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| ... |
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| >fuse_uring_copy_to_ring() |
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| >io_uring_cmd_done() |
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| >request_wait_answer() |
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| [sleep on req->waitq] |
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| | [receives and handles CQE]
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| | [submit result and fetch next]
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| | >io_uring_submit()
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| | IORING_OP_URING_CMD/
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| | FUSE_URING_CMD_COMMIT_AND_FETCH
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| >fuse_uring_cmd() |
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| >fuse_uring_commit_fetch() |
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| >fuse_uring_commit() |
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| >fuse_uring_copy_from_ring() |
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| [ copy the result to the fuse req] |
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| >fuse_uring_req_end() |
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| >fuse_request_end() |
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| [wake up req->waitq] |
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| >fuse_uring_next_fuse_req |
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| [wait or handle next req] |
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| |
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| [req->waitq woken up] |
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| <fuse_unlink() |
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| <sys_unlink() |
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‎Documentation/filesystems/index.rst‎

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hpfs
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fuse
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fuse-io
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fuse-io-uring
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inotify
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isofs
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nilfs2

‎fs/fuse/Kconfig‎

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to be performed directly on a backing file.
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If you want to allow passthrough operations, answer Y.
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config FUSE_IO_URING
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bool "FUSE communication over io-uring"
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default y
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depends on FUSE_FS
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depends on IO_URING
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help
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This allows sending FUSE requests over the io-uring interface and
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also adds request core affinity.
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If you want to allow fuse server/client communication through io-uring,
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answer Y

‎fs/fuse/Makefile‎

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fuse-$(CONFIG_FUSE_DAX) += dax.o
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fuse-$(CONFIG_FUSE_PASSTHROUGH) += passthrough.o
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fuse-$(CONFIG_SYSCTL) += sysctl.o
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fuse-$(CONFIG_FUSE_IO_URING) += dev_uring.o
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virtiofs-y := virtio_fs.o

‎fs/fuse/dax.c‎

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args.opcode = FUSE_REMOVEMAPPING;
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args.nodeid = fi->nodeid;
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args.in_numargs = 2;
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args.in_args[0].size = sizeof(*inargp);
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args.in_args[0].value = inargp;
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args.in_args[1].size = inargp->count * sizeof(*remove_one);
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args.in_args[1].value = remove_one;
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args.in_numargs = 3;
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fuse_set_zero_arg0(&args);
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args.in_args[1].size = sizeof(*inargp);
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args.in_args[1].value = inargp;
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args.in_args[2].size = inargp->count * sizeof(*remove_one);
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args.in_args[2].value = remove_one;
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return fuse_simple_request(fm, &args);
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}
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