[Add several documentation updates I had missed after
renaming functions and also fixes 'make htmldocs'.]
Signed-off-by: Bernd Schubert <bschubert@xxxxxxx>
Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
---
Documentation/filesystems/fuse-io-uring.rst | 99 +++++++++++++++++++++++++++++
Documentation/filesystems/index.rst | 1 +
2 files changed, 100 insertions(+)
diff --git a/Documentation/filesystems/fuse-io-uring.rst b/Documentation/filesystems/fuse-io-uring.rst
new file mode 100644
index 0000000000000000000000000000000000000000..d73dd0dbd2381639320f5bb59a2fec95e06928b8
--- /dev/null
+++ b/Documentation/filesystems/fuse-io-uring.rst
@@ -0,0 +1,99 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=======================================
+FUSE-over-io-uring design documentation
+=======================================
+
+This documentation covers basic details how the fuse
+kernel/userspace communication through io-uring is configured
+and works. For generic details about FUSE see fuse.rst.
+
+This document also covers the current interface, which is
+still in development and might change.
+
+Limitations
+===========
+As of now not all requests types are supported through io-uring, userspace
+is required to also handle requests through /dev/fuse after io-uring setup
+is complete. Specifically notifications (initiated from the daemon side)
+and interrupts.
+
+Fuse io-uring configuration
+===========================
+
+Fuse kernel requests are queued through the classical /dev/fuse
+read/write interface - until io-uring setup is complete.
+
+In order to set up fuse-over-io-uring fuse-server (user-space)
+needs to submit SQEs (opcode = IORING_OP_URING_CMD) to the /dev/fuse
+connection file descriptor. Initial submit is with the sub command
+FUSE_URING_REQ_REGISTER, which will just register entries to be
+available in the kernel.
+
+Once at least one entry per queue is submitted, kernel starts
+to enqueue to ring queues.
+Note, every CPU core has its own fuse-io-uring queue.
+Userspace handles the CQE/fuse-request and submits the result as
+subcommand FUSE_URING_REQ_COMMIT_AND_FETCH - kernel completes
+the requests and also marks the entry available again. If there are
+pending requests waiting the request will be immediately submitted
+to the daemon again.
+
+Initial SQE
+-----------::
+
+ | | FUSE filesystem daemon
+ | |
+ | | >io_uring_submit()
+ | | IORING_OP_URING_CMD /
+ | | FUSE_URING_CMD_REGISTER
+ | | [wait cqe]
+ | | >io_uring_wait_cqe() or
+ | | >io_uring_submit_and_wait()
+ | |
+ | >fuse_uring_cmd() |
+ | >fuse_uring_register() |
+
+
+Sending requests with CQEs
+--------------------------::
+
+ | | FUSE filesystem daemon
+ | | [waiting for CQEs]
+ | "rm /mnt/fuse/file" |
+ | |
+ | >sys_unlink() |
+ | >fuse_unlink() |
+ | [allocate request] |
+ | >fuse_send_one() |
+ | ... |
+ | >fuse_uring_queue_fuse_req |
+ | [queue request on fg queue] |
+ | >fuse_uring_add_req_to_ring_ent() |
+ | ... |
+ | >fuse_uring_copy_to_ring() |
+ | >io_uring_cmd_done() |
+ | >request_wait_answer() |
+ | [sleep on req->waitq] |
+ | | [receives and handles CQE]
+ | | [submit result and fetch next]
+ | | >io_uring_submit()
+ | | IORING_OP_URING_CMD/
+ | | FUSE_URING_CMD_COMMIT_AND_FETCH
+ | >fuse_uring_cmd() |
+ | >fuse_uring_commit_fetch() |
+ | >fuse_uring_commit() |
+ | >fuse_uring_copy_from_ring() |
+ | [ copy the result to the fuse req] |
+ | >fuse_uring_req_end() |
+ | >fuse_request_end() |
+ | [wake up req->waitq] |
+ | >fuse_uring_next_fuse_req |
+ | [wait or handle next req] |
+ | |
+ | [req->waitq woken up] |
+ | <fuse_unlink() |
+ | <sys_unlink() |
+
+
+
diff --git a/Documentation/filesystems/index.rst b/Documentation/filesystems/index.rst
index 44e9e77ffe0d4b9c85f9921190d33dfd21acff8f..2636f2a41bd3d38eef7fef74f46dade8c2beaeac 100644
--- a/Documentation/filesystems/index.rst
+++ b/Documentation/filesystems/index.rst
@@ -98,6 +98,7 @@ Documentation for filesystem implementations.
hpfs
fuse
fuse-io
+ fuse-io-uring
inotify
isofs
nilfs2
--
2.43.0
