From 8d836581f9b1f57ceaa2b47654754ef1260b410b Mon Sep 17 00:00:00 2001 From: Niklas Cassel Date: Wed, 16 Sep 2026 15:00:32 +0200 Subject: ata: libata-scsi: fix ata_dsm_trim_pages() kernel-doc make htmldocs fails with: Documentation/driver-api/libata:604: ./drivers/ata/libata-scsi.c:2301: ERROR: Unexpected indentation. [docutils] The Return: section of ata_dsm_trim_pages() ends its first sentence with a colon and continues with an indented bullet list. reStructuredText requires a blank line before an indented block, so docutils chokes on the list. Simply adding the missing blank line does not work either: Return: is a kernel-doc "special section", which is terminated by the first blank line, so the bullet list would end up in the Description section, detached from the sentence introducing it. Spell the two bounds out as prose instead, so that the Return: section stays self-contained. Documentation-only change. Fixes: e64e6b5dc867 ("ata: libata-scsi: scale DSM TRIM payload by MAX PAGES PER DSM COMMAND") Reported-by: Thomas Huth Closes: https://lore.kernel.org/linux-ide/b0a0b8e8-cc4f-4c7b-8bc5-fee0712d405a@redhat.com/ Reviewed-by: Damien Le Moal Reviewed-by: Thomas Huth Link: https://lore.kernel.org/r/20260916130031.29990-2-cassel@kernel.org Signed-off-by: Niklas Cassel --- .../filesystems/fuse/uapi/fuse-uapi-io-uring.rst | 126 +++++++++++++++++++++ 1 file changed, 126 insertions(+) create mode 100644 Documentation/filesystems/fuse/uapi/fuse-uapi-io-uring.rst (limited to 'Documentation/filesystems/fuse/uapi') diff --git a/Documentation/filesystems/fuse/uapi/fuse-uapi-io-uring.rst b/Documentation/filesystems/fuse/uapi/fuse-uapi-io-uring.rst new file mode 100644 index 000000000..8367be7ea --- /dev/null +++ b/Documentation/filesystems/fuse/uapi/fuse-uapi-io-uring.rst @@ -0,0 +1,126 @@ +.. SPDX-License-Identifier: GPL-2.0 + +===================================== +FUSE-over-io-uring uapi documentation +===================================== + +Commands +======== + +``enum fuse_uring_cmd``: + +``FUSE_IO_URING_CMD_ADD_QUEUE`` + Create a queue identified by ``fuse_uring_cmd_req.qid``. Queue-wide + options are passed in ``fuse_uring_cmd_req.flags``: + + ``FUSE_URING_ZERO_COPY`` + Enable zero-copy on this queue. Requires ``CAP_SYS_ADMIN`` and a buffer + pool, which is added separately via ``ADD_BUFPOOL`` before registering + entries (see `Zero-copy`_). + +``FUSE_IO_URING_CMD_ADD_BUFPOOL`` + Register the payload buffer pool for an existing queue. The server provides + a single contiguous region in ``fuse_uring_cmd_req.bufpool.uaddr`` / + ``.len``. This command must be issued after ``ADD_QUEUE`` and before + registering any payload-carrying entries on that queue. + ``fuse_uring_cmd_req.flags`` must be 0. Submitting this command with + ``IORING_URING_CMD_FIXED`` marks the pool as registered, which avoids per + i/o pinning/unpinning and mapping overhead (see `Buffer pools`_). + +``FUSE_IO_URING_CMD_REGISTER`` + Register a ring entry (a long-lived SQE that carries the request header + iovec). For a zero-copy queue, ``fuse_uring_cmd_req.ent_zero_copy_buf_index`` + indicates the reserved registered buffer table slot this entry uses for + zero-copy (see `Zero-copy`_). + +``FUSE_IO_URING_CMD_COMMIT_AND_FETCH`` + Commit the reply for a completed request and fetch the next one. The + request is identified by ``fuse_uring_cmd_req.commit_id`` (the value the + kernel reported in ``fuse_uring_ent_in_out.commit_id``). + +Structures +========== + +``struct fuse_uring_cmd_req`` (80-byte SQE command area): + +============================ ================================================== +Field Meaning +============================ ================================================== +``flags`` Command-specific flags (see each command). +``commit_id`` Request id, for ``COMMIT_AND_FETCH``. +``qid`` Queue index. +``bufpool.uaddr`` Pool base address, for ``ADD_BUFPOOL``. +``bufpool.len`` Pool length in bytes, for ``ADD_BUFPOOL``. +``bufpool.reserved`` Must be 0, for ``ADD_BUFPOOL``. +``ent_zero_copy_buf_index`` Per-entry zero-copy slot, for ``REGISTER``. +============================ ================================================== + +``struct fuse_uring_ent_in_out`` (reported by the kernel per request): + +============================ ================================================== +Field Meaning +============================ ================================================== +``flags`` ``FUSE_URING_ENT_ZERO_COPY`` if zero-copied. +``commit_id`` Id to echo back in ``COMMIT_AND_FETCH``. +``payload_sz`` Total payload size in bytes (see `Zero-copy`_). +``offset`` Payload buffer offset within the pool. +============================ ================================================== + +Buffer pools +============ +Setup: + +* Issue ``ADD_QUEUE`` for the qid. +* Issue ``ADD_BUFPOOL`` with ``bufpool.uaddr`` and ``bufpool.len`` pointing + at the region. +* Register entries with ``REGISTER``. + +For every request that has a payload, the kernel reports where the payload +lives in ``struct fuse_uring_ent_in_out`` (part of +``struct fuse_uring_req_header``): + +``offset`` + Byte offset, within the pool region, for this request's payload buffer. + The server adds this to the pool base address to locate the payload. + +``payload_sz`` + Number of payload bytes for this request. + +To use registered buffers, the server registers the pool region with io_uring +and submits ``ADD_BUFPOOL`` with ``IORING_URING_CMD_FIXED`` set in +``sqe->uring_cmd_flags`` and the index of the registered bufpool in +``sqe->buf_index``. Every SQE the server submits afterwards must follow the +same fixed-buffer protocol, carrying ``IORING_URING_CMD_FIXED`` and that same +``sqe->buf_index``. The same registered buffer can be reused for the server's +backing-store I/O as well (e.g. ``IORING_OP_READ_FIXED`` / +``IORING_OP_WRITE_FIXED``). + +Zero-copy +========= +Requirements: + +* The server must be privileged (``CAP_SYS_ADMIN``). +* A zero-copy queue: ``ADD_QUEUE`` with the ``FUSE_URING_ZERO_COPY`` flag set. +* A buffer pool: ``ADD_BUFPOOL``. +* For each entry, ``REGISTER`` with ``ent_zero_copy_buf_index`` set to the + index this entry uses in the server's io_uring registered-buffer table. + This is where the kernel registers the request's pages for the server to + access (it is separate from the payload pool). On a non-zero-copy queue this + field must be 0. + +Zero-copy is selected per open file. The server sets the open-file flag in +the ``FUSE_OPEN`` / ``FUSE_CREATE`` reply: + +``FOPEN_IO_URING_ZERO_COPY`` + Reads/writes on this open file should use zero-copy. + +For a request that is zero-copied, the kernel sets ``FUSE_URING_ENT_ZERO_COPY`` +in ``fuse_uring_ent_in_out.flags`` and places the request's pages at the +entry's ``ent_zero_copy_buf_index``. The server then issues +``IORING_OP_READ_FIXED`` / ``IORING_OP_WRITE_FIXED`` against that index to +transfer the data directly to/from the client's pages. + +For such a request, ``payload_sz`` includes the zero-copied page bytes +(transferred via the registered buffer at ``ent_zero_copy_buf_index``). Any +non-page-backed args (e.g. op headers) are still copied through the pool +payload buffer at ``offset``. -- cgit v1.3.1