diff options
Diffstat (limited to 'Documentation/filesystems/fuse/fuse-io-uring.rst')
| -rw-r--r-- | Documentation/filesystems/fuse/fuse-io-uring.rst | 36 |
1 files changed, 34 insertions, 2 deletions
diff --git a/Documentation/filesystems/fuse/fuse-io-uring.rst b/Documentation/filesystems/fuse/fuse-io-uring.rst index d73dd0dbd238..29f98057500d 100644 --- a/Documentation/filesystems/fuse/fuse-io-uring.rst +++ b/Documentation/filesystems/fuse/fuse-io-uring.rst @@ -11,6 +11,9 @@ 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. +For the userspace protocol, see +Documentation/filesystems/fuse/uapi/fuse-uapi-io-uring.rst. + Limitations =========== As of now not all requests types are supported through io-uring, userspace @@ -95,5 +98,34 @@ Sending requests with CQEs | <fuse_unlink() | | <sys_unlink() | - - +Buffer pools +============ + +Without a buffer pool, every entry needs to pass a dedicated payload buffer +large enough for the maximum payload size. A buffer pool decouples entries +from payload buffers. The server hands the kernel one contiguous buffer pool +of memory and when the kernel sends the server a request, it indicates the +offset into the pool for that request's payload. Internally, the kernel is +able to manage/optimize the buffer pool memory however it likes. + +A server may also register the pool region with io_uring as a fixed buffer. +The backing pages are then pinned once, avoiding per-request pinning and +address translation. This also allows servers to use the same registered +buffers for subsequent backing store I/O through io-uring, keeping data +in the same pinned pages without additional pinning / mapping overhead. + +Zero-copy +========= + +Zero-copy lets the server read from / write to the client's pages (pinned +user pages for direct I/O, or page-cache folios for buffered I/O) without an +intermediary payload copy. This requires CAP_SYS_ADMIN privileges. + +When a fuse request arrives for a file that opted into zero-copy, the kernel +registers the relevant pages (pinned user pages for direct i/o or underlying +page cache folios for buffered i/o) into a sparse slot in the server's +io_uring registered buffer table. The server can then operate on these pages +directly using io-uring fixed buffer operations (eg read_fixed / write_fixed) +and the kernel unregisters these pages when the request completes. +Non-page-backed args (eg op out headers) will go through the payload buffer as +normal. |