Re: [PATCH RFC 0/1] block/export: FUSE-over-io_uring Support for QEMU FUSE Exports

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Wed, Jul 16, 2025 at 02:38:23PM -0400, Brian Song wrote:
> This RFC patch represents an initial implementation of the FUSE-over- 
> io_uring Exports idea proposed for Google Summer of Code (2025) under 
> the QEMU community:
> https://wiki.qemu.org/Google_Summer_of_Code_2025#FUSE-over-io_uring_exports
> 
> The implementation approach is primarily borrowed from how libfuse 
> interacts with the kernel.
> 
> FUSE-over-io_uring (https://docs.kernel.org/next/filesystems/fuse-io- 
> uring.html) has been officially merged into the Linux kernel. The idea 
> is to replace the traditional /dev/fuse based communication with a more 
> efficient io_uring-based approach. In this model, userspace registers 
> io_uring SQEs via the FUSE_IO_URING_CMD_REGISTER opcode, and then waits 
> for the kernel to forward FUSE requests as CQEs. These are processed by 
> the FUSE exports implementation in userspace and then committed back to 
> the kernel using FUSE_IO_URING_CMD_COMMIT_AND_FETCH.
> 
> To enable this feature in qemu-export-daemon, simply add the uring=on 
> option to the export configuration.

For consistency with the --blockdev file,aio=io_uring option, please
name it "io_uring=on" instead of "uring=on".

> 
> As this patch is still in the RFC stage, it currently supports **only 
> single thread**. Due to protocol requirements in FUSE-over-io_uring,
> the number of FUSE threads must match the number of CPUs. Therefore,
> this initial version only works on single-core VMs (i.e., QEMU started
> with -smp 1) or single core machine.
> 
> Brian Song (1):
>   block/export: FUSE-over-io_uring Support for QEMU FUSE Exports
> 
>  block/export/fuse.c                  | 423 +++++++++++++++++++++++++--
>  docs/tools/qemu-storage-daemon.rst   |  10 +-
>  qapi/block-export.json               |   6 +-
>  storage-daemon/qemu-storage-daemon.c |   1 +
>  util/fdmon-io_uring.c                |   5 +-
>  5 files changed, 420 insertions(+), 25 deletions(-)
> 
> -- 
> 2.50.1
> 

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