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 Tue, Jul 22, 2025 at 08:00:00AM -0400, Brian Song wrote:
> On 7/20/25 12:13 PM, Stefan Hajnoczi wrote:
> > 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".
> >
> 
> It seems we are not allowed to use '_' here.
> 
> In file included from ../storage-daemon/qapi/qapi-schema.json:57:
> 
> ../storage-daemon/qapi/../../qapi/block-export.json: In struct
> 'BlockExportOptionsFuse':
> 
> ../storage-daemon/qapi/../../qapi/block-export.json:191: name of 'data'
> member '*io_uring' must not use uppercase or '_'

Then "-" is fine, but please use "io<separator>uring" so it is as close
as possible (not "uring", "iouring", etc).

Thanks,
Stefan

> 
> 
> >>
> >> 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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