This patch adds a new storage export option for storage-export-daemon
to enable FUSE-over-io_uring via 'io-uring=on|off' (default: off).

The initialization phase performs a protocol handshake via the legacy
/dev/fuse interface before transitioning to the io_uring mode.
If multiple IOThreads are configured, the export distributes the uring
queues to handle requests concurrently.

Suggested-by: Kevin Wolf <kwolf@redhat.com>
Suggested-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Brian Song <hibriansong@gmail.com>
---
 block/export/fuse.c                  | 3 +--
 docs/tools/qemu-storage-daemon.rst   | 7 +++++--
 qapi/block-export.json               | 5 ++++-
 storage-daemon/qemu-storage-daemon.c | 1 +
 4 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/block/export/fuse.c b/block/export/fuse.c
index abae83041b..09642ccf5a 100644
--- a/block/export/fuse.c
+++ b/block/export/fuse.c
@@ -587,8 +587,7 @@ static int fuse_export_create(BlockExport *blk_exp,
     assert(blk_exp_args->type == BLOCK_EXPORT_TYPE_FUSE);

 #ifdef CONFIG_LINUX_IO_URING
-    /* TODO Add FUSE-over-io_uring Option */
-    exp->is_uring = false;
+    exp->is_uring = args->io_uring;
     exp->uring_queue_depth = FUSE_DEFAULT_URING_QUEUE_DEPTH;
 #else
     if (args->io_uring) {
diff --git a/docs/tools/qemu-storage-daemon.rst b/docs/tools/qemu-storage-daemon.rst
index 35ab2d7807..ad0f41a78f 100644
--- a/docs/tools/qemu-storage-daemon.rst
+++ b/docs/tools/qemu-storage-daemon.rst
@@ -78,7 +78,7 @@ Standard options:
 .. option:: --export [type=]nbd,id=<id>,node-name=<node-name>[,name=<export-name>][,writable=on|off][,bitmap=<name>]
   --export [type=]vhost-user-blk,id=<id>,node-name=<node-name>,addr.type=unix,addr.path=<socket-path>[,writable=on|off][,logical-block-size=<block-size>][,num-queues=<num-queues>]
   --export [type=]vhost-user-blk,id=<id>,node-name=<node-name>,addr.type=fd,addr.str=<fd>[,writable=on|off][,logical-block-size=<block-size>][,num-queues=<num-queues>]
-  --export [type=]fuse,id=<id>,node-name=<node-name>,mountpoint=<file>[,growable=on|off][,writable=on|off][,allow-other=on|off|auto]
+  --export [type=]fuse,id=<id>,node-name=<node-name>,mountpoint=<file>[,growable=on|off][,writable=on|off][,allow-other=on|off|auto][,io-uring=on|off]
   --export [type=]vduse-blk,id=<id>,node-name=<node-name>,name=<vduse-name>[,writable=on|off][,num-queues=<num-queues>][,queue-size=<queue-size>][,logical-block-size=<block-size>][,serial=<serial-number>]

   is a block export definition. ``node-name`` is the block node that should be
@@ -111,7 +111,10 @@ Standard options:
   that enabling this option as a non-root user requires enabling the
   user_allow_other option in the global fuse.conf configuration file.  Setting
   ``allow-other`` to auto (the default) will try enabling this option, and on
-  error fall back to disabling it.
+  error fall back to disabling it. Once ``io-uring`` is enabled (off by default),
+  the FUSE-over-io_uring-related settings will be initialized to bypass the
+  traditional /dev/fuse communication mechanism and instead use io_uring to
+  handle FUSE operations.

   The ``vduse-blk`` export type takes a ``name`` (must be unique across the host)
   to create the VDUSE device.
diff --git a/qapi/block-export.json b/qapi/block-export.json
index 9ae703ad01..37f2fc47e2 100644
--- a/qapi/block-export.json
+++ b/qapi/block-export.json
@@ -184,12 +184,15 @@
 #     mount the export with allow_other, and if that fails, try again
 #     without.  (since 6.1; default: auto)
 #
+# @io-uring: Use FUSE-over-io-uring.  (since 10.2; default: false)
+#
 # Since: 6.0
 ##
 { 'struct': 'BlockExportOptionsFuse',
   'data': { 'mountpoint': 'str',
             '*growable': 'bool',
-            '*allow-other': 'FuseExportAllowOther' },
+            '*allow-other': 'FuseExportAllowOther',
+            '*io-uring': 'bool' },
   'if': 'CONFIG_FUSE' }

 ##
diff --git a/storage-daemon/qemu-storage-daemon.c b/storage-daemon/qemu-storage-daemon.c
index eb72561358..0cd4cd2b58 100644
--- a/storage-daemon/qemu-storage-daemon.c
+++ b/storage-daemon/qemu-storage-daemon.c
@@ -107,6 +107,7 @@ static void help(void)
 #ifdef CONFIG_FUSE
 "  --export [type=]fuse,id=<id>,node-name=<node-name>,mountpoint=<file>\n"
 "           [,growable=on|off][,writable=on|off][,allow-other=on|off|auto]\n"
+"           [,io-uring=on|off]"
 "                         export the specified block node over FUSE\n"
 "\n"
 #endif /* CONFIG_FUSE */
--
2.43.0

Brian Song <hibriansong@gmail.com> writes:

> This patch adds a new storage export option for storage-export-daemon
> to enable FUSE-over-io_uring via 'io-uring=on|off' (default: off).
>
> The initialization phase performs a protocol handshake via the legacy
> /dev/fuse interface before transitioning to the io_uring mode.
> If multiple IOThreads are configured, the export distributes the uring
> queues to handle requests concurrently.
>
> Suggested-by: Kevin Wolf <kwolf@redhat.com>
> Suggested-by: Stefan Hajnoczi <stefanha@redhat.com>
> Signed-off-by: Brian Song <hibriansong@gmail.com>

[...]

> diff --git a/qapi/block-export.json b/qapi/block-export.json
> index 9ae703ad01..37f2fc47e2 100644
> --- a/qapi/block-export.json
> +++ b/qapi/block-export.json
> @@ -184,12 +184,15 @@
>  #     mount the export with allow_other, and if that fails, try again
>  #     without.  (since 6.1; default: auto)
>  #
> +# @io-uring: Use FUSE-over-io-uring.  (since 10.2; default: false)

since 11.0

> +#
>  # Since: 6.0
>  ##
>  { 'struct': 'BlockExportOptionsFuse',
>    'data': { 'mountpoint': 'str',
>              '*growable': 'bool',
> -            '*allow-other': 'FuseExportAllowOther' },
> +            '*allow-other': 'FuseExportAllowOther',
> +            '*io-uring': 'bool' },
>    'if': 'CONFIG_FUSE' }
>
>  ##

With that
Acked-by: Markus Armbruster <armbru@redhat.com>

[...]