qapi/block-export: Document FUSE's multi-threading

Document for users that FUSE's multi-threading implementation
distributes requests in a round-robin manner, regardless of where they
originate from.

As noted by Stefan, this will probably change with a FUSE-over-io_uring
implementation (which is supposed to have CPU affinity), but documenting
that is left for once that is done.

Suggested-by: Stefan Hajnoczi <stefanha@redhat.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Hanna Czenczek <hreitz@redhat.com>
Message-ID: <20260309150856.26800-25-hreitz@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

diff --git a/qapi/block-export.json b/qapi/block-export.json
index 160cd2e3ca07a89bca1d571c8bdb22a532dcd671..dd724acf1cbc8dca87744af1303bba8c9c5dad43 100644 (file)
--- a/qapi/block-export.json
+++ b/qapi/block-export.json
@@ -164,6 +164,11 @@
 # Options for exporting a block graph node on some (file) mountpoint
 # as a raw image.
 #
+# Multi-threading note: The FUSE export supports multi-threading.
+# Currently, requests are distributed across these threads in a
+# round-robin fashion, i.e. independently of the CPU core from which a
+# request originates.
+#
 # @mountpoint: Path on which to export the block device via FUSE.
 #     This must point to an existing regular file.
 #