[PATCH v4 5/6] qmp: Added new command to retrieve eBPF blob.

[Andrew Melnychenko <andrew@daynix.com>]

Added command "request-ebpf". This command returns
eBPF program encoded base64. The program taken from the
skeleton and essentially is an ELF object that can be
loaded in the future with libbpf.

The reason to use the command to provide the eBPF object
instead of a separate artifact was to avoid issues related
to finding the eBPF itself. As the eBPF maps/program should
correspond to QEMU, the eBPF cant be used from different
QEMU build.
The first solution was a helper that comes with QEMU
and loads appropriate eBPF objects. And the issue is
to find a proper helper if the system has several
different QEMUs installed and/or built from the source,
which helpers may not be compatible.
Another issue is QEMU updating while there is a running
QEMU instance. With an updated helper, it may not be
possible to hotplug virtio-net device to the already
running QEMU. Overall, requesting the eBPF object from
QEMU itself solves possible failures with very little effort.

Links:
[PATCH 3/5] qmp: Added the helper stamp check.
https://lore.kernel.org/all/20230219162100.174318-4-andrew@daynix.com/

Signed-off-by: Andrew Melnychenko <andrew@daynix.com>
---
 qapi/ebpf.json        | 58 +++++++++++++++++++++++++++++++++++++++++++
 qapi/meson.build      |  1 +
 qapi/qapi-schema.json |  1 +
 3 files changed, 60 insertions(+)
 create mode 100644 qapi/ebpf.json

diff --git a/qapi/ebpf.json b/qapi/ebpf.json
new file mode 100644
index 0000000000..3237da69a7
--- /dev/null
+++ b/qapi/ebpf.json
@@ -0,0 +1,58 @@
+# -*- Mode: Python -*-
+# vim: filetype=python
+#
+# This work is licensed under the terms of the GNU GPL, version 2 or later.
+# See the COPYING file in the top-level directory.
+
+##
+# = eBPF Objects
+##
+
+{ 'include': 'common.json' }
+
+##
+# @EbpfObject:
+#
+# Structure that holds eBPF ELF object encoded in base64.
+#
+# Since: 8.3
+#
+##
+{ 'struct': 'EbpfObject',
+  'data': {'object': 'str'},
+  'if': 'CONFIG_EBPF' }
+
+##
+# @EbpfProgramID:
+#
+# The eBPF programs that can be gotten with request-ebpf.
+#
+# @rss: Receive side scaling, technology that allows steering traffic
+# between queues by calculation hash. Users may set up indirection table
+# and hash/packet types configurations. Used with virtio-net.
+#
+# Since: 8.3
+##
+{ 'enum': 'EbpfProgramID',
+  'if': 'CONFIG_EBPF',
+  'data': [ { 'name': 'rss' } ] }
+
+##
+# @request-ebpf:
+#
+# Returns eBPF object that can be loaded with libbpf.
+# Management applications (g.e. libvirt) may load it and pass file
+# descriptors to QEMU. Which allows running QEMU without BPF capabilities.
+# It's crucial that eBPF program/map is compatible with QEMU, so it's
+# provided through QMP.
+#
+# Returns: RSS eBPF object encoded in base64.
+#
+# Since: 8.3
+#
+##
+{ 'command': 'request-ebpf',
+  'data': { 'id': 'EbpfProgramID' },
+  'returns': 'EbpfObject',
+  'if': 'CONFIG_EBPF' }
+
diff --git a/qapi/meson.build b/qapi/meson.build
index 60a668b343..90047dae1c 100644
--- a/qapi/meson.build
+++ b/qapi/meson.build
@@ -33,6 +33,7 @@ qapi_all_modules = [
   'crypto',
   'cxl',
   'dump',
+  'ebpf',
   'error',
   'introspect',
   'job',
diff --git a/qapi/qapi-schema.json b/qapi/qapi-schema.json
index 6594afba31..2c82a49bae 100644
--- a/qapi/qapi-schema.json
+++ b/qapi/qapi-schema.json
@@ -53,6 +53,7 @@
 { 'include': 'char.json' }
 { 'include': 'dump.json' }
 { 'include': 'net.json' }
+{ 'include': 'ebpf.json' }
 { 'include': 'rdma.json' }
 { 'include': 'rocker.json' }
 { 'include': 'tpm.json' }
-- 
2.40.1