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

[Markus Armbruster <armbru@redhat.com>]

Andrew Melnychenko <andrew@daynix.com> writes:

> 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

can't

> QEMU build.

Blank line between paragaphs.

> 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.

Blank line between paragaphs.

> 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.

I respectfully disagree with "very little".  But it's your commit
message, not mine.  "Acceptable 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' }
> +

Trim the trailing blank line.

Terminology: you use "eBPF program" and "eBPF object".  What's the
difference?  If there's none, use only one term, please.  To me,
"program" feels more clear.

> 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' }