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Re: [PATCH v7 4/5] qmp: Added new command to retrieve eBPF blob.


From: Yuri Benditovich
Subject: Re: [PATCH v7 4/5] qmp: Added new command to retrieve eBPF blob.
Date: Mon, 18 Dec 2023 15:24:57 +0200



On Mon, Dec 18, 2023 at 2:54 PM Markus Armbruster <armbru@redhat.com> wrote:
Uh, I missed this one, my apologies!  Let me have a quick look...

Commit message style nitpick:

    qmp: Add command to retrieve eBPF blob

or

    qmp: New command to retrieve eBPF blob

It's a title, not a sentence.

Andrew Melnychenko <andrew@daynix.com> writes:

> Now, the binary objects may be retrieved by id.
> It would require for future qmp commands that may require specific
> eBPF blob.
>
> 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. eBPF object is an ELF binary
> that contains the eBPF program and eBPF map description(BTF).
> Overall, eBPF object should contain the program and enough
> metadata to create/load eBPF with libbpf. As the eBPF
> maps/program should correspond to QEMU, the eBPF can't
> 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 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>

[...]

> diff --git a/qapi/ebpf.json b/qapi/ebpf.json
> new file mode 100644
> index 0000000000..ba78407148
> --- /dev/null
> +++ b/qapi/ebpf.json
> @@ -0,0 +1,66 @@
> +# -*- 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
> +#
> +# eBPF object is an ELF binary that contains the eBPF
> +# program and eBPF map description(BTF). Overall, eBPF
> +# object should contain the program and enough metadata
> +# to create/load eBPF with libbpf. As the eBPF maps/program
> +# should correspond to QEMU, the eBPF can't be used from
> +# different QEMU build.

An introduction, nice!

Two spaces between sentences for consistency, please.

Wrap comment lines at column 70, like this:

   # eBPF object is an ELF binary that contains the eBPF program and eBPF
   # map description(BTF).  Overall, eBPF object should contain the
   # program and enough metadata to create/load eBPF with libbpf.  As the
   # eBPF maps/program should correspond to QEMU, the eBPF can't be used
   # from different QEMU build.

> +#
> +# Currently, there is a possible eBPF for receive-side scaling (RSS).
> +#
> +##
> +
> +##
> +# @EbpfObject:
> +#
> +# An eBPF ELF object.
> +#
> +# @object: the eBPF object encoded in base64
> +#
> +# Since: 8.2

Won't make 8.2, so bump to 9.0.  More of the same below, not noting it
again.

Will there be 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: 8.2
> +##
> +{ 'enum': 'EbpfProgramID',
> +  'if': 'CONFIG_EBPF',
> +  'data': [ { 'name': 'rss' } ] }
> +
> +##
> +# @request-ebpf:
> +#
> +# Retrieve an eBPF object that can be loaded with libbpf.  Management
> +# applications (g.e. libvirt) may load it and pass file descriptors to
> +# QEMU, so they can run running QEMU without BPF capabilities.
> +#
> +# @id: The ID of the program to return.
> +#
> +# Returns: eBPF object encoded in base64.
> +#
> +# Since: 8.2
> +##
> +{ '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' }

With the (minor) doc comment fixes:
Acked-by: Markus Armbruster <armbru@redhat.com>


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