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

["Daniel P. Berrangé" <berrange@redhat.com>]

On Mon, May 01, 2023 at 10:21:00AM +0300, Andrew Melnychenko wrote:
> 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.
> 
> Signed-off-by: Andrew Melnychenko <andrew@daynix.com>
> ---
>  monitor/qmp-cmds.c | 16 ++++++++++++++++
>  qapi/misc.json     | 28 ++++++++++++++++++++++++++++
>  2 files changed, 44 insertions(+)
> 
> diff --git a/monitor/qmp-cmds.c b/monitor/qmp-cmds.c
> index b0f948d3376..f7641bb55b9 100644
> --- a/monitor/qmp-cmds.c
> +++ b/monitor/qmp-cmds.c
> @@ -32,6 +32,7 @@
>  #include "hw/mem/memory-device.h"
>  #include "hw/intc/intc.h"
>  #include "hw/rdma/rdma.h"
> +#include "ebpf/ebpf.h"
>  
>  NameInfo *qmp_query_name(Error **errp)
>  {
> @@ -209,3 +210,18 @@ static void __attribute__((__constructor__)) monitor_init_qmp_commands(void)
>                           qmp_marshal_qmp_capabilities,
>                           QCO_ALLOW_PRECONFIG, 0);
>  }
> +
> +EbpfObject *qmp_request_ebpf(const char *id, Error **errp)
> +{
> +    EbpfObject *ret = NULL;
> +    size_t size = 0;
> +    const void *data = ebpf_find_binary_by_id(id, &size, errp);
> +    if (!data) {
> +        return NULL;
> +    }
> +
> +    ret = g_new0(EbpfObject, 1);
> +    ret->object = g_base64_encode(data, size);
> +
> +    return ret;
> +}
> diff --git a/qapi/misc.json b/qapi/misc.json
> index 6ddd16ea283..81613fd1b13 100644
> --- a/qapi/misc.json
> +++ b/qapi/misc.json
> @@ -618,3 +618,31 @@
>  { 'event': 'VFU_CLIENT_HANGUP',
>    'data': { 'vfu-id': 'str', 'vfu-qom-path': 'str',
>              'dev-id': 'str', 'dev-qom-path': 'str' } }
> +
> +##
> +# @EbpfObject:
> +#
> +# Structure that holds eBPF ELF object encoded in base64.
> +#
> +# Since: 8.1
> +#
> +##
> +{ 'struct': 'EbpfObject',
> +  'data': {'object': 'str'} }
> +
> +##
> +# @request-ebpf:
> +#
> +# Function 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.
> +#
> +# Returns: RSS eBPF object encoded in base64.
> +#
> +# Since: 8.1
> +#
> +##
> +{ 'command': 'request-ebpf',
> +  'data': { 'id': 'str' },

Since the number of EBPF program IDs is finite and known at build
time, I think we'd be better using an enum instead of str. That
will let apps introspect the QAPI schema to query whether the
particular EBPF program ID is known to this version fo QEMU.

> +  'returns': 'EbpfObject' }
> +
> -- 
> 2.39.1
> 

With regards,
Daniel
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