qmp: Added new command to retrieve eBPF blob.

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>
Signed-off-by: Jason Wang <jasowang@redhat.com>

1 files changed, 5 insertions, 6 deletions

diff --git a/ebpf/ebpf_rss.c b/ebpf/ebpf_rss.c
index 150aa40813..2e506f9743 100644
--- a/ebpf/ebpf_rss.c
+++ b/ebpf/ebpf_rss.c
@@ -13,6 +13,8 @@
 
 #include "qemu/osdep.h"
 #include "qemu/error-report.h"
+#include "qapi/qapi-types-misc.h"
+#include "qapi/qapi-commands-ebpf.h"
 
 #include <bpf/libbpf.h>
 #include <bpf/bpf.h>
@@ -21,7 +23,7 @@
 
 #include "ebpf/ebpf_rss.h"
 #include "ebpf/rss.bpf.skeleton.h"
-#include "trace.h"
+#include "ebpf/ebpf.h"
 
 void ebpf_rss_init(struct EBPFRSSContext *ctx)
 {
@@ -53,21 +55,18 @@ static bool ebpf_rss_mmap(struct EBPFRSSContext *ctx)
                                    PROT_READ | PROT_WRITE, MAP_SHARED,
                                    ctx->map_configuration, 0);
     if (ctx->mmap_configuration == MAP_FAILED) {
-        trace_ebpf_error("eBPF RSS", "can not mmap eBPF configuration array");
         return false;
     }
     ctx->mmap_toeplitz_key = mmap(NULL, qemu_real_host_page_size(),
                                    PROT_READ | PROT_WRITE, MAP_SHARED,
                                    ctx->map_toeplitz_key, 0);
     if (ctx->mmap_toeplitz_key == MAP_FAILED) {
-        trace_ebpf_error("eBPF RSS", "can not mmap eBPF toeplitz key");
         goto toeplitz_fail;
     }
     ctx->mmap_indirections_table = mmap(NULL, qemu_real_host_page_size(),
                                    PROT_READ | PROT_WRITE, MAP_SHARED,
                                    ctx->map_indirections_table, 0);
     if (ctx->mmap_indirections_table == MAP_FAILED) {
-        trace_ebpf_error("eBPF RSS", "can not mmap eBPF indirection table");
         goto indirection_fail;
     }
 
@@ -109,14 +108,12 @@ bool ebpf_rss_load(struct EBPFRSSContext *ctx)
 
     rss_bpf_ctx = rss_bpf__open();
     if (rss_bpf_ctx == NULL) {
-        trace_ebpf_error("eBPF RSS", "can not open eBPF RSS object");
         goto error;
     }
 
     bpf_program__set_type(rss_bpf_ctx->progs.tun_rss_steering_prog, BPF_PROG_TYPE_SOCKET_FILTER);
 
     if (rss_bpf__load(rss_bpf_ctx)) {
-        trace_ebpf_error("eBPF RSS", "can not load RSS program");
         goto error;
     }
 
@@ -261,3 +258,5 @@ void ebpf_rss_unload(struct EBPFRSSContext *ctx)
     ctx->map_toeplitz_key = -1;
     ctx->map_indirections_table = -1;
 }
+
+ebpf_binary_init(EBPF_PROGRAMID_RSS, rss_bpf__elf_bytes)