On Fri, Jun 30, 2023 at 04:21:02PM +0800, Jason Wang wrote: > On Fri, Jun 30, 2023 at 4:04 PM Daniel P. Berrangé <berra...@redhat.com> > wrote: > > > > On Fri, Jun 30, 2023 at 01:06:22PM +0800, Jason Wang wrote: > > > On Thu, Jun 15, 2023 at 6:29 AM Andrew Melnychenko <and...@daynix.com> > > > wrote: > > > > > > > > This series of patches provides the ability to retrieve eBPF program > > > > through qmp, so management application may load bpf blob with proper > > > > capabilities. > > > > Now, virtio-net devices can accept eBPF programs and maps through > > > > properties > > > > as external file descriptors. Access to the eBPF map is direct through > > > > mmap() > > > > call, so it should not require additional capabilities to bpf* calls. > > > > eBPF file descriptors can be passed to QEMU from parent process or by > > > > unix > > > > socket with sendfd() qmp command. > > > > > > > > Possible solution for libvirt may look like this: > > > > https://github.com/daynix/libvirt/tree/RSS_eBPF (WIP) > > > > > > > > Changes since v2: > > > > * moved/refactored QMP command > > > > * refactored virtio-net > > > > > > I've queued this series, but a question left: > > > > > > mmap() support for eBPF maps is not supported from day0, should we > > > fallback to syscall for the OS that doesn't support that? > > > > How recent is mmap() support ? > > I don't check. > > > Is it difficult to do a fallback ? > > Nope, but it requires privilege if we go with a syscall. > > > > > As since is a new feature, > > But it modifies the old rss loading code, no? > > - for (; i < len; ++i) { > - if (bpf_map_update_elem(ctx->map_indirections_table, &i, > - indirections_table + i, 0) < 0) { > - return false; > - } > - } > + memcpy(ctx->mmap_indirections_table, indirections_table, > + sizeof(*indirections_table) * len); > > > there's no inherant expectation of support > > for arbitrary old platforms. So only worth investing in a fallback if > > it is easy, or there's a very compelling reason to support certain > > old platforms. > > The reason is that we support eBPF RSS with syscall based map updating > in the past if Qemu was running with privilege. With this series, it > won't work if the kernel doesn't support mmap.
Oh right, yes, I missed that aspect. So yeah, we do need fallback. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
