On Sun, 18 Nov 2018 at 06:13, Y Song <ys114321@xxxxxxxxx> wrote: > > There is a slight change of user space behavior for this patch. > Without this patch, the value bpf_attr.test.data_size_out is output only. > For example, > output buffer : out_buf (user allocated size 10) > data_size_out is a random value (e.g., 1), > > The actual data to copy is 5. > > In today's implementation, the kernel will copy 5 and set data_size_out is 5. > > With this patch, the kernel will copy 1 and set data_size_out is 5. > > I am not 100% sure at this time whether we CAN overload data_size_out > since it MAY break existing applications. Yes, that's correct. I think that the likelihood of this is low. It would affect code that uses bpf_attr without zeroing it first. I had a look around, and I could only find code that would keep working: * kernel libbpf and descendants (e.g katran) * github.com/iovisor/gobpf * github.com/newtools/ebpf That doesn't really guarantee anything of course. -- Lorenz Bauer | Systems Engineer 25 Lavington St., London SE1 0NZ www.cloudflare.com
