On Thu, Oct 31, 2019 at 11:19:21AM -0700, Alexei Starovoitov wrote: > On Thu, Oct 31, 2019 at 10:42 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote: > > > > On Thu, Oct 31, 2019 at 08:17:43AM -0700, Alexei Starovoitov wrote: > > > On Thu, Oct 31, 2019 at 7:52 AM Toke Høiland-Jørgensen <toke@xxxxxxxxxx> wrote: > > > > > > > > Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> writes: > > > > > > > > > On Thu, Oct 31, 2019 at 7:26 AM Toke Høiland-Jørgensen <toke@xxxxxxxxxx> wrote: > > > > >> > > > > >> Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> writes: > > > > >> > > > > >> > On Thu, Oct 31, 2019 at 7:13 AM Toke Høiland-Jørgensen <toke@xxxxxxxxxx> wrote: > > > > >> >> > > > > >> >> Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> writes: > > > > >> >> > > > > >> >> > On Thu, Oct 31, 2019 at 1:03 AM Björn Töpel <bjorn.topel@xxxxxxxxx> wrote: > > > > >> >> >> > > > > >> >> >> On Thu, 31 Oct 2019 at 08:17, Magnus Karlsson <magnus.karlsson@xxxxxxxxx> wrote: > > > > >> >> >> > > > > > >> >> >> > On Wed, Oct 30, 2019 at 2:36 PM Toke Høiland-Jørgensen <toke@xxxxxxxxxx> wrote: > > > > >> >> >> > > > > > > >> >> >> > > Magnus Karlsson <magnus.karlsson@xxxxxxxxx> writes: > > > > >> >> >> > > > > > > >> >> >> > > > When the need_wakeup flag was added to AF_XDP, the format of the > > > > >> >> >> > > > XDP_MMAP_OFFSETS getsockopt was extended. Code was added to the > > > > >> >> >> > > > kernel to take care of compatibility issues arrising from running > > > > >> >> >> > > > applications using any of the two formats. However, libbpf was > > > > >> >> >> > > > not extended to take care of the case when the application/libbpf > > > > >> >> >> > > > uses the new format but the kernel only supports the old > > > > >> >> >> > > > format. This patch adds support in libbpf for parsing the old > > > > >> >> >> > > > format, before the need_wakeup flag was added, and emulating a > > > > >> >> >> > > > set of static need_wakeup flags that will always work for the > > > > >> >> >> > > > application. > > > > >> >> >> > > > > > > >> >> >> > > Hi Magnus > > > > >> >> >> > > > > > > >> >> >> > > While you're looking at backwards compatibility issues with xsk: libbpf > > > > >> >> >> > > currently fails to compile on a system that has old kernel headers > > > > >> >> >> > > installed (this is with kernel-headers 5.3): > > > > >> >> >> > > > > > > >> >> >> > > $ echo "#include <bpf/xsk.h>" | gcc -x c - > > > > >> >> >> > > In file included from <stdin>:1: > > > > >> >> >> > > /usr/include/bpf/xsk.h: In function ‘xsk_ring_prod__needs_wakeup’: > > > > >> >> >> > > /usr/include/bpf/xsk.h:82:21: error: ‘XDP_RING_NEED_WAKEUP’ undeclared (first use in this function) > > > > >> >> >> > > 82 | return *r->flags & XDP_RING_NEED_WAKEUP; > > > > >> >> >> > > | ^~~~~~~~~~~~~~~~~~~~ > > > > >> >> >> > > /usr/include/bpf/xsk.h:82:21: note: each undeclared identifier is reported only once for each function it appears in > > > > >> >> >> > > /usr/include/bpf/xsk.h: In function ‘xsk_umem__extract_addr’: > > > > >> >> >> > > /usr/include/bpf/xsk.h:173:16: error: ‘XSK_UNALIGNED_BUF_ADDR_MASK’ undeclared (first use in this function) > > > > >> >> >> > > 173 | return addr & XSK_UNALIGNED_BUF_ADDR_MASK; > > > > >> >> >> > > | ^~~~~~~~~~~~~~~~~~~~~~~~~~~ > > > > >> >> >> > > /usr/include/bpf/xsk.h: In function ‘xsk_umem__extract_offset’: > > > > >> >> >> > > /usr/include/bpf/xsk.h:178:17: error: ‘XSK_UNALIGNED_BUF_OFFSET_SHIFT’ undeclared (first use in this function) > > > > >> >> >> > > 178 | return addr >> XSK_UNALIGNED_BUF_OFFSET_SHIFT; > > > > >> >> >> > > | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > > > >> >> >> > > > > > > >> >> >> > > > > > > >> >> >> > > > > > > >> >> >> > > How would you prefer to handle this? A patch like the one below will fix > > > > >> >> >> > > the compile errors, but I'm not sure it makes sense semantically? > > > > >> >> >> > > > > > >> >> >> > Thanks Toke for finding this. Of course it should be possible to > > > > >> >> >> > compile this on an older kernel, but without getting any of the newer > > > > >> >> >> > functionality that is not present in that older kernel. > > > > >> >> >> > > > > >> >> >> Is the plan to support source compatibility for the headers only, or > > > > >> >> >> the whole the libbpf itself? Is the usecase here, that you've built > > > > >> >> >> libbpf.so with system headers X, and then would like to use the > > > > >> >> >> library on a system with older system headers X~10? XDP sockets? BTF? > > > > >> >> > > > > > >> >> > libbpf has to be backward and forward compatible. > > > > >> >> > Once compiled it has to run on older and newer kernels. > > > > >> >> > Conditional compilation is not an option obviously. > > > > >> >> > > > > >> >> So what do we do, then? Redefine the constants in libbpf/xsh.h if > > > > >> >> they're not in the kernel header file? > > > > >> > > > > > >> > why? How and whom it will help? > > > > >> > To libbpf.rpm creating person or to end user? > > > > >> > > > > >> Anyone who tries to compile a new libbpf against an older kernel. You're > > > > >> saying yourself that "libbpf has to be backward and forward compatible". > > > > >> Surely that extends to compile time as well as runtime? > > > > > > > > > > how old that older kernel? > > > > > Does it have up-to-date bpf.h in /usr/include ? > > > > > Also consider that running kernel is often not the same > > > > > thing as installed in /usr/include > > > > > vmlinux and /usr/include are different packages. > > > > > > > > In this case, it's a constant introduced in the kernel in the current > > > > (5.4) cycle; so currently, you can't compile libbpf with > > > > kernel-headers-5.3. And we're discussing how to handle this in a > > > > backwards compatible way in libbpf... > > > > > > you simply don't. > > > It's not a problem to begin with. > > > > hum, that's possible case for distro users.. older kernel, newer libbpf > > yes. older vmlinux and newer installed libbpf.so > or any version of libbpf.a that is statically linked into apps > is something that libbpf code has to support. > The server can be rebooted into older than libbpf kernel and > into newer than libbpf kernel. libbpf has to recognize all these > combinations and work appropriately. > That's what backward and forward compatibility is. > That's what makes libbpf so difficult to test, develop and code review. > What that particular server has in /usr/include is irrelevant. sure, anyway we can't compile following: tredaell@aldebaran ~ $ echo "#include <bpf/xsk.h>" | gcc -x c - In file included from <stdin>:1: /usr/include/bpf/xsk.h: In function ‘xsk_ring_prod__needs_wakeup’: /usr/include/bpf/xsk.h:82:21: error: ‘XDP_RING_NEED_WAKEUP’ undeclared (first use in this function) 82 | return *r->flags & XDP_RING_NEED_WAKEUP; ... XDP_RING_NEED_WAKEUP is defined in kernel v5.4-rc1 (77cd0d7b3f257fd0e3096b4fdcff1a7d38e99e10). XSK_UNALIGNED_BUF_ADDR_MASK and XSK_UNALIGNED_BUF_OFFSET_SHIFT are defined in kernel v5.4-rc1 (c05cd3645814724bdeb32a2b4d953b12bdea5f8c). with: kernel-headers-5.3.6-300.fc31.x86_64 libbpf-0.0.5-1.fc31.x86_64 if you're saying this is not supported, I guess we could be postponing libbpf rpm releases until we have the related fedora kernel released or how about inluding uapi headers in libbpf-devel.. but that might actualy cause more confusion jirka
