Hi, > I think it's for back-compatibility. > > E.g current codes works without mmap(), and user will surprise that it > wont' work after upgrading their qemu. > Well, the current code would require additional capabilities with "kernel.unprivileged_bpf_disabled=1", which may be possible on RedHat systems. Technically we may have mmap test which will show that mmap for BPF_MAP_TYPE_ARRAY works, but on the target system, we will know it only in runtime. If I'm not mistaken, mmap for BPF_MAP_TYPE_ARRAY was added before kernel 5.4 and our bpf program requires kernel 5.8+. So, there are no reasons to add bpf() update map as a fallback for mmap().
On Wed, Sep 1, 2021 at 9:42 AM Jason Wang <jasow...@redhat.com> wrote: > > 在 2021/8/31 上午1:07, Yuri Benditovich 写道: > > On Fri, Aug 20, 2021 at 6:41 AM Jason Wang <jasow...@redhat.com> wrote: > >> > >> 在 2021/7/13 下午11:37, Andrew Melnychenko 写道: > >>> Helper program. Loads eBPF RSS program and maps and passes them > through unix socket. > >>> Libvirt may launch this helper and pass eBPF fds to qemu virtio-net. > >> > >> I wonder if this can be done as helper for TAP/bridge. > >> > >> E.g it's the qemu to launch those helper with set-uid. > >> > >> Then libvirt won't even need to care about that? > >> > > There are pros and cons for such a solution with set-uid. > > From my point of view one of the cons is that set-uid is efficient > > only at install time so the coexistence of different qemu builds (and > > different helpers for each one) is kind of problematic. > > With the current solution this does not present any problem: the > > developer can have several different builds, each one automatically > > has its own helper and there is no conflict between these builds and > > between these builds and installed qemu package. Changing the > > 'emulator' in the libvirt profile automatically brings the proper > > helper to work. > > > I'm not sure I get you here. We can still have default/sample helper to > make sure it works for different builds. > > If we can avoid the involvement of libvirt, that would be better. > > Thanks > > > > > >>> Also, libbpf dependency now exclusively for Linux. > >>> Libbpf is used for eBPF RSS steering, which is supported only by Linux > TAP. > >>> There is no reason yet to build eBPF loader and helper for non Linux > systems, > >>> even if libbpf is present. > >>> > >>> Signed-off-by: Andrew Melnychenko <and...@daynix.com> > >>> --- > >>> ebpf/qemu-ebpf-rss-helper.c | 130 > ++++++++++++++++++++++++++++++++++++ > >>> meson.build | 37 ++++++---- > >>> 2 files changed, 154 insertions(+), 13 deletions(-) > >>> create mode 100644 ebpf/qemu-ebpf-rss-helper.c > >>> > >>> diff --git a/ebpf/qemu-ebpf-rss-helper.c b/ebpf/qemu-ebpf-rss-helper.c > >>> new file mode 100644 > >>> index 0000000000..fe68758f57 > >>> --- /dev/null > >>> +++ b/ebpf/qemu-ebpf-rss-helper.c > >>> @@ -0,0 +1,130 @@ > >>> +/* > >>> + * eBPF RSS Helper > >>> + * > >>> + * Developed by Daynix Computing LTD (http://www.daynix.com) > >>> + * > >>> + * Authors: > >>> + * Andrew Melnychenko <and...@daynix.com> > >>> + * > >>> + * This work is licensed under the terms of the GNU GPL, version 2. > See > >>> + * the COPYING file in the top-level directory. > >>> + * > >>> + * Description: This is helper program for libvirtd. > >>> + * It loads eBPF RSS program and passes fds through unix > socket. > >>> + * Built by meson, target - 'qemu-ebpf-rss-helper'. > >>> + */ > >>> + > >>> +#include <stdio.h> > >>> +#include <stdint.h> > >>> +#include <stdlib.h> > >>> +#include <stdbool.h> > >>> +#include <getopt.h> > >>> +#include <memory.h> > >>> +#include <errno.h> > >>> +#include <sys/socket.h> > >>> + > >>> +#include "ebpf_rss.h" > >>> + > >>> +#include "qemu-helper-stamp.h" > >>> + > >>> +void QEMU_HELPER_STAMP(void) {} > >>> + > >>> +static int send_fds(int socket, int *fds, int n) > >>> +{ > >>> + struct msghdr msg = {}; > >>> + struct cmsghdr *cmsg = NULL; > >>> + char buf[CMSG_SPACE(n * sizeof(int))]; > >>> + char dummy_buffer = 0; > >>> + struct iovec io = { .iov_base = &dummy_buffer, > >>> + .iov_len = sizeof(dummy_buffer) }; > >>> + > >>> + memset(buf, 0, sizeof(buf)); > >>> + > >>> + msg.msg_iov = &io; > >>> + msg.msg_iovlen = 1; > >>> + msg.msg_control = buf; > >>> + msg.msg_controllen = sizeof(buf); > >>> + > >>> + cmsg = CMSG_FIRSTHDR(&msg); > >>> + cmsg->cmsg_level = SOL_SOCKET; > >>> + cmsg->cmsg_type = SCM_RIGHTS; > >>> + cmsg->cmsg_len = CMSG_LEN(n * sizeof(int)); > >>> + > >>> + memcpy(CMSG_DATA(cmsg), fds, n * sizeof(int)); > >>> + > >>> + return sendmsg(socket, &msg, 0); > >>> +} > >>> + > >>> +static void print_help_and_exit(const char *prog, int exitcode) > >>> +{ > >>> + fprintf(stderr, "%s - load eBPF RSS program for qemu and pass > eBPF fds" > >>> + " through unix socket.\n", prog); > >>> + fprintf(stderr, "\t--fd <num>, -f <num> - unix socket file > descriptor" > >>> + " used to pass eBPF fds.\n"); > >>> + fprintf(stderr, "\t--help, -h - this help.\n"); > >>> + exit(exitcode); > >>> +} > >>> + > >>> +int main(int argc, char **argv) > >>> +{ > >>> + char *fd_string = NULL; > >>> + int unix_fd = 0; > >>> + struct EBPFRSSContext ctx = {}; > >>> + int fds[EBPF_RSS_MAX_FDS] = {}; > >>> + int ret = -1; > >>> + > >>> + for (;;) { > >>> + int c; > >>> + static struct option long_options[] = { > >>> + {"help", no_argument, 0, 'h'}, > >>> + {"fd", required_argument, 0, 'f'}, > >>> + {0, 0, 0, 0} > >>> + }; > >>> + c = getopt_long(argc, argv, "hf:", > >>> + long_options, NULL); > >>> + > >>> + if (c == -1) { > >>> + break; > >>> + } > >>> + > >>> + switch (c) { > >>> + case 'f': > >>> + fd_string = optarg; > >>> + break; > >>> + case 'h': > >>> + default: > >>> + print_help_and_exit(argv[0], > >>> + c == 'h' ? EXIT_SUCCESS : EXIT_FAILURE); > >>> + } > >>> + } > >>> + > >>> + if (!fd_string) { > >>> + fprintf(stderr, "Unix file descriptor not present.\n"); > >>> + print_help_and_exit(argv[0], EXIT_FAILURE); > >>> + } > >>> + > >>> + unix_fd = atoi(fd_string); > >>> + > >>> + if (!unix_fd) { > >>> + fprintf(stderr, "Unix file descriptor is invalid.\n"); > >>> + return EXIT_FAILURE; > >>> + } > >>> + > >>> + ebpf_rss_init(&ctx); > >>> + if (!ebpf_rss_load(&ctx)) { > >>> + fprintf(stderr, "Can't load ebpf.\n"); > >>> + return EXIT_FAILURE; > >>> + } > >>> + fds[0] = ctx.program_fd; > >>> + fds[1] = ctx.map_configuration; > >>> + > >>> + ret = send_fds(unix_fd, fds, EBPF_RSS_MAX_FDS); > >>> + if (ret < 0) { > >>> + fprintf(stderr, "Issue while sending fds: %s.\n", > strerror(errno)); > >>> + } > >>> + > >>> + ebpf_rss_unload(&ctx); > >>> + > >>> + return ret < 0 ? EXIT_FAILURE : EXIT_SUCCESS; > >>> +} > >>> + > >>> diff --git a/meson.build b/meson.build > >>> index 257e51d91b..913aa1fee5 100644 > >>> --- a/meson.build > >>> +++ b/meson.build > >>> @@ -1033,19 +1033,22 @@ if not get_option('fuse_lseek').disabled() > >>> endif > >>> > >>> # libbpf > >>> -libbpf = dependency('libbpf', required: get_option('bpf'), method: > 'pkg-config') > >>> -if libbpf.found() and not cc.links(''' > >>> - #include <bpf/libbpf.h> > >>> - int main(void) > >>> - { > >>> - bpf_object__destroy_skeleton(NULL); > >>> - return 0; > >>> - }''', dependencies: libbpf) > >>> - libbpf = not_found > >>> - if get_option('bpf').enabled() > >>> - error('libbpf skeleton test failed') > >>> - else > >>> - warning('libbpf skeleton test failed, disabling') > >>> +libbpf = not_found > >>> +if targetos == 'linux' > >>> + libbpf = dependency('libbpf', required: get_option('bpf'), method: > 'pkg-config') > >>> + if libbpf.found() and not cc.links(''' > >>> + #include <bpf/libbpf.h> > >>> + int main(void) > >>> + { > >>> + bpf_object__destroy_skeleton(NULL); > >> > >> Do we need to test whether the bpf can do mmap() here? > >> > >> Thanks > >> > >> > >>> + return 0; > >>> + }''', dependencies: libbpf) > >>> + libbpf = not_found > >>> + if get_option('bpf').enabled() > >>> + error('libbpf skeleton test failed') > >>> + else > >>> + warning('libbpf skeleton test failed, disabling') > >>> + endif > >>> endif > >>> endif > >>> > >>> @@ -2423,6 +2426,14 @@ if have_tools > >>> dependencies: [authz, crypto, io, qom, qemuutil, > >>> libcap_ng, mpathpersist], > >>> install: true) > >>> + > >>> + if libbpf.found() > >>> + executable('qemu-ebpf-rss-helper', files( > >>> + 'ebpf/qemu-ebpf-rss-helper.c', 'ebpf/ebpf_rss.c'), > >>> + dependencies: [qemuutil, libbpf, glib], > >>> + install: true, > >>> + install_dir: get_option('libexecdir')) > >>> + endif > >>> endif > >>> > >>> if 'CONFIG_IVSHMEM' in config_host > >
