Hi,

> I wonder if this can be done as helper for TAP/bridge.
>
Well, it does already, libvirt may create TAP device and pass it in command
line or using getfd qmp command.

E.g it's the qemu to launch those helper with set-uid.
>
Then libvirt won't even need to care about that?

Yea, we may think about this routine in the future as a fallback.

Do we need to test whether the bpf can do mmap() here?
>
I'm not sure that it's required.

On Fri, Aug 20, 2021 at 6:41 AM Jason Wang <jasowang@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?
>
>
> > 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 <andrew@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 <andrew@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
>
>