On Thu, Mar 11, 2021 at 7:42 AM Maciej Fijalkowski
<maciej.fijalkowski@xxxxxxxxx> wrote:
>
> Currently, if there are multiple xdpsock instances running on a single
> interface and in case one of the instances is terminated, the rest of
> them are left in an inoperable state due to the fact of unloaded XDP
> prog from interface.
>
> Consider the scenario below:
>
> // load xdp prog and xskmap and add entry to xskmap at idx 10
> $ sudo ./xdpsock -i ens801f0 -t -q 10
>
> // add entry to xskmap at idx 11
> $ sudo ./xdpsock -i ens801f0 -t -q 11
>
> terminate one of the processes and another one is unable to work due to
> the fact that the XDP prog was unloaded from interface.
>
> To address that, step away from setting bpf prog in favour of bpf_link.
> This means that refcounting of BPF resources will be done automatically
> by bpf_link itself.
>
> When setting up BPF resources during xsk socket creation, check whether
> bpf_link for a given ifindex already exists via set of calls to
> bpf_link_get_next_id -> bpf_link_get_fd_by_id -> bpf_obj_get_info_by_fd
> and comparing the ifindexes from bpf_link and xsk socket.
>
> If there's no bpf_link yet, create one for a given XDP prog. If bpf_link
> is already at a given ifindex and underlying program is not AF-XDP one,
> bail out or update the bpf_link's prog given the presence of
> XDP_FLAGS_UPDATE_IF_NOEXIST.
>
> If there's netlink-based XDP prog running on a interface, bail out and
> ask user to do removal by himself.
>
> Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@xxxxxxxxx>
> ---
> tools/lib/bpf/xsk.c | 139 ++++++++++++++++++++++++++++++++++++++------
> 1 file changed, 120 insertions(+), 19 deletions(-)
>
[...]
> +static int xsk_link_lookup(struct xsk_ctx *ctx, __u32 *prog_id)
> +{
> + struct bpf_link_info link_info;
> + __u32 link_len;
> + __u32 id = 0;
> + int err;
> + int fd;
> +
> + while (true) {
> + err = bpf_link_get_next_id(id, &id);
> + if (err) {
> + if (errno == ENOENT) {
> + err = 0;
> + break;
> + }
> + pr_warn("can't get next link: %s\n", strerror(errno));
> + break;
> + }
> +
> + fd = bpf_link_get_fd_by_id(id);
> + if (fd < 0) {
> + if (errno == ENOENT)
> + continue;
> + pr_warn("can't get link by id (%u): %s\n", id, strerror(errno));
> + err = -errno;
> + break;
> + }
> +
> + link_len = sizeof(struct bpf_link_info);
> + memset(&link_info, 0, link_len);
> + err = bpf_obj_get_info_by_fd(fd, &link_info, &link_len);
> + if (err) {
> + pr_warn("can't get link info: %s\n", strerror(errno));
> + close(fd);
> + break;
> + }
> + if (link_info.xdp.ifindex == ctx->ifindex) {
how do you know you are looking at XDP bpf_link? link_info.xdp.ifindex
might as well be attach_type for tracing bpf_linke, netns_ino for
netns bpf_link, and so on. Do check link_info.type before check other
per-link type properties.
> + ctx->link_fd = fd;
> + *prog_id = link_info.prog_id;
> + break;
> + }
> + close(fd);
> + }
> +
> + return err;
> +}
> +
> static int __xsk_setup_xdp_prog(struct xsk_socket *_xdp,
> int *xsks_map_fd)
> {
> @@ -675,8 +777,7 @@ static int __xsk_setup_xdp_prog(struct xsk_socket *_xdp,
> __u32 prog_id = 0;
> int err;
>
> - err = bpf_get_link_xdp_id(ctx->ifindex, &prog_id,
> - xsk->config.xdp_flags);
> + err = xsk_link_lookup(ctx, &prog_id);
> if (err)
> return err;
>
> @@ -686,9 +787,12 @@ static int __xsk_setup_xdp_prog(struct xsk_socket *_xdp,
> return err;
>
> err = xsk_load_xdp_prog(xsk);
> - if (err) {
> + if (err)
> goto err_load_xdp_prog;
> - }
> +
> + err = xsk_create_bpf_link(xsk);
> + if (err)
> + goto err_create_bpf_link;
what about the backwards compatibility with kernels that don't yet
support bpf_link?
> } else {
> ctx->prog_fd = bpf_prog_get_fd_by_id(prog_id);
> if (ctx->prog_fd < 0)
[...]
