Maciej Fijalkowski <maciej.fijalkowski@xxxxxxxxx> writes:
> 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.
>
> Provide backward compatibility by checking if underlying system is
> bpf_link capable. Do this by looking up/creating bpf_link on loopback
> device. If it failed in any way, stick with netlink-based XDP prog.
> therwise, use bpf_link-based logic.
>
> 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.
>
> For case where resources exist but they are not AF_XDP related, bail out
> and ask user to remove existing prog and then retry.
>
> Lastly, do a bit of refactoring within __xsk_setup_xdp_prog and pull out
> existing code branches based on prog_id value onto separate functions
> that are responsible for resource initialization if prog_id was 0 and
> for lookup existing resources for non-zero prog_id as that implies that
> XDP program is present on the underlying net device. This in turn makes
> it easier to follow, especially the teardown part of both branches.
>
> Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@xxxxxxxxx>
The logic is much improved in this version! A few smallish issues below:
> ---
> tools/lib/bpf/xsk.c | 259 ++++++++++++++++++++++++++++++++++++--------
> 1 file changed, 214 insertions(+), 45 deletions(-)
>
> diff --git a/tools/lib/bpf/xsk.c b/tools/lib/bpf/xsk.c
> index 526fc35c0b23..c75067f0035f 100644
> --- a/tools/lib/bpf/xsk.c
> +++ b/tools/lib/bpf/xsk.c
> @@ -28,6 +28,7 @@
> #include <sys/mman.h>
> #include <sys/socket.h>
> #include <sys/types.h>
> +#include <linux/if_link.h>
>
> #include "bpf.h"
> #include "libbpf.h"
> @@ -70,8 +71,10 @@ struct xsk_ctx {
> int ifindex;
> struct list_head list;
> int prog_fd;
> + int link_fd;
> int xsks_map_fd;
> char ifname[IFNAMSIZ];
> + bool has_bpf_link;
> };
>
> struct xsk_socket {
> @@ -409,7 +412,7 @@ static int xsk_load_xdp_prog(struct xsk_socket *xsk)
> static const int log_buf_size = 16 * 1024;
> struct xsk_ctx *ctx = xsk->ctx;
> char log_buf[log_buf_size];
> - int err, prog_fd;
> + int prog_fd;
>
> /* This is the fallback C-program:
> * SEC("xdp_sock") int xdp_sock_prog(struct xdp_md *ctx)
> @@ -499,14 +502,43 @@ static int xsk_load_xdp_prog(struct xsk_socket *xsk)
> return prog_fd;
> }
>
> - err = bpf_set_link_xdp_fd(xsk->ctx->ifindex, prog_fd,
> - xsk->config.xdp_flags);
> + ctx->prog_fd = prog_fd;
> + return 0;
> +}
> +
> +static int xsk_create_bpf_link(struct xsk_socket *xsk)
> +{
> + /* bpf_link only accepts XDP_FLAGS_MODES, but xsk->config.xdp_flags
> + * might have set XDP_FLAGS_UPDATE_IF_NOEXIST
> + */
> + DECLARE_LIBBPF_OPTS(bpf_link_create_opts, opts,
> + .flags = (xsk->config.xdp_flags & XDP_FLAGS_MODES));
This will silently suppress any new flags as well; that's not a good
idea. Rather mask out the particular flag (UPDATE_IF_NOEXIST) and pass
everything else through so the kernel can reject invalid ones.
> + struct xsk_ctx *ctx = xsk->ctx;
> + __u32 prog_id = 0;
> + int link_fd;
> + int err;
> +
> + err = bpf_get_link_xdp_id(ctx->ifindex, &prog_id, xsk->config.xdp_flags);
> if (err) {
> - close(prog_fd);
> + pr_warn("getting XDP prog id failed\n");
> return err;
> }
>
> - ctx->prog_fd = prog_fd;
> + /* if there's a netlink-based XDP prog loaded on interface, bail out
> + * and ask user to do the removal by himself
> + */
> + if (prog_id) {
> + pr_warn("Netlink-based XDP prog detected, please unload it in order to launch AF_XDP prog\n");
> + return -EINVAL;
> + }
> +
> + link_fd = bpf_link_create(ctx->prog_fd, ctx->ifindex, BPF_XDP, &opts);
> + if (link_fd < 0) {
> + pr_warn("bpf_link_create failed: %s\n", strerror(errno));
> + return link_fd;
> + }
> +
> + ctx->link_fd = link_fd;
> return 0;
> }
>
> @@ -625,7 +657,6 @@ static int xsk_lookup_bpf_maps(struct xsk_socket *xsk)
> close(fd);
> }
>
> - err = 0;
> if (ctx->xsks_map_fd == -1)
> err = -ENOENT;
>
> @@ -642,6 +673,97 @@ static int xsk_set_bpf_maps(struct xsk_socket *xsk)
> &xsk->fd, 0);
> }
>
> +static int xsk_link_lookup(int ifindex, __u32 *prog_id, int *link_fd)
> +{
> + 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.type == BPF_LINK_TYPE_XDP) {
> + if (link_info.xdp.ifindex == ifindex) {
> + *link_fd = fd;
> + if (prog_id)
> + *prog_id = link_info.prog_id;
> + break;
> + }
> + }
> + close(fd);
> + }
> +
> + return err;
> +}
> +
> +static bool xsk_probe_bpf_link(void)
> +{
> + DECLARE_LIBBPF_OPTS(bpf_link_create_opts, opts,
> + .flags = XDP_FLAGS_SKB_MODE);
> + struct bpf_load_program_attr prog_attr;
> + struct bpf_insn insns[2] = {
> + BPF_MOV64_IMM(BPF_REG_0, XDP_PASS),
> + BPF_EXIT_INSN()
> + };
> + int prog_fd, link_fd = -1;
> + int ifindex_lo = 1;
> + bool ret = false;
> + int err;
> +
> + err = xsk_link_lookup(ifindex_lo, NULL, &link_fd);
> + if (err)
> + return ret;
> +
> + if (link_fd >= 0)
> + return true;
> +
> + memset(&prog_attr, 0, sizeof(prog_attr));
> + prog_attr.prog_type = BPF_PROG_TYPE_XDP;
> + prog_attr.insns = insns;
> + prog_attr.insns_cnt = ARRAY_SIZE(insns);
> + prog_attr.license = "GPL";
> +
> + prog_fd = bpf_load_program_xattr(&prog_attr, NULL, 0);
> + if (prog_fd < 0)
> + return ret;
> +
> + link_fd = bpf_link_create(prog_fd, ifindex_lo, BPF_XDP, &opts);
> + if (link_fd >= 0)
> + ret = true;
> +
> + close(prog_fd);
> + close(link_fd);
This potentially calls close() on an invalid link_fd...
> +
> + return ret;
> +}
> +
> static int xsk_create_xsk_struct(int ifindex, struct xsk_socket *xsk)
> {
> char ifname[IFNAMSIZ];
> @@ -663,64 +785,108 @@ static int xsk_create_xsk_struct(int ifindex, struct xsk_socket *xsk)
> ctx->ifname[IFNAMSIZ - 1] = 0;
>
> xsk->ctx = ctx;
> + xsk->ctx->has_bpf_link = xsk_probe_bpf_link();
>
> return 0;
> }
>
> -static int __xsk_setup_xdp_prog(struct xsk_socket *_xdp,
> - int *xsks_map_fd)
> +static int xsk_init_xdp_res(struct xsk_socket *xsk,
> + int *xsks_map_fd)
> {
> - struct xsk_socket *xsk = _xdp;
> struct xsk_ctx *ctx = xsk->ctx;
> - __u32 prog_id = 0;
> int err;
>
> - err = bpf_get_link_xdp_id(ctx->ifindex, &prog_id,
> - xsk->config.xdp_flags);
> + err = xsk_create_bpf_maps(xsk);
> if (err)
> return err;
>
> - if (!prog_id) {
> - err = xsk_create_bpf_maps(xsk);
> - if (err)
> - return err;
> + err = xsk_load_xdp_prog(xsk);
> + if (err)
> + goto err_load_xdp_prog;
>
> - err = xsk_load_xdp_prog(xsk);
> - if (err) {
> - goto err_load_xdp_prog;
> - }
> - } else {
> - ctx->prog_fd = bpf_prog_get_fd_by_id(prog_id);
> - if (ctx->prog_fd < 0)
> - return -errno;
> - err = xsk_lookup_bpf_maps(xsk);
> - if (err) {
> - close(ctx->prog_fd);
> - return err;
> - }
> - }
> + if (ctx->has_bpf_link)
> + err = xsk_create_bpf_link(xsk);
> + else
> + err = bpf_set_link_xdp_fd(xsk->ctx->ifindex, ctx->prog_fd,
> + xsk->config.xdp_flags);
>
> - if (xsk->rx) {
> - err = xsk_set_bpf_maps(xsk);
> - if (err) {
> - if (!prog_id) {
> - goto err_set_bpf_maps;
> - } else {
> - close(ctx->prog_fd);
> - return err;
> - }
> - }
> - }
> - if (xsks_map_fd)
> - *xsks_map_fd = ctx->xsks_map_fd;
> + if (err)
> + goto err_atach_xdp_prog;
s/atach/attach/
-Toke
