bpf, xdp: allow to pass flags to dev_change_xdp_fd

Add an IFLA_XDP_FLAGS attribute that can be passed for setting up
XDP along with IFLA_XDP_FD, which eventually allows user space to
implement typical add/replace/delete logic for programs. Right now,
calling into dev_change_xdp_fd() will always replace previous programs.

When passed XDP_FLAGS_UPDATE_IF_NOEXIST, we can handle this more
graceful when requested by returning -EBUSY in case we try to
attach a new program, but we find that another one is already
attached. This will be used by upcoming front-end for iproute2 as
well.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 18 insertions, 2 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index 048b46b7c92a..bffb5253e778 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6692,26 +6692,42 @@ EXPORT_SYMBOL(dev_change_proto_down);
  *      dev_change_xdp_fd - set or clear a bpf program for a device rx path
  *      @dev: device
  *      @fd: new program fd or negative value to clear
+ *      @flags: xdp-related flags
  *
  *      Set or clear a bpf program for a device
  */
-int dev_change_xdp_fd(struct net_device *dev, int fd)
+int dev_change_xdp_fd(struct net_device *dev, int fd, u32 flags)
 {
         const struct net_device_ops *ops = dev->netdev_ops;
         struct bpf_prog *prog = NULL;
-        struct netdev_xdp xdp = {};
+        struct netdev_xdp xdp;
         int err;
 
+        ASSERT_RTNL();
+
         if (!ops->ndo_xdp)
                 return -EOPNOTSUPP;
         if (fd >= 0) {
+                if (flags & XDP_FLAGS_UPDATE_IF_NOEXIST) {
+                        memset(&xdp, 0, sizeof(xdp));
+                        xdp.command = XDP_QUERY_PROG;
+
+                        err = ops->ndo_xdp(dev, &xdp);
+                        if (err < 0)
+                                return err;
+                        if (xdp.prog_attached)
+                                return -EBUSY;
+                }
+
                 prog = bpf_prog_get_type(fd, BPF_PROG_TYPE_XDP);
                 if (IS_ERR(prog))
                         return PTR_ERR(prog);
         }
 
+        memset(&xdp, 0, sizeof(xdp));
         xdp.command = XDP_SETUP_PROG;
         xdp.prog = prog;
+
         err = ops->ndo_xdp(dev, &xdp);
         if (err < 0 && prog)
                 bpf_prog_put(prog);