selftests/xsk: do not close unused file descriptors

Do not close descriptors that have never been used. File descriptor
fields that are not in use are erroneously marked with the number 0,
which is a valid fd. Mark unused fds with -1 instead and do not close
these when deleting the socket.
Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
Acked-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Link: https://lore.kernel.org/r/20230111093526.11682-3-magnus.karlsson@gmail.comSigned-off-by: Alexei Starovoitov <ast@kernel.org>

tools/testing/selftests/bpf/xsk.c

@@ -35,6 +35,8 @@
 #include "xsk.h"
 #include "bpf_util.h"
 
+#define FD_NOT_USED (-1)
+
 #ifndef SOL_XDP
  #define SOL_XDP 283
 #endif
@@ -583,6 +585,9 @@ static void xsk_delete_bpf_maps(struct xsk_socket *xsk)
 {
 	struct xsk_ctx *ctx = xsk->ctx;
 
+	if (ctx->xsks_map_fd == FD_NOT_USED)
+		return;
+
 	bpf_map_delete_elem(ctx->xsks_map_fd, &ctx->queue_id);
 	close(ctx->xsks_map_fd);
 }
@@ -941,6 +946,9 @@ static struct xsk_ctx *xsk_create_ctx(struct xsk_socket *xsk,
 	ctx->umem = umem;
 	ctx->queue_id = queue_id;
 	bpf_strlcpy(ctx->ifname, ifname, IFNAMSIZ);
+	ctx->prog_fd = FD_NOT_USED;
+	ctx->link_fd = FD_NOT_USED;
+	ctx->xsks_map_fd = FD_NOT_USED;
 
 	ctx->fill = fill;
 	ctx->comp = comp;
@@ -1221,8 +1229,9 @@ void xsk_socket__delete(struct xsk_socket *xsk)
 
 	if (ctx->refcount == 1) {
 		xsk_delete_bpf_maps(xsk);
+		if (ctx->prog_fd != FD_NOT_USED)
 			close(ctx->prog_fd);
-		if (ctx->has_bpf_link)
+		if (ctx->has_bpf_link && ctx->link_fd != FD_NOT_USED)
 			close(ctx->link_fd);
 	}