[linux] Fail at link time if building slirp.linux without libslirp

The iPXE build system is constructed for a standalone codebase with no
external dependencies, and does not have any equivalent of the
standard userspace ./configure script.  We currently check for the
ability to include slirp/libslirp.h and conditionalise portions of
linux_api.c on its presence.  The actual slirp driver code is built
unconditionally, as with all iPXE drivers.

This currently leads to a silent runtime failure if attempting to use
slirp.linux built on a system that was missing slirp/libslirp.h.

Convert this to a link-time failure by deliberately omitting the
relevant symbols from linux_api.c when slirp/libslirp.h is not
present.  This allows other builds (e.g. tap.linux or tests.linux) to
succeed: the link-time failure will occur only if the slirp driver is
included within the build target.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

diff --git a/src/interface/linux/linux_api.c b/src/interface/linux/linux_api.c
index d1f969aa7195f3d65fb0cc305cb4a112826af2af..21024ede1b42ab3129ab5780ca710e49eb704aae 100644 (file)
--- a/src/interface/linux/linux_api.c
+++ b/src/interface/linux/linux_api.c
@@ -486,35 +486,6 @@ linux_slirp_pollfds_poll ( struct Slirp *slirp, int select_error,
        slirp_pollfds_poll ( slirp, select_error, get_revents, opaque );
 }
 
-#else /* HAVE_LIBSLIRP */
-
-struct Slirp * __asmcall
-linux_slirp_new ( const struct slirp_config *config,
-                 const struct slirp_callbacks *callbacks, void *opaque ) {
-       return NULL;
-}
-
-void __asmcall linux_slirp_cleanup ( struct Slirp *slirp ) {
-}
-
-void __asmcall linux_slirp_input ( struct Slirp *slirp, const uint8_t *pkt,
-                                  int pkt_len ) {
-}
-
-void __asmcall
-linux_slirp_pollfds_fill ( struct Slirp *slirp, uint32_t *timeout,
-                          int ( __asmcall * add_poll ) ( int fd, int events,
-                                                         void *opaque ),
-                          void *opaque ) {
-}
-
-void __asmcall
-linux_slirp_pollfds_poll ( struct Slirp *slirp, int select_error,
-                          int ( __asmcall * get_revents ) ( int idx,
-                                                            void *opaque ),
-                          void *opaque ) {
-}
-
 #endif /* HAVE_LIBSLIRP */
 
 /******************************************************************************
@@ -544,8 +515,11 @@ PROVIDE_IPXE_SYM ( linux_socket );
 PROVIDE_IPXE_SYM ( linux_bind );
 PROVIDE_IPXE_SYM ( linux_sendto );
 PROVIDE_IPXE_SYM ( linux_strerror );
+
+#ifdef HAVE_LIBSLIRP
 PROVIDE_IPXE_SYM ( linux_slirp_new );
 PROVIDE_IPXE_SYM ( linux_slirp_cleanup );
 PROVIDE_IPXE_SYM ( linux_slirp_input );
 PROVIDE_IPXE_SYM ( linux_slirp_pollfds_fill );
 PROVIDE_IPXE_SYM ( linux_slirp_pollfds_poll );
+#endif /* HAVE_LIBSLIRP */