bsc_fd: Add a build option to be able to debug fd list corruption

bsc_register_fd on an already registered fd can corrupt the list
in a heavy way and make the select end in an infinite loop, this
code will workaround the issue and provide a way to set a breakpoint
at the right position in the code.

2 files changed, 23 insertions, 0 deletions

diff --git a/configure.in b/configure.in
index c3e00610..1684aaa3 100644
--- a/configure.in
+++ b/configure.in
@@ -77,6 +77,17 @@ then
 	AC_DEFINE([PANIC_INFLOOP],[1],[Use infinite loop on panic rather than fprintf/abort])
 fi
 
+AC_ARG_ENABLE(bsc_fd_check,
+	[AS_HELP_STRING(
+		[--enable-bsc-fd-check],
+		[Instrument bsc_register_fd to check that the fd is registered]
+	)],
+	[fd_check=1], [fd_check=0])
+if test "x$fd_check" = "x1"
+then
+	AC_DEFINE([BSC_FD_CHECK],[1],[Instrument the bsc_register_fd])
+fi
+
 
 AC_OUTPUT(
 	libosmocore.pc
diff --git a/src/select.c b/src/select.c
index 2f6afa7f..f52b0a0c 100644
--- a/src/select.c
+++ b/src/select.c
@@ -19,6 +19,8 @@
  */
 
 #include <fcntl.h>
+#include <stdio.h>
+
 #include <osmocore/select.h>
 #include <osmocore/linuxlist.h>
 #include <osmocore/timer.h>
@@ -48,6 +50,16 @@ int bsc_register_fd(struct bsc_fd *fd)
 	if (fd->fd > maxfd)
 		maxfd = fd->fd;
 
+#ifdef BSC_FD_CHECK
+	struct bsc_fd *entry;
+	llist_for_each_entry(entry, &bsc_fds, list) {
+		if (entry == fd) {
+			fprintf(stderr, "Adding a bsc_fd that is already in the list.\n");
+			return 0;
+		}
+	}
+#endif
+
 	llist_add_tail(&fd->list, &bsc_fds);
 
 	return 0;