1 files changed, 48 insertions, 0 deletions

diff --git a/libbb/poll_with_signals.c b/libbb/poll_with_signals.c
new file mode 100644
index 000000000..d3c005418
--- /dev/null
+++ b/libbb/poll_with_signals.c
@@ -0,0 +1,48 @@
+/* vi: set sw=4 ts=4: */
+/*
+ * Utility routines.
+ *
+ * Copyright (C) 2025 Denys Vlasenko <vda.linux@googlemail.com>
+ *
+ * Licensed under GPLv2, see file LICENSE in this source tree.
+ */
+//kbuild:lib-$(CONFIG_PLATFORM_POSIX) += poll_with_signals.o
+
+#include "libbb.h"
+
+/* Shells, for example, need their line input and "read" builtin
+ * to be interruptible, and the naive handling of it a-la:
+ *      if (bb_got_signal) {
+ *              errno = EINTR;
+ *              return -1;
+ *      }
+ *      poll(pfd, 1, -1); // signal here would set EINTR
+ * is racy.
+ * This is a bit heavy-handed, but safe wrt races:
+ */
+int FAST_FUNC check_got_signal_and_poll(struct pollfd pfd[1], int timeout)
+{
+        int n;
+        struct timespec tv;
+        sigset_t orig_mask;
+
+        if (bb_got_signal) /* optimization */
+                goto eintr;
+
+        if (timeout >= 0) {
+                tv.tv_sec = timeout / 1000;
+                tv.tv_nsec = (timeout % 1000) * 1000000;
+        }
+        /* test bb_got_signal, then poll(), atomically wrt signals */
+        sigfillset(&orig_mask);
+        sigprocmask2(SIG_BLOCK, &orig_mask);
+        if (bb_got_signal) {
+                sigprocmask2(SIG_SETMASK, &orig_mask);
+ eintr:
+                errno = EINTR; /* inform the caller that we got a signal */
+                return -1;
+        }
+        n = ppoll(pfd, 1, timeout >= 0 ? &tv : NULL, &orig_mask);
+        sigprocmask2(SIG_SETMASK, &orig_mask);
+        return n;
+}