core: reprint the question every 2 sec in ask_char()

ask_char() now reprints the question every 2sec automatically.

It prefixes its output with '\r' to to bring the cursor to the
beginning of the terminal line, and then print the message, redoing it
every 2sec.

As long as nothing interferes with out output this logic will have no
visible effect as we constantly overprint the visible text with the
exact same text.

However, if something is dumped in the middle, then our question won't
get lost, as we'll ask soon again.

This is useful if the question is asked to a terminal that is also
used to dump some other status messages/logs. For example when
confirmation messages are enabled during the boot
(systemd.confirm_spawn=1), the question can easily be lost if the
kernel logs are also enabled and both use the same console.

Idea suggested by Lennart Poettering.

diff --git a/src/basic/terminal-util.c b/src/basic/terminal-util.c
index 4b04ccc..9a8ef82 100644 (file)
--- a/src/basic/terminal-util.c
+++ b/src/basic/terminal-util.c
@@ -144,12 +144,14 @@ int read_one_char(FILE *f, char *ret, usec_t t, bool *need_nl) {
         return 0;
 }
 
-int ask_char(char *ret, const char *replies, const char *text, ...) {
+#define DEFAULT_ASK_REFRESH_USEC (2*USEC_PER_SEC)
+
+int ask_char(char *ret, const char *replies, const char *fmt, ...) {
         int r;
 
         assert(ret);
         assert(replies);
-        assert(text);
+        assert(fmt);
 
         for (;;) {
                 va_list ap;
@@ -159,8 +161,10 @@ int ask_char(char *ret, const char *replies, const char *text, ...) {
                 if (colors_enabled())
                         fputs(ANSI_HIGHLIGHT, stdout);
 
-                va_start(ap, text);
-                vprintf(text, ap);
+                putchar('\r');
+
+                va_start(ap, fmt);
+                vprintf(fmt, ap);
                 va_end(ap);
 
                 if (colors_enabled())
@@ -168,9 +172,12 @@ int ask_char(char *ret, const char *replies, const char *text, ...) {
 
                 fflush(stdout);
 
-                r = read_one_char(stdin, &c, USEC_INFINITY, &need_nl);
+                r = read_one_char(stdin, &c, DEFAULT_ASK_REFRESH_USEC, &need_nl);
                 if (r < 0) {
 
+                        if (r == -ETIMEDOUT)
+                                continue;
+
                         if (r == -EBADMSG) {
                                 puts("Bad input, please try again.");
                                 continue;