From 528808fa7b0778931fb624e95c38cf8cbc2fff90 Mon Sep 17 00:00:00 2001
From: Denys Vlasenko <vda.linux@googlemail.com>
Date: Fri, 2 May 2014 09:05:03 +0200
Subject: libbb: make rtc_xopen try harder on EBUSY
function old new delta
rtc_xopen 77 139 +62
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
---
libbb/rtc.c | 52 ++++++++++++++++++++++++++++++++++++++++++----------
1 file changed, 42 insertions(+), 10 deletions(-)
diff --git a/libbb/rtc.c b/libbb/rtc.c
index 97455e86a..f84da09bb 100644
--- a/libbb/rtc.c
+++ b/libbb/rtc.c
@@ -33,23 +33,55 @@ int FAST_FUNC rtc_adjtime_is_utc(void)
return utc;
}
+/* rtc opens are exclusive.
+ * Try to run two "hwclock -w" at the same time to see it.
+ * Users wouldn't expect that to fail merely because /dev/rtc
+ * was momentarily busy, let's try a bit harder on errno == EBUSY.
+ */
+static int open_loop_on_busy(const char *name, int flags)
+{
+ int rtc;
+ /*
+ * Tested with two parallel "hwclock -w" loops.
+ * With try = 10, no failures with 2x1000000 loop iterations.
+ */
+ int try = 1000 / 20;
+ again:
+ errno = 0;
+ rtc = open(name, flags);
+ if (errno == EBUSY) {
+ usleep(20 * 1000);
+ if (--try != 0)
+ goto again;
+ /* EBUSY. Last try, exit on error instead of returning -1 */
+ return xopen(name, flags);
+ }
+ return rtc;
+}
+
+/* Never fails */
int FAST_FUNC rtc_xopen(const char **default_rtc, int flags)
{
int rtc;
+ const char *name =
+ "/dev/rtc""\0"
+ "/dev/rtc0""\0"
+ "/dev/misc/rtc""\0";
- if (!*default_rtc) {
- *default_rtc = "/dev/rtc";
- rtc = open(*default_rtc, flags);
- if (rtc >= 0)
- return rtc;
- *default_rtc = "/dev/rtc0";
- rtc = open(*default_rtc, flags);
+ if (!*default_rtc)
+ goto try_name;
+ name = ""; /*else: we have rtc name, don't try other names */
+
+ for (;;) {
+ rtc = open_loop_on_busy(*default_rtc, flags);
if (rtc >= 0)
return rtc;
- *default_rtc = "/dev/misc/rtc";
+ name += strlen(name) + 1;
+ if (!name[0])
+ return xopen(*default_rtc, flags);
+ try_name:
+ *default_rtc = name;
}
-
- return xopen(*default_rtc, flags);
}
void FAST_FUNC rtc_read_tm(struct tm *ptm, int fd)
--
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