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libbb: make rtc_xopen try harder on EBUSY

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function                                             old     new   delta
rtc_xopen                                             77     139     +62

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2014-05-02 09:05:03 +02:00
parent fe33683c8b
commit 528808fa7b
1 changed files with 42 additions and 10 deletions
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52
libbb/rtc.c
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@ -33,23 +33,55 @@ int FAST_FUNC rtc_adjtime_is_utc(void)
return utc; 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 FAST_FUNC rtc_xopen(const char **default_rtc, int flags)
{ {
int rtc; int rtc;
const char *name =
"/dev/rtc""\0"
"/dev/rtc0""\0"
"/dev/misc/rtc""\0";
if (!*default_rtc) { if (!*default_rtc)
*default_rtc = "/dev/rtc"; goto try_name;
rtc = open(*default_rtc, flags); name = ""; /*else: we have rtc name, don't try other names */
for (;;) {
rtc = open_loop_on_busy(*default_rtc, flags);
if (rtc >= 0) if (rtc >= 0)
return rtc; return rtc;
*default_rtc = "/dev/rtc0"; name += strlen(name) + 1;
rtc = open(*default_rtc, flags); if (!name[0])
if (rtc >= 0) return xopen(*default_rtc, flags);
return rtc; try_name:
*default_rtc = "/dev/misc/rtc"; *default_rtc = name;
} }
return xopen(*default_rtc, flags);
} }
void FAST_FUNC rtc_read_tm(struct tm *ptm, int fd) void FAST_FUNC rtc_read_tm(struct tm *ptm, int fd)