uptime: add -s support

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 24 insertions, 6 deletions

diff --git a/procps/uptime.c b/procps/uptime.c
index b0ee8391b..3262f41b4 100644
--- a/procps/uptime.c
+++ b/procps/uptime.c
@@ -45,7 +45,6 @@
 # include <sys/sysinfo.h>
 #endif
 
-
 #ifndef FSHIFT
 # define FSHIFT 16              /* nr of bits of precision */
 #endif
@@ -53,29 +52,48 @@
 #define LOAD_INT(x)  (unsigned)((x) >> FSHIFT)
 #define LOAD_FRAC(x) LOAD_INT(((x) & (FIXED_1 - 1)) * 100)
 
-
 int uptime_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int uptime_main(int argc UNUSED_PARAM, char **argv UNUSED_PARAM)
 {
         unsigned updays, uphours, upminutes;
+        unsigned opts;
         struct sysinfo info;
         struct tm *current_time;
         time_t current_secs;
 
+        opts = getopt32(argv, "s");
+
         time(&current_secs);
+        sysinfo(&info);
+
+        if (opts) // -s
+                current_secs -= info.uptime;
+
         current_time = localtime(&current_secs);
 
-        sysinfo(&info);
+        if (opts) { // -s
+                printf("%04u-%02u-%02u %02u:%02u:%02u\n",
+                        current_time->tm_year + 1900, current_time->tm_mon + 1, current_time->tm_mday,
+                        current_time->tm_hour, current_time->tm_min, current_time->tm_sec
+                );
+                /* The above way of calculating boot time is wobbly,
+                 * info.uptime has only 1 second precision, which makes
+                 * "uptime -s" wander +- one second.
+                 * /proc/uptime may be better, it has 0.01s precision.
+                 */
+                return EXIT_SUCCESS;
+        }
 
         printf(" %02u:%02u:%02u up ",
-                        current_time->tm_hour, current_time->tm_min, current_time->tm_sec);
+                        current_time->tm_hour, current_time->tm_min, current_time->tm_sec
+        );
         updays = (unsigned) info.uptime / (unsigned)(60*60*24);
-        if (updays)
+        if (updays != 0)
                 printf("%u day%s, ", updays, (updays != 1) ? "s" : "");
         upminutes = (unsigned) info.uptime / (unsigned)60;
         uphours = (upminutes / (unsigned)60) % (unsigned)24;
         upminutes %= 60;
-        if (uphours)
+        if (uphours != 0)
                 printf("%2u:%02u", uphours, upminutes);
         else
                 printf("%u min", upminutes);