[RFC PATCH Mach] Add a mach host operation which returns elapsed time since bootup

[Zhaoming Luo]

The precision of this implmentation is 10ms. Not sure how to do with the
possible data race.

Signed-off-by: Zhaoming Luo <zhmingluo@163.com>
---
 include/mach/mach_host.defs |  7 +++++++
 kern/mach_clock.c           | 20 ++++++++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/include/mach/mach_host.defs b/include/mach/mach_host.defs
index 8fd9d6b3..67f72cda 100644
--- a/include/mach/mach_host.defs
+++ b/include/mach/mach_host.defs
@@ -386,3 +386,10 @@ routine    host_adjust_time64(
 routine        host_get_kernel_version(
                host            : host_t;
        out     kernel_version  : new_kernel_version_t);
+
+/*
+ *     Get the elapsed time on this host.
+ */
+routine        host_get_elapsed_time(
+               host            : host_t;
+       out     elapsed_time    : time_value_t);
diff --git a/kern/mach_clock.c b/kern/mach_clock.c
index 4b953650..a1e45802 100644
--- a/kern/mach_clock.c
+++ b/kern/mach_clock.c
@@ -571,6 +571,26 @@ host_adjust_time64(
        return (KERN_SUCCESS);
 }
 
+/*
+ * Read the elapsed time since bootup.
+ */
+kern_return_t
+host_get_elapsed_time(const host_t host, time_value_t *elapsed_time)
+{
+       unsigned long read_elapsed_ticks;
+       int64_t elapsed_usec;
+
+       if (host == HOST_NULL)
+               return (KERN_INVALID_HOST);
+
+       read_elapsed_ticks = elapsed_ticks;
+       elapsed_usec = read_elapsed_ticks * tick;
+       elapsed_time->seconds = elapsed_usec / MICROSECONDS_IN_ONE_SECOND;
+       elapsed_time->microseconds = elapsed_usec % MICROSECONDS_IN_ONE_SECOND;
+
+       return (KERN_SUCCESS);
+}
+
 void mapable_time_init(void)
 {
        if (kmem_alloc_wired(kernel_map, (vm_offset_t *) &mtime, PAGE_SIZE)
-- 
2.45.2