[PATCH 1/1] v2 add StartTimeMonotomic, StartTimeBootTime to per pid in /proc

[Dan Ballard]

starttime in /proc/$PID/stat is inaccurate by "clock tick" granularity.
The process starttime is useful for a variety of things, like figuring
out creation ordering of processes and it is useful to detect PID
reuses in a somewhat reliable way.

The kernel internally stores finer granularity values and this patch
exports them in the easily usable location /prod/$PID/status
as StartTimeMonotonic and StartTimeBootTime.

Signed-off-by: Dan Ballard <dan@xxxxxxxxxxxx>
---
 Documentation/filesystems/proc.txt |    6 +++++-
 fs/proc/array.c                    |    8 ++++++--
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/Documentation/filesystems/proc.txt 
b/Documentation/filesystems/proc.txt
index 22d89aa3..6ed8001 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -158,6 +158,8 @@ read the file /proc/PID/status:
   TracerPid:      0                                            (2.4)
   Uid:    501     501     501     501
   Gid:    100     100     100     100
+  StartTimeMonotonic:     3766799643
+  StartTimeBootTime:      3766799643
   FDSize: 256
   Groups: 100 14 16
   VmPeak:     5004 kB
@@ -202,7 +204,7 @@ asynchronous manner and the vaule may not be very 
precise. To see a precise
 snapshot of a moment, you can see /proc/<pid>/smaps file and scan page 
table.
 It's slow but very precise.

-Table 1-2: Contents of the status files (as of 2.6.30-rc7)
+Table 1-2: Contents of the status files (as of 3.13.0-rc3)

..............................................................................
  Field                       Content
  Name                        filename of the executable
@@ -215,6 +217,8 @@ Table 1-2: Contents of the status files (as of 
2.6.30-rc7)
  TracerPid                   PID of process tracing this process (0 if 
not)
  Uid                         Real, effective, saved set, and  file 
system UIDs
  Gid                         Real, effective, saved set, and  file 
system GIDs
+ StartTimeMonotonic          Start time of process in nsec from 
CLOCK_MONOTONIC
+ StartTimeBootTime           Start time of process in nsec from 
CLOCK_BOOTTIME
  FDSize                      number of file descriptor slots currently 
allocated
  Groups                      supplementary group list
  VmPeak                      peak virtual memory size
diff --git a/fs/proc/array.c b/fs/proc/array.c
index 1bd2077..34f4761 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -188,7 +188,9 @@ static inline void task_state(struct seq_file *m, 
struct pid_namespace *ns,
                "PPid:\t%d\n"
                "TracerPid:\t%d\n"
                "Uid:\t%d\t%d\t%d\t%d\n"
-               "Gid:\t%d\t%d\t%d\t%d\n",
+               "Gid:\t%d\t%d\t%d\t%d\n"
+               "StartTimeMonotonic:\t%lld\n"
+               "StartTimeBootTime:\t%lld\n",
                get_task_state(p),
                task_tgid_nr_ns(p, ns),
                task_numa_group_id(p),
@@ -201,7 +203,9 @@ static inline void task_state(struct seq_file *m, 
struct pid_namespace *ns,
                from_kgid_munged(user_ns, cred->gid),
                from_kgid_munged(user_ns, cred->egid),
                from_kgid_munged(user_ns, cred->sgid),
-               from_kgid_munged(user_ns, cred->fsgid));
+               from_kgid_munged(user_ns, cred->fsgid),
+               timespec_to_ns(&p->start_time),
+               timespec_to_ns(&p->real_start_time));

        task_lock(p);
        if (p->files)
--
1.7.10.4
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