| #!/usr/bin/python |
| # Copyright 2012 Google Inc. All Rights Reserved. |
| |
| """Antirollback clock user space support. |
| |
| This daemon serves several purposes: |
| 1. Maintain a file containing the minimum time, and periodically |
| update its value. |
| 2. At startup, write the minimum time to /proc/ar_clock. |
| The kernel will not allow the time to be set substantially |
| earlier than this value (there is a small amount of wiggle |
| room). |
| """ |
| |
| __author__ = 'dgentry@google.com (Denton Gentry)' |
| |
| import os |
| import pwd |
| import sys |
| import tempfile |
| import time |
| import options |
| |
| |
| optspec = """ |
| antirollback [options...] |
| -- |
| i,interval= seconds between updates [28800] |
| p,persist= path to persistent file [/fiber/config/ar_clock] |
| u,user= setuid to this user to run |
| """ |
| |
| |
| # Unit tests can override these. |
| BIRTHDAY = 1349064000.0 # 10/1/2012 |
| BUILD_FILENAME = '/etc/softwaredate' |
| PROC_AR = '/proc/ar_clock' |
| PROC_UPTIME = '/proc/uptime' |
| SLEEP = time.sleep |
| TIMENOW = time.time |
| |
| |
| def GetPersistTime(ar_filename): |
| """Return time stored in ar_filename, or 0.0 if it does not exist.""" |
| try: |
| with open(ar_filename) as f: |
| return float(f.read()) |
| except (IOError, ValueError): |
| return 0.0 |
| |
| |
| def GetBuildDate(build_filename): |
| """Return build_date in floating point seconds since epoch.""" |
| try: |
| with open(build_filename) as f: |
| return float(f.readline()) |
| except (IOError, ValueError): |
| return 0.0 |
| |
| |
| def GetMonotime(): |
| """Return a monotonically increasing count of seconds.""" |
| return float(open(PROC_UPTIME).read().split()[0]) |
| |
| |
| def GetAntirollbackTime(ar_filename): |
| """Return the appropriate antirollback time to use at startup.""" |
| now = max(TIMENOW(), GetPersistTime(ar_filename), |
| GetBuildDate(BUILD_FILENAME), BIRTHDAY) |
| return now |
| |
| |
| def StoreAntirollback(now, ar_filename, kern_f): |
| """Write time to /proc/ar_clock and the persistent file.""" |
| print 'antirollback time now ' + str(now) |
| sys.stdout.flush() |
| kern_f.write(str(now)) |
| kern_f.flush() |
| tmpdir = os.path.dirname(ar_filename) |
| with tempfile.NamedTemporaryFile(mode='w', dir=tmpdir, delete=False) as f: |
| f.write(str(now) + '\n') |
| f.flush() |
| os.fsync(f.fileno()) |
| os.rename(f.name, ar_filename) |
| |
| |
| def LoopIterate(uptime, now, sleeptime, ar_filename, kern_f): |
| SLEEP(sleeptime) |
| new_uptime = GetMonotime() |
| now += (new_uptime - uptime) |
| uptime = new_uptime |
| now = max(now, TIMENOW()) |
| StoreAntirollback(now=now, ar_filename=ar_filename, kern_f=kern_f) |
| return (uptime, now) |
| |
| |
| def main(): |
| o = options.Options(optspec) |
| (opt, _, _) = o.parse(sys.argv[1:]) |
| |
| kern_f = open(PROC_AR, 'w') |
| |
| # Drop privileges |
| if opt.user: |
| pd = pwd.getpwnam(opt.user) |
| os.setuid(pd.pw_uid) |
| |
| uptime = GetMonotime() |
| now = GetAntirollbackTime(opt.persist) |
| |
| StoreAntirollback(now=now, ar_filename=opt.persist, kern_f=kern_f) |
| |
| while True: |
| (uptime, now) = LoopIterate(uptime=uptime, now=now, |
| sleeptime=opt.interval, |
| ar_filename=opt.persist, |
| kern_f=kern_f) |
| |
| |
| if __name__ == '__main__': |
| main() |