[ViewVC] Diff of: cvs/libev/ev.3

Comparing libev/ev.3 (file contents):
Revision 1.57 by root, Sat Dec 22 11:49:17 2007 UTC vs.
Revision 1.59 by root, Tue Dec 25 07:16:53 2007 UTC

 .\}
 .rm #[ #] #H #V #F C
 .\" ========================================================================
 .\"
 .IX Title "EV 1"
-.TH EV 1 "2007-12-22" "perl v5.8.8" "User Contributed Perl Documentation"
+.TH EV 1 "2007-12-25" "perl v5.8.8" "User Contributed Perl Documentation"
 .SH "NAME"
 libev \- a high performance full\-featured event loop written in C
 .SH "SYNOPSIS"
 .IX Header "SYNOPSIS"
 .Vb 1
 \&  #include <ev.h>
 .Ve
-.SH "EXAMPLE PROGRAM"
+.Sh "\s-1EXAMPLE\s0 \s-1PROGRAM\s0"
-.IX Header "EXAMPLE PROGRAM"
+.IX Subsection "EXAMPLE PROGRAM"
 .Vb 1
 \&  #include <ev.h>
 .Ve
 .PP
 .Vb 2
 .PP
 You register interest in certain events by registering so-called \fIevent
 watchers\fR, which are relatively small C structures you initialise with the
 details of the event, and then hand it over to libev by \fIstarting\fR the
 watcher.
-.SH "FEATURES"
+.Sh "\s-1FEATURES\s0"
-.IX Header "FEATURES"
+.IX Subsection "FEATURES"
 Libev supports \f(CW\*(C`select\*(C'\fR, \f(CW\*(C`poll\*(C'\fR, the Linux-specific \f(CW\*(C`epoll\*(C'\fR, the
 BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port mechanisms
 for file descriptor events (\f(CW\*(C`ev_io\*(C'\fR), the Linux \f(CW\*(C`inotify\*(C'\fR interface
 (for \f(CW\*(C`ev_stat\*(C'\fR), relative timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers
 with customised rescheduling (\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals
 (\f(CW\*(C`ev_fork\*(C'\fR).
 .PP
 It also is quite fast (see this
 benchmark comparing it to libevent
 for example).
-.SH "CONVENTIONS"
+.Sh "\s-1CONVENTIONS\s0"
-.IX Header "CONVENTIONS"
+.IX Subsection "CONVENTIONS"
 Libev is very configurable. In this manual the default configuration will
 be described, which supports multiple event loops. For more info about
 various configuration options please have a look at \fB\s-1EMBED\s0\fR section in
 this manual. If libev was configured without support for multiple event
 loops, then all functions taking an initial argument of name \f(CW\*(C`loop\*(C'\fR
 (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) will not have this argument.
-.SH "TIME REPRESENTATION"
+.Sh "\s-1TIME\s0 \s-1REPRESENTATION\s0"
-.IX Header "TIME REPRESENTATION"
+.IX Subsection "TIME REPRESENTATION"
 Libev represents time as a single floating point number, representing the
 (fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere near
 the beginning of 1970, details are complicated, don't ask). This type is
 called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use too. It usually aliases
 to the \f(CW\*(C`double\*(C'\fR type in C, and when you need to do any calculations on
 .el .IP "\f(CWEVBACKEND_SELECT\fR  (value 1, portable select backend)" 4
 .IX Item "EVBACKEND_SELECT  (value 1, portable select backend)"
 This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as
 libev tries to roll its own fd_set with no limits on the number of fds,
 but if that fails, expect a fairly low limit on the number of fds when
-using this backend. It doesn't scale too well (O(highest_fd)), but its usually
+using this backend. It doesn't scale too well (O(highest_fd)), but its
-the fastest backend for a low number of fds.
+usually the fastest backend for a low number of (low\-numbered :) fds.
+.Sp
+To get good performance out of this backend you need a high amount of
+parallelity (most of the file descriptors should be busy). If you are
+writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many
+connections as possible during one iteration. You might also want to have
+a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of
+readyness notifications you get per iteration.
 .ie n .IP """EVBACKEND_POLL""    (value 2, poll backend, available everywhere except on windows)" 4
 .el .IP "\f(CWEVBACKEND_POLL\fR    (value 2, poll backend, available everywhere except on windows)" 4
 .IX Item "EVBACKEND_POLL    (value 2, poll backend, available everywhere except on windows)"
-And this is your standard \fIpoll\fR\|(2) backend. It's more complicated than
+And this is your standard \fIpoll\fR\|(2) backend. It's more complicated
-select, but handles sparse fds better and has no artificial limit on the
+than select, but handles sparse fds better and has no artificial
-number of fds you can use (except it will slow down considerably with a
+limit on the number of fds you can use (except it will slow down
-lot of inactive fds). It scales similarly to select, i.e. O(total_fds).
+considerably with a lot of inactive fds). It scales similarly to select,
+i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for
+performance tips.
 .ie n .IP """EVBACKEND_EPOLL""   (value 4, Linux)" 4
 .el .IP "\f(CWEVBACKEND_EPOLL\fR   (value 4, Linux)" 4
 .IX Item "EVBACKEND_EPOLL   (value 4, Linux)"
 For few fds, this backend is a bit little slower than poll and select,
 but it scales phenomenally better. While poll and select usually scale
 like O(total_fds) where n is the total number of fds (or the highest fd),
 epoll scales either O(1) or O(active_fds). The epoll design has a number
 of shortcomings, such as silently dropping events in some hard-to-detect
 cases and rewiring a syscall per fd change, no fork support and bad
-support for dup:
+support for dup.
 .Sp
 While stopping, setting and starting an I/O watcher in the same iteration
 will result in some caching, there is still a syscall per such incident
 (because the fd could point to a different file description now), so its
 best to avoid that. Also, \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors might not work
 very well if you register events for both fds.
 .Sp
 Please note that epoll sometimes generates spurious notifications, so you
 need to use non-blocking I/O or other means to avoid blocking when no data
 (or space) is available.
+.Sp
+Best performance from this backend is achieved by not unregistering all
+watchers for a file descriptor until it has been closed, if possible, i.e.
+keep at least one watcher active per fd at all times.
+.Sp
+While nominally embeddeble in other event loops, this feature is broken in
+all kernel versions tested so far.
 .ie n .IP """EVBACKEND_KQUEUE""  (value 8, most \s-1BSD\s0 clones)" 4
 .el .IP "\f(CWEVBACKEND_KQUEUE\fR  (value 8, most \s-1BSD\s0 clones)" 4
 .IX Item "EVBACKEND_KQUEUE  (value 8, most BSD clones)"
 Kqueue deserves special mention, as at the time of this writing, it
 was broken on all BSDs except NetBSD (usually it doesn't work reliably
 kernel is more efficient (which says nothing about its actual speed, of
 course). While stopping, setting and starting an I/O watcher does never
 cause an extra syscall as with \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to
 two event changes per incident, support for \f(CW\*(C`fork ()\*(C'\fR is very bad and it
 drops fds silently in similarly hard-to-detect cases.
+.Sp
+This backend usually performs well under most conditions.
+.Sp
+While nominally embeddable in other event loops, this doesn't work
+everywhere, so you might need to test for this. And since it is broken
+almost everywhere, you should only use it when you have a lot of sockets
+(for which it usually works), by embedding it into another event loop
+(e.g. \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR) and using it only for
+sockets.
 .ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
 .el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
 .IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
-This is not implemented yet (and might never be).
+This is not implemented yet (and might never be, unless you send me an
+implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets
+and is not embeddable, which would limit the usefulness of this backend
+immensely.
 .ie n .IP """EVBACKEND_PORT""    (value 32, Solaris 10)" 4
 .el .IP "\f(CWEVBACKEND_PORT\fR    (value 32, Solaris 10)" 4
 .IX Item "EVBACKEND_PORT    (value 32, Solaris 10)"
 This uses the Solaris 10 event port mechanism. As with everything on Solaris,
 it's really slow, but it still scales very well (O(active_fds)).
 .Sp
 Please note that solaris event ports can deliver a lot of spurious
 notifications, so you need to use non-blocking I/O or other means to avoid
 blocking when no data (or space) is available.
+.Sp
+While this backend scales well, it requires one system call per active
+file descriptor per loop iteration. For small and medium numbers of file
+descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend
+might perform better.
 .ie n .IP """EVBACKEND_ALL""" 4
 .el .IP "\f(CWEVBACKEND_ALL\fR" 4
 .IX Item "EVBACKEND_ALL"
 Try all backends (even potentially broken ones that wouldn't be tried
 with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as
 \&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR.
+.Sp
+It is definitely not recommended to use this flag.
 .RE
 .RS 4
 .Sp
 If one or more of these are ored into the flags value, then only these
 backends will be tried (in the reverse order as given here). If none are
 overhead for the actual polling but can deliver many events at once.
 .Sp
 By setting a higher \fIio collect interval\fR you allow libev to spend more
 time collecting I/O events, so you can handle more events per iteration,
 at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and
-\&\f(CW\*(C`ev_timer\*(C'\fR) will be not affected. Setting this to a non-null bvalue will
+\&\f(CW\*(C`ev_timer\*(C'\fR) will be not affected. Setting this to a non-null value will
 introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations.
 .Sp
 Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
 to spend more time collecting timeouts, at the expense of increased
 latency (the watcher callback will be called later). \f(CW\*(C`ev_io\*(C'\fR watchers
 In general you can register as many read and/or write event watchers per
 fd as you want (as long as you don't confuse yourself). Setting all file
 descriptors to non-blocking mode is also usually a good idea (but not
 required if you know what you are doing).
 .PP
-You have to be careful with dup'ed file descriptors, though. Some backends
-(the linux epoll backend is a notable example) cannot handle dup'ed file
-descriptors correctly if you register interest in two or more fds pointing
-to the same underlying file/socket/etc. description (that is, they share
-the same underlying \*(L"file open\*(R").
-.PP
 If you must do this, then force the use of a known-to-be-good backend
 (at the time of this writing, this includes only \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and
 \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR).
 .PP
 Another thing you have to watch out for is that it is quite easy to
 .PP
 \fIThe special problem of dup'ed file descriptors\fR
 .IX Subsection "The special problem of dup'ed file descriptors"
 .PP
 Some backends (e.g. epoll), cannot register events for file descriptors,
-but only events for the underlying file descriptions. That menas when you
+but only events for the underlying file descriptions. That means when you
-have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors and register events for them, only one
+have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register
-file descriptor might actually receive events.
+events for them, only one file descriptor might actually receive events.
 .PP
-There is no workaorund possible except not registering events
+There is no workaround possible except not registering events
-for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or to resort to
+for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
 \&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
 .PP
 \fIThe special problem of fork\fR
 .IX Subsection "The special problem of fork"
 .PP
 reader). Inotify will be used to give hints only and should not change the
 semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers, which means that libev sometimes needs
 to fall back to regular polling again even with inotify, but changes are
 usually detected immediately, and if the file exists there will be no
 polling.
+.PP
+\fIInotify\fR
+.IX Subsection "Inotify"
+.PP
+When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev (generally only
+available on Linux) and present at runtime, it will be used to speed up
+change detection where possible. The inotify descriptor will be created lazily
+when the first \f(CW\*(C`ev_stat\*(C'\fR watcher is being started.
+.PP
+Inotify presense does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
+except that changes might be detected earlier, and in some cases, to avoid
+making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presense of inotify support
+there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling.
+.PP
+(There is no support for kqueue, as apparently it cannot be used to
+implement this functionality, due to the requirement of having a file
+descriptor open on the object at all times).
+.PP
+\fIThe special problem of stat time resolution\fR
+.IX Subsection "The special problem of stat time resolution"
+.PP
+The \f(CW\*(C`stat ()\*(C'\fR syscall only supports full-second resolution portably, and
+even on systems where the resolution is higher, many filesystems still
+only support whole seconds.
+.PP
+That means that, if the time is the only thing that changes, you might
+miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and calls
+your callback, which does something. When there is another update within
+the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect it.
+.PP
+The solution to this is to delay acting on a change for a second (or till
+the next second boundary), using a roughly one-second delay \f(CW\*(C`ev_timer\*(C'\fR
+(\f(CW\*(C`ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)\*(C'\fR). The \f(CW.01\fR
+is added to work around small timing inconsistencies of some operating
+systems.
 .PP
 \fIWatcher-Specific Functions and Data Members\fR
 .IX Subsection "Watcher-Specific Functions and Data Members"
 .IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
 .IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
 The specified interval.
 .IP "const char *path [read\-only]" 4
 .IX Item "const char *path [read-only]"
 The filesystem path that is being watched.
 .PP
+\fIExamples\fR
+.IX Subsection "Examples"
+.PP
 Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
 .PP
 .Vb 15
 \&  static void
 \&  passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
 \&  ...
 \&  ev_stat passwd;
 .Ve
 .PP
 .Vb 2
-\&  ev_stat_init (&passwd, passwd_cb, "/etc/passwd");
+\&  ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
 \&  ev_stat_start (loop, &passwd);
+.Ve
+.PP
+Example: Like above, but additionally use a one-second delay so we do not
+miss updates (however, frequent updates will delay processing, too, so
+one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
+\&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
+.PP
+.Vb 2
+\&  static ev_stat passwd;
+\&  static ev_timer timer;
+.Ve
+.PP
+.Vb 4
+\&  static void
+\&  timer_cb (EV_P_ ev_timer *w, int revents)
+\&  {
+\&    ev_timer_stop (EV_A_ w);
+.Ve
+.PP
+.Vb 2
+\&    /* now it's one second after the most recent passwd change */
+\&  }
+.Ve
+.PP
+.Vb 6
+\&  static void
+\&  stat_cb (EV_P_ ev_stat *w, int revents)
+\&  {
+\&    /* reset the one-second timer */
+\&    ev_timer_again (EV_A_ &timer);
+\&  }
+.Ve
+.PP
+.Vb 4
+\&  ...
+\&  ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
+\&  ev_stat_start (loop, &passwd);
+\&  ev_timer_init (&timer, timer_cb, 0., 1.01);
 .Ve
 .ie n .Sh """ev_idle"" \- when you've got nothing better to do..."
 .el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do..."
 .IX Subsection "ev_idle - when you've got nothing better to do..."
 Idle watchers trigger events when no other events of the same or higher
 interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
 be detected at runtime.
 .IP "\s-1EV_H\s0" 4
 .IX Item "EV_H"
 The name of the \fIev.h\fR header file used to include it. The default if
-undefined is \f(CW\*(C`<ev.h>\*(C'\fR in \fIevent.h\fR and \f(CW"ev.h"\fR in \fIev.c\fR. This
+undefined is \f(CW"ev.h"\fR in \fIevent.h\fR and \fIev.c\fR. This can be used to
-can be used to virtually rename the \fIev.h\fR header file in case of conflicts.
+virtually rename the \fIev.h\fR header file in case of conflicts.
 .IP "\s-1EV_CONFIG_H\s0" 4
 .IX Item "EV_CONFIG_H"
 If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
 \&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
 \&\f(CW\*(C`EV_H\*(C'\fR, above.
 .IP "\s-1EV_EVENT_H\s0" 4
 .IX Item "EV_EVENT_H"
 Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea
-of how the \fIevent.h\fR header can be found.
+of how the \fIevent.h\fR header can be found, the dfeault is \f(CW"event.h"\fR.
 .IP "\s-1EV_PROTOTYPES\s0" 4
 .IX Item "EV_PROTOTYPES"
 If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
 prototypes, but still define all the structs and other symbols. This is
 occasionally useful if you want to provide your own wrapper functions
 pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR), usually more
 than enough. If you need to manage thousands of children you might want to
 increase this value (\fImust\fR be a power of two).
 .IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4
 .IX Item "EV_INOTIFY_HASHSIZE"
-\&\f(CW\*(C`ev_staz\*(C'\fR watchers use a small hash table to distribute workload by
+\&\f(CW\*(C`ev_stat\*(C'\fR watchers use a small hash table to distribute workload by
 inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR),
 usually more than enough. If you need to manage thousands of \f(CW\*(C`ev_stat\*(C'\fR
 watchers you might want to increase this value (\fImust\fR be a power of
 two).
 .IP "\s-1EV_COMMON\s0" 4
 .RS 4
 .IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4
 .IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)"
 This means that, when you have a watcher that triggers in one hour and
 there are 100 watchers that would trigger before that then inserting will
-have to skip those 100 watchers.
+have to skip roughly seven (\f(CW\*(C`ld 100\*(C'\fR) of these watchers.
-.IP "Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)" 4
+.IP "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 4
-.IX Item "Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)"
+.IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)"
-That means that for changing a timer costs less than removing/adding them
+That means that changing a timer costs less than removing/adding them
 as only the relative motion in the event queue has to be paid for.
 .IP "Starting io/check/prepare/idle/signal/child watchers: O(1)" 4
 .IX Item "Starting io/check/prepare/idle/signal/child watchers: O(1)"
 These just add the watcher into an array or at the head of a list.
+.IP "Stopping check/prepare/idle watchers: O(1)" 4
-=item Stopping check/prepare/idle watchers: O(1)
+.IX Item "Stopping check/prepare/idle watchers: O(1)"
+.PD 0
 .IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4
 .IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))"
+.PD
 These watchers are stored in lists then need to be walked to find the
 correct watcher to remove. The lists are usually short (you don't usually
 have many watchers waiting for the same fd or signal).
-.IP "Finding the next timer per loop iteration: O(1)" 4
+.IP "Finding the next timer in each loop iteration: O(1)" 4
-.IX Item "Finding the next timer per loop iteration: O(1)"
+.IX Item "Finding the next timer in each loop iteration: O(1)"
-.PD 0
+By virtue of using a binary heap, the next timer is always found at the
+beginning of the storage array.
 .IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4
 .IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)"
-.PD
 A change means an I/O watcher gets started or stopped, which requires
-libev to recalculate its status (and possibly tell the kernel).
+libev to recalculate its status (and possibly tell the kernel, depending
-.IP "Activating one watcher: O(1)" 4
+on backend and wether \f(CW\*(C`ev_io_set\*(C'\fR was used).
-.IX Item "Activating one watcher: O(1)"
+.IP "Activating one watcher (putting it into the pending state): O(1)" 4
+.IX Item "Activating one watcher (putting it into the pending state): O(1)"
 .PD 0
 .IP "Priority handling: O(number_of_priorities)" 4
 .IX Item "Priority handling: O(number_of_priorities)"
 .PD
 Priorities are implemented by allocating some space for each
 priority. When doing priority-based operations, libev usually has to
-linearly search all the priorities.
+linearly search all the priorities, but starting/stopping and activating
+watchers becomes O(1) w.r.t. prioritiy handling.
 .RE
 .RS 4
 .SH "AUTHOR"
 .IX Header "AUTHOR"
 Marc Lehmann <libev@schmorp.de>.

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Comparing libev/ev.3 (file contents): Revision 1.57 by root, Sat Dec 22 11:49:17 2007 UTC vs. Revision 1.59 by root, Tue Dec 25 07:16:53 2007 UTC

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Comparing libev/ev.3 (file contents):
Revision 1.57 by root, Sat Dec 22 11:49:17 2007 UTC vs.
Revision 1.59 by root, Tue Dec 25 07:16:53 2007 UTC