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settime functions support FAKETIME_UPDATE_TIMESTAMP_FILE (for #239).

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When the environment variable FAKETIME_TIMESTAMP_FILE is set, points to
a writeable (creatable) custom config file and the environment variable
FAKETIME_UPDATE_TIMESTAMP_FILE is "1", then the file also is updated on
each call. By this, a common "virtual time" can be shared by several
processes, where each can adjust the time for all.
This commit is contained in:
Steffen Dettmer
2020-04-09 15:54:23 +02:00
parent 1e25e1f042
commit c1d10321a7
3 changed files with 108 additions and 8 deletions
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6
NEWS
View File

@@ -1,3 +1,9 @@
- When the environment variable FAKETIME_TIMESTAMP_FILE is
set, points to a writeable (creatable) custom config file
and the environment variable FAKETIME_UPDATE_TIMESTAMP_FILE
is "1", then the file also is updated on each call. By
this, a common "virtual time" can be shared by several
processes, where each can adjust the time for all.
- Additional link-time LDFLAGS can be passed via the
environment variable FAKETIME_LINK_FLAGS when
running 'make'.

74
README
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@@ -187,19 +187,21 @@ linker configuration file, e.g., /etc/ld.so.conf.d/local.conf, and then run
the "ldconfig" command. Afterwards, using LD_PRELOAD=libfaketime.so.1 suffices.
However, also the faked time should be specified; otherwise, libfaketime will
be loaded, but just report the real system time. There are three ways to
be loaded, but just report the real system time. There are multiple ways to
specify the faked time:
a) By setting the environment variable FAKETIME.
b) By using the file given in the environment variable FAKETIME_TIMESTAMP_FILE
c) By using the file .faketimerc in your home directory.
d) By using the file /etc/faketimerc for a system-wide default.
e) By using FAKETIME_UPDATE_TIMESTAMP_FILE and date -s "<time>" or alike.
If you want to use b) c) or d), $HOME/.faketimerc or /etc/faketimerc consist of
only one line of text with exactly the same content as the FAKETIME environment
variable, which is described below. Note that /etc/faketimerc will only be used
if there is no $HOME/.faketimerc and no FAKETIME_TIMESTAMP_FILE file exists.
Also, the FAKETIME environment variable _always_ has priority over the files.
For FAKETIME_UPDATE_TIMESTAMP_FILE please see below.
4b) Using absolute dates
@@ -368,7 +370,8 @@ may take up to 10 seconds before the new fake time is applied. If this is a
problem in your scenario, you can change number of seconds before the file is read
again with environment variable FAKETIME_CACHE_DURATION, or disable caching at all
with FAKETIME_NO_CACHE=1. Remember that disabling the cache may negatively
influence the performance.
influence the performance (especially when not using FAKETIME environment
but configuration files, such as FAKETIME_TIMESTAMP_FILE).
Setting FAKETIME by means of a file timestamp
@@ -434,9 +437,14 @@ Cleaning up shared memory
-------------------------
libfaketime uses semaphores and shared memory on platforms that support it in
order to sync faketime settings across parent-child processes. It will clean
up when it exits properly. However, when processes are terminated (e.g., by
Ctrl-C on command line), shared memory cannot be cleaned up properly. In such
order to sync faketime settings across parent-child processes.
Please note that this does not share the time set by settimeofday (for that
see FAKETIME_UPDATE_TIMESTAMP_FILE below).
libfaketime will clean up when it exits properly.
However, when processes are terminated (e.g., by Ctrl-C on command line),
shared memory cannot be cleaned up properly. In such
cases, you should occasionally delete
/dev/shm/faketime_shm_* and
@@ -461,9 +469,54 @@ Intercepting time-setting calls
libfaketime can be compiled with the CFLAG "-DFAKE_SETTIME" in order
to also intercept time-setting functions, i.e., clock_settime(),
settimeofday(), and adjtime(). Instead of passing the timestamp a
program sets through to the system, only the FAKETIME environment
variable will be adjusted accordingly.
settimeofday(), and adjtime(). The FAKETIME environment
variable will be adjusted on each call.
When the environment variable FAKETIME_TIMESTAMP_FILE is set, points to a
writeable (creatable) custom config file and the environment variable
FAKETIME_UPDATE_TIMESTAMP_FILE is "1", then the file also is updated on each
call. By this, a common "virtual time" can be shared by several
processes, where each can adjust the time for all.
Sharing "virtual settable time" between independent processes
-------------------------------------------------------------
When libfaketime was compiled with FAKETIME_COMPILE_CFLAGS="-DFAKE_SETTIME",
it can be configured to support a common time offset for multiple processes.
This for example allows to use "ntpdate" as normal user without affecting
system clock, interactively testing software with different dates or testing
complex software with multiple independent processes that themself use
settime internally.
Examples:
$ export LD_PRELOAD=libfaketime.so.1
$ export FAKETIME_TIMESTAMP_FILE="/tmp/my-faketime.rc"
$ export FAKETIME_UPDATE_TIMESTAMP_FILE=1
$ export FAKETIME_CACHE_DURATION=1 # in seconds
# or: export FAKETIME_NO_CACHE=1
$ date -s "1999-12-24 16:00:00"
Fri Dec 24 16:00:00 CET 1999
$ LD_PRELOAD="" date
Thu Apr 9 15:19:38 CEST 2020
$ date
Fri Dec 24 16:00:02 CET 1999
$ /usr/sbin/ntpdate -u clock.isc.org
9 Apr 15:18:37 ntpdate[718]: step time server xx offset 640390517.057257 sec
$ date
Thu Apr 9 15:18:40 CEST 2020
In another terminal, script or environmment the same variables could be set
and the same time would be printed.
This also avoid the need to directly update the rc config file to use
different times, but of course only supports time offsets.
Please note that this feature is not compatible with several other features,
such as FAKETIME_FOLLOW_FILE, FAKETIME_XRESET and maybe others. After first
settime, offsets will be used in FAKETIME_TIMESTAMP_FILE, even if it
initially used advanced time specification options.
4f) Faking the date and time system-wide
@@ -639,6 +692,11 @@ seconds.
4k) Saving timestamps to file, loading them from file
-----------------------------------------------------
To store and load timestamp _offsets_ using _one and the same_ file allowing
to share a common "virtual time" between independent processes, please see
FAKETIME_UPDATE_TIMESTAMP_FILE above. The FAKETIME_SAVE_FILE feature is
different.
faketime can save faked timestamps to a file specified by FAKETIME_SAVE_FILE
environment variable. It can also use the file specified by FAKETIME_LOAD_FILE
to replay timestamps from it. After consuming the whole file, libfaketime

36
src/libfaketime.c
View File

@@ -3408,6 +3408,42 @@ int clock_settime(clockid_t clk_id, const struct timespec *tp) {
setenv("FAKETIME", newenv_string, 1);
force_cache_expiration = 1; /* make sure it becomes effective immediately */
/* If FAKETIME_TIMESTAMP_FILE was given in environment,
* and if FAKETIME_UPDATE_TIMESTAMP_FILE=1, then update it.
* This allows other process instances to share the same time. */
if ( (getenv("FAKETIME_TIMESTAMP_FILE") != NULL)
&& (*getenv("FAKETIME_TIMESTAMP_FILE") != '\0')
&& (getenv("FAKETIME_UPDATE_TIMESTAMP_FILE") != NULL)
&& (strcmp(getenv("FAKETIME_UPDATE_TIMESTAMP_FILE"), "1") == 0))
{
const char *error = NULL;
FILE *envfile;
static char custom_filename[BUFSIZ];
(void) snprintf(custom_filename, BUFSIZ, "%s", getenv("FAKETIME_TIMESTAMP_FILE"));
if ((envfile = fopen(custom_filename, "wt")) != NULL)
{
if (fprintf(envfile, "%+f\n", offset) < 0)
{
error = "to write to file";
}
if (fclose(envfile) != 0)
{
error = "to close file";
}
}
else
{
error = "to open file";
}
if (error)
{
fprintf(stderr, "libfaketime: In clock_settime(), failed to "
"%s while updating FAKETIME_TIMESTAMP_FILE (`%s'): %s\n",
error, getenv("FAKETIME_TIMESTAMP_FILE"), strerror(errno));
}
}
return 0;
}