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Added follow-file-timestamp mode via FAKETIME='%' and FAKETIME_FOLLOW_FILE (#156)

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Wolfgang Hommel
2019-08-20 19:43:15 +02:00
parent e85863f671
commit 57917c4d5a
2 changed files with 68 additions and 0 deletions
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40
README
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@@ -205,6 +205,22 @@ specified absolute time. The 'start at' format allows a 'relative' clock
operation as described below in section 4d), but using a 'start at' time
instead of an offset time.
If the started process itself starts other (child) processes, they by default
will start with the specified start-at-date again. If this is not what you need,
set the environment variable FAKETIME_DONT_RESET=1. Try these examples to see
the difference:
LD_PRELOAD=src/libfaketime.so.1 FAKETIME="@2000-01-01 11:12:13" \
FAKETIME_DONT_RESET=1 \
/bin/bash -c 'while [ $SECONDS -lt 5 ]; do date; sleep 1; done'
LD_PRELOAD=src/libfaketime.so.1 FAKETIME="@2000-01-01 11:12:13" \
/bin/bash -c 'while [ $SECONDS -lt 5 ]; do date; sleep 1; done'
In the second example, the "date" command will always print the same time,
while in the first example, with FAKETIME_DONT_RESET set, time will increment
even though all the "date" commands are new processes.
4d) Using offsets for relative dates
------------------------------------
@@ -336,6 +352,30 @@ with FAKETIME_NO_CACHE=1. Remember that disabling the cache may negatively
influence the performance.
Setting FAKETIME by means of a file timestamp
---------------------------------------------
Based on a proposal by Hitoshi Harada (umitanuki), the "start at" time can now be
set through any file in the file system by setting the FAKETIME environment variable
to "%" (a percent sign) and FAKETIME_FOLLOW_FILE to the name of the file whose
modification timestamp shall be used as source for the "start at" time.
Usage example:
# create any file with December 24th, 2009, 12:34:56 as timestamp
touch -t 0912241234.56 /tmp/my-demo-file.tmp
# run a bash shell with an endless loop printing the current time
LD_PRELOAD=/path/to/libfaketime.so.1 \
FAKETIME='%' FAKETIME_FOLLOW_FILE=/tmp/my-demo-file.tmp \
FAKETIME_DONT_RESET=1 \
bash -c 'while true ; do date ; sleep 1 ; done'
# now, while the above is running, change the file's timestamp
# (in a different terminal window or whatever)
touch -t 2002290123.45 /tmp/my-demo-file.tmp
4f) Faking the date and time system-wide
----------------------------------------

28
src/libfaketime.c
View File

@@ -1794,6 +1794,34 @@ static void parse_ft_string(const char *user_faked_time)
goto parse_modifiers;
break;
case '%': /* follow file timestamp as suggested by Hitoshi Harada (umitanuki) */
ft_mode = FT_START_AT;
struct stat master_file_stats;
int ret;
if (NULL == getenv("FAKETIME_FOLLOW_FILE"))
{
fprintf(stderr, "libfaketime: %% operator in FAKETIME setting requires environment variable FAKETIME_FOLLOW_FILE set.\n");
exit(1);
}
else
{
DONT_FAKE_TIME(ret = stat(getenv("FAKETIME_FOLLOW_FILE"), &master_file_stats));
if (ret == -1)
{
fprintf(stderr, "libfaketime: Cannot get timestamp of file %s as requested by %% operator.\n", getenv("FAKETIME_FOLLOW_FILE"));
exit(1);
}
else
{
user_faked_time_timespec.tv_sec = master_file_stats.st_mtime;
user_faked_time_timespec.tv_nsec = 0;
}
}
if (NULL == getenv("FAKETIME_DONT_RESET"))
system_time_from_system(&ftpl_starttime);
goto parse_modifiers;
break;
case 'i':
case 'x': /* Only modifiers are passed, don't fall back to strptime */
parse_modifiers: