[libvirt] [PATCHv3 1/4] util: new function virTimeLocalOffsetFromUTC
Laine Stump
laine at laine.org
Fri May 23 19:49:11 UTC 2014
Since there isn't a single libc API to get this value, this patch
supplies one which gets the value by grabbing current UTC, then
converting that into a struct tm with localtime_r(), then back to a
time_t using mktime; it again does the same operation, but using
gmtime_r() instead (for UTC). It then subtracts utc time from the
localtime, and finally adjusts if daylight savings time (DST) is set
in the localtime timeinfo (because for some reason mktime doesn't take
that into account).
The returned value is the difference between UTC and localtime in
seconds. If localtime is ahead of UTC (east) the offset will be a
positive number, and if localtime is behind UTC (west) the offset will
be negative.
This function should be POSIX-compliant, and is threadsafe, but not
async signal safe. If it was ever necessary to know this value in a
child process, we could cache it with a one-time init function when
libvirtd starts, then just supply the cached value, but that
complexity isn't needed for current usage.
Note that it is theoretically possible to set a DST offset that is not
exactly one hour. This function doesn't handle that (is that actually
in use anywhere?)
(If it weren't for DST, we could simply replace this entire function
with "-timezone"; timezone contains the offset of the current timezone
(negated from what we want) but doesn't account for DST. And in spite
of being guaranteed by POSIX, it isn't available on older versions of
mingw.)
---
Change from V2:
* added test cases that force DST to be active so that the "tm_isdst"
logic can be properly tested.
* addressed Eric's review points.
Note that I tried out using the global "timezone", but it doesn't
adjust for DST, so I decided to keep a single implementation of the
function.
src/libvirt_private.syms | 1 +
src/util/virtime.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++-
src/util/virtime.h | 5 +++--
tests/virtimetest.c | 51 ++++++++++++++++++++++++++++++++++++++++++++++++
4 files changed, 104 insertions(+), 3 deletions(-)
diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
index c3332c9..cb635cd 100644
--- a/src/libvirt_private.syms
+++ b/src/libvirt_private.syms
@@ -1984,6 +1984,7 @@ virTimeFieldsNow;
virTimeFieldsNowRaw;
virTimeFieldsThen;
virTimeFieldsThenRaw;
+virTimeLocalOffsetFromUTC;
virTimeMillisNow;
virTimeMillisNowRaw;
virTimeStringNow;
diff --git a/src/util/virtime.c b/src/util/virtime.c
index caa4e24..79b7bd5 100644
--- a/src/util/virtime.c
+++ b/src/util/virtime.c
@@ -1,7 +1,7 @@
/*
* virtime.c: Time handling functions
*
- * Copyright (C) 2006-2012 Red Hat, Inc.
+ * Copyright (C) 2006-2014 Red Hat, Inc.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
@@ -344,3 +344,51 @@ char *virTimeStringThen(unsigned long long when)
return ret;
}
+
+/**
+ * virTimeLocalOffsetFromUTC:
+ *
+ * This function is threadsafe, but is *not* async signal safe (due to
+ * localtime_r()).
+ *
+ * @offset: pointer to time_t that will be set to the difference
+ * between localtime and UTC in seconds (east of UTC is a
+ * positive number, and west of UTC is a negative number.
+ *
+ * Returns 0 on success, -1 on error with error reported
+ */
+int
+virTimeLocalOffsetFromUTC(long *offset)
+{
+ struct tm gmtimeinfo, localtimeinfo;
+ time_t current, utc, local;
+
+ if ((current = time(NULL)) == (time_t)-1) {
+ virReportSystemError(errno, "%s",
+ _("failed to get current system time"));
+ return -1;
+ }
+
+ if (!localtime_r(¤t, &localtimeinfo)) {
+ virReportSystemError(errno, "%s",
+ _("localtime_r failed"));
+ return -1;
+ }
+ if (!gmtime_r(¤t, &gmtimeinfo)) {
+ virReportSystemError(errno, "%s",
+ _("gmtime_r failed"));
+ return -1;
+ }
+
+ if ((local = mktime(&localtimeinfo)) == (time_t)-1 ||
+ (utc = mktime(&gmtimeinfo)) == (time_t)-1) {
+ virReportSystemError(errno, "%s",
+ _("mktime failed"));
+ return -1;
+ }
+
+ *offset = local - utc;
+ if (localtimeinfo.tm_isdst)
+ *offset += 3600;
+ return 0;
+}
diff --git a/src/util/virtime.h b/src/util/virtime.h
index a5bd652..25332db 100644
--- a/src/util/virtime.h
+++ b/src/util/virtime.h
@@ -1,7 +1,7 @@
/*
* virtime.h: Time handling functions
*
- * Copyright (C) 2006-2011 Red Hat, Inc.
+ * Copyright (C) 2006-2011, 2014 Red Hat, Inc.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
@@ -50,7 +50,6 @@ int virTimeStringNowRaw(char *buf)
int virTimeStringThenRaw(unsigned long long when, char *buf)
ATTRIBUTE_NONNULL(2) ATTRIBUTE_RETURN_CHECK;
-
/* These APIs are *not* async signal safe and return -1,
* raising a libvirt error on failure
*/
@@ -63,5 +62,7 @@ int virTimeFieldsThen(unsigned long long when, struct tm *fields)
char *virTimeStringNow(void);
char *virTimeStringThen(unsigned long long when);
+int virTimeLocalOffsetFromUTC(long *offset)
+ ATTRIBUTE_NONNULL(1) ATTRIBUTE_RETURN_CHECK;
#endif
diff --git a/tests/virtimetest.c b/tests/virtimetest.c
index 73a3c3e..a14dcb9 100644
--- a/tests/virtimetest.c
+++ b/tests/virtimetest.c
@@ -72,6 +72,35 @@ static int testTimeFields(const void *args)
}
+typedef struct {
+ const char *zone;
+ long offset;
+} testTimeLocalOffsetData;
+
+static int
+testTimeLocalOffset(const void *args)
+{
+ const testTimeLocalOffsetData *data = args;
+ long actual;
+
+ if (setenv("TZ", data->zone, 1) < 0) {
+ perror("setenv");
+ return -1;
+ }
+ tzset();
+
+ if (virTimeLocalOffsetFromUTC(&actual) < 0) {
+ return -1;
+ }
+
+ if (data->offset != actual) {
+ VIR_DEBUG("Expect Offset %ld got %ld\n",
+ data->offset, actual);
+ return -1;
+ }
+ return 0;
+}
+
static int
mymain(void)
{
@@ -119,6 +148,28 @@ mymain(void)
TEST_FIELDS(2147483648000ull, 2038, 1, 19, 3, 14, 8);
+#define TEST_LOCALOFFSET(tz, off) \
+ do { \
+ testTimeLocalOffsetData data = { \
+ .zone = tz, \
+ .offset = off, \
+ }; \
+ if (virtTestRun("Test localtime offset for " #tz, \
+ testTimeLocalOffset, &data) < 0) \
+ ret = -1; \
+ } while (0)
+
+ TEST_LOCALOFFSET("VIR00:30", -30 * 60);
+ TEST_LOCALOFFSET("VIR01:30", -90 * 60);
+ TEST_LOCALOFFSET("UTC", 0);
+ TEST_LOCALOFFSET("VIR-00:30", 30 * 60);
+ TEST_LOCALOFFSET("VIR-01:30", 90 * 60);
+ /* test DST processing with timezones that always
+ * have DST in effect
+ */
+ TEST_LOCALOFFSET("VIR-00:30VID,0,365", 90 * 60);
+ TEST_LOCALOFFSET("VIR-02:30VID,0,365", 210 * 60);
+
return ret == 0 ? EXIT_SUCCESS : EXIT_FAILURE;
}
--
1.9.0
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