musl: read the timezone from /etc/TZ

Currently the OpenWRT boot scripts write the timezone configuration to
/tmp/TZ, relying on the behaviour of uClibc that the timezone is read
from /etc/TZ if no TZ env variable is found.

This works because /etc/TZ is a symlink to /tmp/TZ.

Musl libc however only reads the timezone from the TZ env variable and
if it doesn't find it or it's empty, it will look for a zoneinfo
file, that doesn't exist.

So in musl builds no timezone is ever set.

This patch fixes the issue by having musl libc behave like uClibc: if no
TZ env variable is found it will try to load it from /etc/TZ.

Signed-off-by: Gianluca Anzolin <gianluca at sottospazio.it>
Signed-off-by: Felix Fietkau <nbd@openwrt.org>

SVN-Revision: 46069

toolchain/musl/patches/110-read_timezone_from_fs.patch

@@ -0,0 +1,28 @@
+--- a/src/time/__tz.c
++++ b/src/time/__tz.c
+@@ -23,6 +23,9 @@ static int r0[5], r1[5];
+ static const unsigned char *zi, *trans, *index, *types, *abbrevs, *abbrevs_end;
+ static size_t map_size;
+ 
++static const char *tzfile;
++static size_t tzfile_size;
++
+ static char old_tz_buf[32];
+ static char *old_tz = old_tz_buf;
+ static size_t old_tz_size = sizeof old_tz_buf;
+@@ -125,6 +128,15 @@ static void do_tzset()
+ 		"/usr/share/zoneinfo/\0/share/zoneinfo/\0/etc/zoneinfo/\0";
+ 
+ 	s = getenv("TZ");
++
++	/* if TZ is empty try to read it from /etc/TZ */
++	if (!s || !*s) {
++		if (tzfile)
++			__munmap((void*)tzfile, tzfile_size);
++
++		s = tzfile = (void *)__map_file("/etc/TZ", &tzfile_size);
++	}
++
+ 	if (!s || !*s) s = "/etc/localtime";
+ 
+ 	if (old_tz && !strcmp(s, old_tz)) return;