Allow searching $TZDIR for timezone data

glibc supports the environment variable as additional search path, means
we allow to override the `/usr/share/zoneinfo` path by setting the
variable.

Analogous change to containers/common#1772

Signed-off-by: Sascha Grunert <sgrunert@redhat.com>

docs/source/markdown/options/tz.md

@@ -4,5 +4,5 @@
 ####> are applicable to all of those.
 #### **--tz**=*timezone*
 
-Set timezone in container. This flag takes area-based timezones, GMT time, as well as `local`, which sets the timezone in the container to match the host machine. See `/usr/share/zoneinfo/` for valid timezones.
+Set timezone in container. This flag takes area-based timezones, GMT time, as well as `local`, which sets the timezone in the container to match the host machine. See `/usr/share/zoneinfo/` for valid timezones. Podman honors the `$TZDIR` environment variable to modify the `/usr/share/zoneinfo` search path for valid timezones.
 Remote connections use local containers.conf for defaults

libpod/container_internal.go

@@ -1708,6 +1708,14 @@ func (c *Container) mountStorage() (_ string, deferredErr error) {
  tz := c.Timezone()
  if tz != "" {
  timezonePath := filepath.Join("/usr/share/zoneinfo", tz)
+
+ // Allow using TZDIR per:
+ // https://sourceware.org/git/?p=glibc.git;a=blob;f=time/tzfile.c;h=8a923d0cccc927a106dc3e3c641be310893bab4e;hb=HEAD#l149
+ tzdir := os.Getenv("TZDIR")
+ if tzdir != "" {
+ timezonePath = filepath.Join(tzdir, tz)
+ }
+
  if tz == "local" {
  timezonePath, err = filepath.EvalSymlinks("/etc/localtime")
  if err != nil {