On Wed, 1 Sep 2021 06:45:26 GMT, Wu Yan <wu...@openjdk.org> wrote: > Hi, > Please help me review the change to enhance getting time zone ID from > /etc/localtime on linux. > > We use `realpath` instead of `readlink` to obtain the link name of > /etc/localtime, because `readlink` can only read the value of a symbolic of > link, not the canonicalized absolute pathname. > > For example, the value of /etc/localtime is > "../usr/share/zoneinfo//Asia/Shanghai", then the linkbuf obtained by > `readlink` is "../usr/share/zoneinfo//Asia/Shanghai", and then the call of > `getZoneName(linkbuf)` will get "/Asia/Shanghai", not "Asia/Shanghai", which > consider as invalid in `ZoneInfoFile.getZoneInfo()`. Using `realpath`, you > can get “/usr/share/zoneinfo/Asia/Shanghai“ directly from “/etc/localtime“. > > Thanks, > wuyan
Using `realpath` instead of `readlink` will change results on systems which use symbolic links instead of hard links to de-duplicate the timezone files. For example, on Debian, if `UTC` is configured (`/etc/localtime` points to `/usr/share/zoneinfo/UTC`), I think the result will be `Etc/UTC` instead of `UTC` after this change. But I have not actually tested this. src/java.base/unix/native/libjava/TimeZone_md.c line 292: > 290: /* canonicalize the path */ > 291: char resolvedpath[PATH_MAX + 1]; > 292: char *path = realpath(DEFAULT_ZONEINFO_FILE, resolvedpath); You really should use `realpath` with `NULL` as the second argument, to avoid any risk of buffer overflow. Future C library headers may warn about non-null arguments here. ------------- PR: https://git.openjdk.java.net/jdk/pull/5327
