I’m assuming that by “btime”, you mean “birth time”, or “file creation time”. You’re right, POSIX doesn’t specify that currently, and there is no mention of “btime” in the standard, even in the current 202x draft. It does mention “file creation time”, once, in relation to
As mentioned in roaima’s answer, the standard does allow additional fields to be added to
struct stat. Some platforms have eschewed that however; on Linux for example the file creation time is available in
struct statx, which is returned by the
statx function. Adding fields to
struct stat itself would create a risk of conflict with future issues of the standard.
If you want to change that, you’ll need to get involved with the Austin Group, which is in charge of updating POSIX. You should plan on dedicating quite a lot of time to familiarise yourself with its way of working, and to participate passively before suggesting changes. You could start by looking at how the standard currently defines the existing timestamps, and where they are mentioned (including every single function which results in updating them).
Note that to a large extent, POSIX isn’t the right venue to drive change; it tends to document features and normalise them once they are supported somewhere and have proven themselves useful.