That seems to be fundamentally impossible on posix using only syscalls, but
you may be able to use /proc:
https://manpages.debian.org/stretch/manpages-dev/umask.2.en.html#NOTES
On Tue, Nov 6, 2018 at 4:35 PM Tom Payne <twpa...@gmail.com> wrote:
> Hi,
>
> The user's umask can be set with the umask(2) system call, this sets the
> new umask and returns the old one. As far as I can tell, the canonical way
> to get the user's current umask is to call umask twice: once to get the old
> value and set a temporary one, then a second call to restore the old value:
>
> func getUmask() int {
> umask := syscall.Umask(0)
> syscall.Umask(umask)
> return umask
> }
>
> This has an obvious race condition: if some file operations (e.g. mkdir or
> open) occur between the two calls to syscall.Umask then they will use the
> unwanted temporary umask value.
>
> How can I avoid this race condition?
>
> One heavyweight possibility is to read the umask during the main package's
> init, including a call to runtime.LockOSThread(). However, I'd like to be
> able to call my getUmask() function at any time.
>
> Many thanks for any pointers,
> Tom
>
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