can add mmap file api?

[mei-rune]

mmap file is very important for the server, can add it to os package.

like https://github.com/edsrzf/mmap-go

[minux]

The syscall package contains Mmap and related syscalls. I don't think a portable memory mapped file facility needs to live inside the standard library. A go-gettable package is perfectly fine.

[ianlancetaylor]

I agree with minux: in syscall is sufficient.