syscall, x/sys/unix: ustat is deprecated and has been removed from glibc

[fweimer]

src/syscall/types_linux.go includes <ustat.h>. The ustat system call was deprecated well before Go development started, and the ustat manual page said so since basically forever.

glibc 2.28 will remove the header file, so Go will no longer build. Seen so far with libgo on the GCC branch gcc-8-branch. Go 1.0.3 itself still appears to build. However, I think it makes sense to remove this interface upstream as well.

[agnivade]

/cc @ianlancetaylor , @tklauser

[tklauser]

<ustat.h> is included in src/syscall/types_linux.go only to generate the syscall wrapper functions, types and constants. It's not used in the build itself, so the build won't break event if glibc remove the header. But we will no longer be able to (re-)generate the wrappers.

In golang.org/x/sys/unix (which should be used instead of syscall outside the standard library anyhow) https://golang.org/cl/119655 just recently deprecated Ustat for linux/arm64 and I think we should do the same for all other GOARCHes.

About syscall I'm not sure. I think we might want to return ENOSYS, but removing the function would probably break the Go 1 compatibility promise. In any case, I'll let @ianlancetaylor decide on that one.

[tklauser]

We might even remove Ustat from golang.org/x/sys/unix altogether IMO. The Go 1 compatibility promise doesn't apply there.

[gopherbot]

Change https://golang.org/cl/120295 mentions this issue: unix: remove Ustat on Linux

[awilfox]

Just to chime in from the musl side, musl has never shipped a <ustat.h>, which did not break the build of GCC's libgo here, but caused an error during linking:

../powerpc-foxkit-linux-musl/libgo/.libs/libgo.so: undefined reference to `ustat'

I think that if glibc actually removes the symbol, not just the header, then there will be further pain in GCC libgo.

[fweimer]

glibc 2.28 will remove the symbol in the sense that new binaries can no longer link, so there's a link failure with libgo.so as well.

[gopherbot]

Change https://golang.org/cl/120535 mentions this issue: syscall: remove Ustat