runtime: move epoll syscalls to runtime/internal/syscall

This change moves Linux epoll's syscalls implementation to the
"runtime/internal/syscall" package. The intention in this CL was to
minimise behavioural changes but make the code more generalised. This
also will allow adding new syscalls (like epoll_pwait2) without the
need to implement assembly stubs for each arch.

It also drops epoll_create as not all architectures provide this call.
epoll_create1 was added to the kernel in version 2.6.27 and Go requires
Linux kernel version 2.6.32 or later since Go 1.18. So it is safe to
always use epoll_create1.

This is a resubmit as the previous CL 421994 was reverted due to test
failures after the merge with the master. The issue was fixed in
CL 438615

For #53824
For #51087

Change-Id: I1bd0f23a85b4f9b80178c5dd36fd3e95ff4f9648
Reviewed-on: https://go-review.googlesource.com/c/go/+/440115
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Michael Pratt <mpratt@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
Run-TryBot: Michael Pratt <mpratt@google.com>

1 files changed, 28 insertions, 1 deletions

diff --git a/src/runtime/internal/syscall/syscall_linux.go b/src/runtime/internal/syscall/syscall_linux.go
index 7f268e8fba..a103d318c4 100644
--- a/src/runtime/internal/syscall/syscall_linux.go
+++ b/src/runtime/internal/syscall/syscall_linux.go
@@ -6,7 +6,7 @@
 package syscall
 
 import (
-	_ "unsafe" // for go:linkname
+	"unsafe"
 )
 
 // TODO(https://go.dev/issue/51087): This package is incomplete and currently
@@ -37,3 +37,30 @@ func Syscall6(num, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2, errno uintptr)
 func syscall_RawSyscall6(num, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2, errno uintptr) {
 	return Syscall6(num, a1, a2, a3, a4, a5, a6)
 }
+
+func EpollCreate1(flags int32) (fd int32, errno uintptr) {
+	r1, _, e := Syscall6(SYS_EPOLL_CREATE1, uintptr(flags), 0, 0, 0, 0, 0)
+	return int32(r1), e
+}
+
+var _zero uintptr
+
+func EpollWait(epfd int32, events []EpollEvent, maxev, waitms int32) (n int32, errno uintptr) {
+	var ev unsafe.Pointer
+	if len(events) > 0 {
+		ev = unsafe.Pointer(&events[0])
+	} else {
+		ev = unsafe.Pointer(&_zero)
+	}
+	r1, _, e := Syscall6(SYS_EPOLL_PWAIT, uintptr(epfd), uintptr(ev), uintptr(maxev), uintptr(waitms), 0, 0)
+	return int32(r1), e
+}
+
+func EpollCtl(epfd, op, fd int32, event *EpollEvent) (errno uintptr) {
+	_, _, e := Syscall6(SYS_EPOLL_CTL, uintptr(epfd), uintptr(op), uintptr(fd), uintptr(unsafe.Pointer(event)), 0, 0)
+	return e
+}
+
+func CloseOnExec(fd int32) {
+	Syscall6(SYS_FCNTL, uintptr(fd), F_SETFD, FD_CLOEXEC, 0, 0, 0)
+}