internal/syscall/unix: add KernelVersionGE

There are a few places in the code which checks that the running kernel
is greater than or equal to x.y. The check takes a few lines and the
checking code is somewhat distracting.

Let's abstract this check into a simple function, KernelVersionGE,
and convert the users accordingly.

Add a test case (I'm not sure it has much value, can be dropped).

Change-Id: I8ec91dcc7452363361f95e46794701c0ae57d956
Reviewed-on: https://go-review.googlesource.com/c/go/+/700796
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Damien Neil <dneil@google.com>
Reviewed-by: Mark Freeman <markfreeman@google.com>

4 files changed, 87 insertions, 7 deletions

diff --git a/src/internal/syscall/unix/kernel_version_freebsd.go b/src/internal/syscall/unix/kernel_version_freebsd.go
index ef9ee136f3..db3519ddfb 100644
--- a/src/internal/syscall/unix/kernel_version_freebsd.go
+++ b/src/internal/syscall/unix/kernel_version_freebsd.go
@@ -42,7 +42,9 @@ func KernelVersion() (major, minor int) {
 // This function will examine both the kernel version and the availability of the system call.
 var SupportCopyFileRange = sync.OnceValue(func() bool {
 	// The copy_file_range() function first appeared in FreeBSD 13.0.
-	major, _ := KernelVersion()
+	if !KernelVersionGE(13, 0) {
+		return false
+	}
 	_, err := CopyFileRange(0, nil, 0, nil, 0, 0)
-	return major >= 13 && err != syscall.ENOSYS
+	return err != syscall.ENOSYS
 })
diff --git a/src/internal/syscall/unix/kernel_version_ge.go b/src/internal/syscall/unix/kernel_version_ge.go
new file mode 100644
index 0000000000..a142404199
--- /dev/null
+++ b/src/internal/syscall/unix/kernel_version_ge.go
@@ -0,0 +1,13 @@
+// Copyright 2025 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package unix
+
+// KernelVersionGE checks if the running kernel version
+// is greater than or equal to the provided version.
+func KernelVersionGE(x, y int) bool {
+	xx, yy := KernelVersion()
+
+	return xx > x || (xx == x && yy >= y)
+}
diff --git a/src/internal/syscall/unix/kernel_version_ge_test.go b/src/internal/syscall/unix/kernel_version_ge_test.go
new file mode 100644
index 0000000000..f4b1b23cd2
--- /dev/null
+++ b/src/internal/syscall/unix/kernel_version_ge_test.go
@@ -0,0 +1,67 @@
+// Copyright 2025 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package unix_test
+
+import (
+	"internal/syscall/unix"
+	"testing"
+)
+
+func TestKernelVersionGE(t *testing.T) {
+	major, minor := unix.KernelVersion()
+	t.Logf("Running on kernel %d.%d", major, minor)
+
+	tests := []struct {
+		name string
+		x, y int
+		want bool
+	}{
+		{
+			name: "current version equals itself",
+			x:    major,
+			y:    minor,
+			want: true,
+		},
+		{
+			name: "older major version",
+			x:    major - 1,
+			y:    0,
+			want: true,
+		},
+		{
+			name: "same major, older minor version",
+			x:    major,
+			y:    minor - 1,
+			want: true,
+		},
+		{
+			name: "newer major version",
+			x:    major + 1,
+			y:    0,
+			want: false,
+		},
+		{
+			name: "same major, newer minor version",
+			x:    major,
+			y:    minor + 1,
+			want: false,
+		},
+		{
+			name: "min version (0.0)",
+			x:    0,
+			y:    0,
+			want: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := unix.KernelVersionGE(tt.x, tt.y)
+			if got != tt.want {
+				t.Errorf("KernelVersionGE(%d, %d): got %v, want %v", tt.x, tt.y, got, tt.want)
+			}
+		})
+	}
+}
diff --git a/src/internal/syscall/unix/kernel_version_solaris.go b/src/internal/syscall/unix/kernel_version_solaris.go
index 3f399411d7..7904e1f429 100644
--- a/src/internal/syscall/unix/kernel_version_solaris.go
+++ b/src/internal/syscall/unix/kernel_version_solaris.go
@@ -77,11 +77,10 @@ var SupportSockNonblockCloexec = sync.OnceValue(func() bool {
 	}
 	if err != syscall.EPROTONOSUPPORT && err != syscall.EINVAL {
 		// Something wrong with socket(), fall back to checking the kernel version.
-		major, minor := KernelVersion()
 		if runtime.GOOS == "illumos" {
-			return major > 5 || (major == 5 && minor >= 11) // minimal requirement is SunOS 5.11
+			return KernelVersionGE(5, 11) // Minimal requirement is SunOS 5.11.
 		}
-		return major > 11 || (major == 11 && minor >= 4)
+		return KernelVersionGE(11, 4)
 	}
 	return false
 })
@@ -101,6 +100,5 @@ var SupportAccept4 = sync.OnceValue(func() bool {
 // SupportTCPKeepAliveIdleIntvlCNT determines whether the TCP_KEEPIDLE, TCP_KEEPINTVL and TCP_KEEPCNT
 // are available by checking the kernel version for Solaris 11.4.
 var SupportTCPKeepAliveIdleIntvlCNT = sync.OnceValue(func() bool {
-	major, minor := KernelVersion()
-	return major > 11 || (major == 11 && minor >= 4)
+	return KernelVersionGE(11, 4)
 })