whatcanGOwrong

go/pkg/mod/github.com/cilium/ebpf@v0.11.0/internal/cpu.go

@@ -0,0 +1,51 @@
+package internal
+
+import (
+	"fmt"
+	"os"
+	"strings"
+)
+
+// PossibleCPUs returns the max number of CPUs a system may possibly have
+// Logical CPU numbers must be of the form 0-n
+var PossibleCPUs = Memoize(func() (int, error) {
+	return parseCPUsFromFile("/sys/devices/system/cpu/possible")
+})
+
+func parseCPUsFromFile(path string) (int, error) {
+	spec, err := os.ReadFile(path)
+	if err != nil {
+		return 0, err
+	}
+
+	n, err := parseCPUs(string(spec))
+	if err != nil {
+		return 0, fmt.Errorf("can't parse %s: %v", path, err)
+	}
+
+	return n, nil
+}
+
+// parseCPUs parses the number of cpus from a string produced
+// by bitmap_list_string() in the Linux kernel.
+// Multiple ranges are rejected, since they can't be unified
+// into a single number.
+// This is the format of /sys/devices/system/cpu/possible, it
+// is not suitable for /sys/devices/system/cpu/online, etc.
+func parseCPUs(spec string) (int, error) {
+	if strings.Trim(spec, "\n") == "0" {
+		return 1, nil
+	}
+
+	var low, high int
+	n, err := fmt.Sscanf(spec, "%d-%d\n", &low, &high)
+	if n != 2 || err != nil {
+		return 0, fmt.Errorf("invalid format: %s", spec)
+	}
+	if low != 0 {
+		return 0, fmt.Errorf("CPU spec doesn't start at zero: %s", spec)
+	}
+
+	// cpus is 0 indexed
+	return high + 1, nil
+}