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package ebpf
import (
"fmt"
"os"
"strings"
"sync"
)
var possibleCPU = sync.OnceValues(func() (int, error) {
return parseCPUsFromFile("/sys/devices/system/cpu/possible")
})
// PossibleCPU returns the max number of CPUs a system may possibly have
// Logical CPU numbers must be of the form 0-n
func PossibleCPU() (int, error) {
return possibleCPU()
}
// MustPossibleCPU is a helper that wraps a call to PossibleCPU and panics if
// the error is non-nil.
func MustPossibleCPU() int {
cpus, err := PossibleCPU()
if err != nil {
panic(err)
}
return cpus
}
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
}
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