ulimit.go

package ulimit

var supportsFDManagement = false

// getFDLimit returns the soft and hard limits of file descriptor counts
var getFDLimit func() (int64, int64, error) 
var setFDLimit func(int64, int64) error

// maxFds is the maximum number of file descriptors that go-ipfs
// can use. The default value is 1024. This can be overwritten by the
// IPFS_FD_MAX env variable
var maxFds = uint64(1024)

// SetMaxFds sets the maxFds value from IPFS_FD_MAX
// env variable if it's present on the system
func SetMaxFds() {
	// check if the IPFS_FD_MAX is set up and if it does
	// not have a valid fds number notify the user
	if val := os.Getenv("IPFS_FD_MAX"); val != "" {

 		fds, err := strconv.ParseUint(val, 10, 64)
		if err != nil {
			log.Errorf("bad value for IPFS_FD_MAX: %s", err)
			return
		}

		maxFds = fds
	}
}

func ManageFDLimit() {
  if !supportsFDManagement {
    return // no support on this platform, maybe log a message?
  }
  SetMaxFds()

  // Same logic you currently have in ManageFD, just using the generalized functions defined above
}

ulimit_freebsd.go

// +build freebsd

package ulimit

func init() {
  supportsFDManagement = true
  getFDLimit = freebsdGetFDLimit
  setFDLimit = freebsdSetFDLimit
}

func freebsdGetFDLimit() (int64, int64, error) {
  ...
}

func freebsdSetFDLimit(int64, int64) error {
  ...
}

ulimit_unix.go

// +build darwin linux netbsd openbsd

package ulimit

func init() {
  supportsFDManagement = true
  getFDLimit = getFDLimit
  setFDLimit = setFDLimit
}

func getFDLimit() (int64, int64, error) {
  ...
}

func setFDLimit(int64, int64) error {
  ...
}