libcontainer: intelrdt: use init() to avoid race condition

[xiaochenshen]

This is the follow-up PR of #1279 to fix remaining issues:

Use init() to avoid race condition in IsIntelRdtEnabled().
Add also rename some variables and functions.

Signed-off-by: Xiaochen Shen xiaochen.shen@intel.com

[cyphar]

If we only need to do this once, why not just do it in an init and set the flag when the program starts?

[xiaochenshen]

@cyphar

Thank you for code review.

Intel RDT/CAT is a hardware-dependent feature. We wish add zero/minimal overhead to the hardware platform which doesn't support this feature. So there are several orthogonal call paths in libcontainer to check the capability:

1. In loadFactory() --> libcontainer.New().
2. In LinuxFactory.Create() and Load().
3. In ConfigValidator.Validate()
4. In libcontainer and intelrdt test cases.

Taking loadFactory() --> libcontainer.New() for example. It calls IsIntelRdtEnabled() to check the capability. If not support, libcontainer.New() will not add intelRdtManager as a factory constructor option. In subsequent container creating, running and destroying life cycle, intelRdtManager handles Intel RDT operations. If intelRdtManager is nil, we will not touch Intel RDT related functionality.

From my understanding, keeping IsIntelRdtEnabled() as a "utility" function is no harm in this case. We could check the capability in outside package without adding intelRdtManager hooks. Please correct me if I am wrong.

Thank you.

[cyphar]

I don't think you understood my question. I was asking why don't we set the isIntelRdtEnabled flag inside an init rather than setting it when you do the check (and then just making IsEnabled check that flag and not touch it). Something like

package intelrdt

// ... rest of package ...

func init() {
  // code to check if it's enabled
  isIntelRdtEnabled = true // or whatever
}

func IsEnabled() {
  return isIntelRdtEnabled
}

So you don't need to do the sync.Do stuff.

[xiaochenshen]

@cyphar

package intelrdt
func init() {

I got it. Thank you for suggestion.

[cyphar]

LGTM.

[crosbymichael]

LGTM