Function NewMemoryFile

pkg/sentry/pgalloc/pgalloc.go:423–466

NewMemoryFile creates a MemoryFile backed by the given file. If NewMemoryFile succeeds, ownership of file is transferred to the returned MemoryFile.

(file *os.File, opts MemoryFileOpts)

// NewMemoryFile succeeds, ownership of file is transferred to the returned
// MemoryFile.
func NewMemoryFile(file *os.File, opts MemoryFileOpts) (*MemoryFile, error) {
	switch opts.DelayedEviction {
	case DelayedEvictionDefault:
		opts.DelayedEviction = DelayedEvictionEnabled
	case DelayedEvictionDisabled, DelayedEvictionManual:
		opts.UseHostMemcgPressure = false
	case DelayedEvictionEnabled:
		// ok
	default:
		return nil, fmt.Errorf("invalid MemoryFileOpts.DelayedEviction: %v", opts.DelayedEviction)
	}

	// Truncate the file to 0 bytes first to ensure that it's empty.
	if err := file.Truncate(0); err != nil {
		return nil, err
	}
	f := &MemoryFile{
		opts: opts,
		file: file,
	}
	f.initFields()

	if f.opts.DelayedEviction == DelayedEvictionEnabled && f.opts.UseHostMemcgPressure {
		stop, err := hostmm.NotifyCurrentMemcgPressureCallback(func() {
			f.mu.Lock()
			startedAny := f.startEvictionsLocked()
			f.mu.Unlock()
			if startedAny {
				log.Debugf("pgalloc.MemoryFile performing evictions due to memcg pressure")
			}
		}, "low")
		if err != nil {
			return nil, fmt.Errorf("failed to configure memcg pressure level notifications: %v", err)
		}
		f.stopNotifyPressure = stop
	}

	go f.releaserMain() // S/R-SAFE: f.mu

	if !opts.DisableIMAWorkAround {
		IMAWorkAroundForMemFile(file.Fd())
	}
	return f, nil
}

func (f *MemoryFile) initFields() {
	// Initially, all pages are void.