sysinfo: Ignore "hidden" sysfs device entries

Some devices are "hidden" from userspace due to various
reasons. One reason is native nvme multipathing, where the
path devices do not present a device node to the user but
only exposes the stacking device as the only nvme device.
Still there are sysfs attributes for these hidden devices, but
we should ignore them altogether because these are not "real"
devices at all.

Signed-off-by: Sagi Grimberg <sagi@grimberg.me>

utils/sysfs/fakesysfs/fake.go

@@ -128,6 +128,10 @@ func (fs *FakeSysFs) GetBlockDeviceNumbers(name string) (string, error) {
 	return "8:0\n", nil
 }
 
+func (fs *FakeSysFs) IsBlockDeviceHidden(name string) (bool, error) {
+	return false, nil
+}
+
 func (fs *FakeSysFs) GetNetworkDevices() ([]os.FileInfo, error) {
 	return []os.FileInfo{&fs.info}, nil
 }

utils/sysfs/sysfs.go

@@ -101,6 +101,9 @@ type SysFs interface {
 	GetBlockDeviceScheduler(string) (string, error)
 	// Get device major:minor number string.
 	GetBlockDeviceNumbers(string) (string, error)
+	// Is the device "hidden" (meaning will not have a device handle)
+	// This is the case with native nvme multipathing.
+	IsBlockDeviceHidden(string) (bool, error)
 
 	GetNetworkDevices() ([]os.FileInfo, error)
 	GetNetworkAddress(string) (string, error)
@@ -212,6 +215,26 @@ func (fs *realSysFs) GetBlockDeviceNumbers(name string) (string, error) {
 	return string(dev), nil
 }
 
+func (fs *realSysFs) IsBlockDeviceHidden(name string) (bool, error) {
+	// See: https://www.kernel.org/doc/Documentation/ABI/stable/sysfs-block
+	//      https://git.kernel.org/pub/scm/utils/util-linux/util-linux.git
+	//        - c8487d854ba5 ("lsblk: Ignore hidden devices")
+	devHiddenPath := path.Join(blockDir, name, "/hidden")
+	hidden, err := os.ReadFile(devHiddenPath)
+	if err != nil && os.IsNotExist(err) {
+		// older OS may not have /hidden sysfs entry, so for sure
+		// it is not a hidden device...
+		return false, nil
+	}
+	if err != nil {
+		return false, fmt.Errorf("failed to read %s: %s", devHiddenPath, err)
+	}
+	if string(hidden) == "1" {
+		return true, nil
+	}
+	return false, nil
+}
+
 func (fs *realSysFs) GetBlockDeviceScheduler(name string) (string, error) {
 	sched, err := os.ReadFile(path.Join(blockDir, name, "/queue/scheduler"))
 	if err != nil {

utils/sysinfo/sysinfo.go

@@ -57,6 +57,16 @@ func GetBlockDeviceInfo(sysfs sysfs.SysFs) (map[string]info.DiskInfo, error) {
 		if strings.HasPrefix(name, "loop") || strings.HasPrefix(name, "ram") || strings.HasPrefix(name, "sr") {
 			continue
 		}
+		// Ignore "hidden" devices (i.e. nvme path device sysfs entries).
+		// These devices are in the form of /dev/nvme$Xc$Yn$Z and will
+		// not have a device handle (i.e. "hidden")
+		isHidden, err := sysfs.IsBlockDeviceHidden(name)
+		if err != nil {
+			return nil, err
+		}
+		if isHidden {
+			continue
+		}
 		diskInfo := info.DiskInfo{
 			Name: name,
 		}