posix: Disk free verification should have relaxed handling of inodes. (#2431)

Some filesystems do not implement a way to provide total inodes available, instead inodes
are allocated based on available disk space. For example CephFS, StoreNext CVSFS, AzureFile
driver. Allow for the available disk to be separately validate and we will validate inodes
only if the total inodes are provided by the underlying filesystem.

Fixes #2364

posix.go

@@ -143,11 +143,21 @@ func checkDiskFree(diskPath string, minFreeDisk int64) (err error) {
 	// Remove 5% from total space for cumulative disk
 	// space used for journalling, inodes etc.
 	availableDiskSpace := (float64(di.Free) / (float64(di.Total) - (0.05 * float64(di.Total)))) * 100
-	availableFiles := (float64(di.Ffree) / (float64(di.Files) - (0.05 * float64(di.Files)))) * 100
-	if int64(availableDiskSpace) <= minFreeDisk || int64(availableFiles) <= minFreeDisk {
+	if int64(availableDiskSpace) <= minFreeDisk {
 		return errDiskFull
 	}
 
+	// Some filesystems do not implement a way to provide total inodes available, instead inodes
+	// are allocated based on available disk space. For example CephFS, StoreNext CVFS, AzureFile driver.
+	// Allow for the available disk to be separately validate and we will validate inodes only if
+	// total inodes are provided by the underlying filesystem.
+	if di.Files != 0 {
+		availableFiles := (float64(di.Ffree) / (float64(di.Files) - (0.05 * float64(di.Files)))) * 100
+		if int64(availableFiles) <= minFreeDisk {
+			return errDiskFull
+		}
+	}
+
 	// Success.
 	return nil
 }