Relax restrictions on filesystem size reporting

Apparently some filesystems such as ZFS and occasionally NTFS can report
filesystem usages that are negative, or above the maximum total size of
the filesystem. This relaxes the constraints on `DiskUsage` so that an
exception is not thrown.

If 0 is passed as the totalBytes, `.getFreeDiskAsPercentage()` will
always return 100.0% free (to ensure the disk threshold decider fails
open)

Fixes elastic#9249
Relates to elastic#9260

src/main/java/org/elasticsearch/cluster/DiskUsage.java

@@ -31,20 +31,32 @@ public class DiskUsage {
     final long totalBytes;
     final long freeBytes;
 
+    /**
+     * Create a new DiskUsage, if {@code totalBytes} is 0, {@get getFreeDiskAsPercentage}
+     * will always return 100.0% free
+     */
     public DiskUsage(String nodeId, String nodeName, long totalBytes, long freeBytes) {
-        if ((totalBytes < freeBytes) || (totalBytes < 0)) {
-            throw new IllegalStateException("Free bytes [" + freeBytes +
-                    "] cannot be less than 0 or greater than total bytes [" + totalBytes + "]");
-        }
         this.nodeId = nodeId;
         this.nodeName = nodeName;
-        this.totalBytes = totalBytes;
         this.freeBytes = freeBytes;
+        this.totalBytes = totalBytes;
+    }
+
+    public String getNodeId() {
+        return nodeId;
+    }
+
+    public String getNodeName() {
+        return nodeName;
     }
 
     public double getFreeDiskAsPercentage() {
-        double freePct = 100.0 * ((double)freeBytes / totalBytes);
-        return freePct;
+        // We return 100.0% in order to fail "open", in that if we have invalid
+        // numbers for the total bytes, it's as if we don't know disk usage.
+        if (totalBytes == 0) {
+            return 100.0;
+        }
+        return 100.0 * ((double)freeBytes / totalBytes);
     }
 
     public long getFreeBytes() {

src/main/java/org/elasticsearch/cluster/routing/allocation/decider/DiskThresholdDecider.java

@@ -519,6 +519,9 @@ public Decision canRemain(ShardRouting shardRouting, RoutingNode node, RoutingAl
      * @return DiskUsage representing given node using the average disk usage
      */
     public DiskUsage averageUsage(RoutingNode node, Map<String, DiskUsage> usages) {
+        if (usages.size() == 0) {
+            return new DiskUsage(node.nodeId(), node.node().name(), 0, 0);
+        }
         long totalBytes = 0;
         long freeBytes = 0;
         for (DiskUsage du : usages.values()) {
@@ -537,7 +540,9 @@ public DiskUsage averageUsage(RoutingNode node, Map<String, DiskUsage> usages) {
      */
     public double freeDiskPercentageAfterShardAssigned(DiskUsage usage, Long shardSize) {
         shardSize = (shardSize == null) ? 0 : shardSize;
-        return 100.0 - (((double)(usage.getUsedBytes() + shardSize) / usage.getTotalBytes()) * 100.0);
+        DiskUsage newUsage = new DiskUsage(usage.getNodeId(), usage.getNodeName(),
+                usage.getTotalBytes(), usage.getFreeBytes() - shardSize);
+        return newUsage.getFreeDiskAsPercentage();
     }
 
     /**

src/test/java/org/elasticsearch/cluster/DiskUsageTests.java

@@ -34,6 +34,25 @@ public void diskUsageCalcTest() {
         assertThat(du.getUsedBytes(), equalTo(60L));
         assertThat(du.getTotalBytes(), equalTo(100L));
 
+        // Test that DiskUsage handles invalid numbers, as reported by some
+        // filesystems (ZFS & NTFS)
+        DiskUsage du2 = new DiskUsage("node1", "n1", 100, 101);
+        assertThat(du2.getFreeDiskAsPercentage(), equalTo(101.0));
+        assertThat(du2.getFreeBytes(), equalTo(101L));
+        assertThat(du2.getUsedBytes(), equalTo(-1L));
+        assertThat(du2.getTotalBytes(), equalTo(100L));
+
+        DiskUsage du3 = new DiskUsage("node1", "n1", -1, -1);
+        assertThat(du3.getFreeDiskAsPercentage(), equalTo(100.0));
+        assertThat(du3.getFreeBytes(), equalTo(-1L));
+        assertThat(du3.getUsedBytes(), equalTo(0L));
+        assertThat(du3.getTotalBytes(), equalTo(-1L));
+
+        DiskUsage du4 = new DiskUsage("node1", "n1", 0, 0);
+        assertThat(du4.getFreeDiskAsPercentage(), equalTo(100.0));
+        assertThat(du4.getFreeBytes(), equalTo(0L));
+        assertThat(du4.getUsedBytes(), equalTo(0L));
+        assertThat(du4.getTotalBytes(), equalTo(0L));
     }
 
     @Test
@@ -42,18 +61,17 @@ public void randomDiskUsageTest() {
         for (int i = 1; i < iters; i++) {
             long total = between(Integer.MIN_VALUE, Integer.MAX_VALUE);
             long free = between(Integer.MIN_VALUE, Integer.MAX_VALUE);
-            if (free > total || total <= 0) {
-                try {
-                    new DiskUsage("random", "random", total, free);
-                    fail("should never reach this");
-                } catch (IllegalStateException e) {
-                }
+            DiskUsage du = new DiskUsage("random", "random", total, free);
+            if (total == 0) {
+                assertThat(du.getFreeBytes(), equalTo(free));
+                assertThat(du.getTotalBytes(), equalTo(0L));
+                assertThat(du.getUsedBytes(), equalTo(-free));
+                assertThat(du.getFreeDiskAsPercentage(), equalTo(100.0));
             } else {
-                DiskUsage du = new DiskUsage("random", "random", total, free);
                 assertThat(du.getFreeBytes(), equalTo(free));
                 assertThat(du.getTotalBytes(), equalTo(total));
                 assertThat(du.getUsedBytes(), equalTo(total - free));
-                assertThat(du.getFreeDiskAsPercentage(), equalTo(100.0 * ((double)free / total)));
+                assertThat(du.getFreeDiskAsPercentage(), equalTo(100.0 * ((double) free / total)));
             }
         }
     }