From 584181f8e7015e8fbd319be9a5a9341d8f3d64df Mon Sep 17 00:00:00 2001
From: Steven Kreuzer <skreuzer@FreeBSD.org>
Date: Fri, 13 Dec 2019 22:15:45 -0500
Subject: [PATCH] Expose xs_qm_dquot_unused XFS counter

Add support for exposing the xs_qm_dquot_unused XFS statistic which appears in
Linux 4.20 and later.

Signed-off-by: Steven Kreuzer <skreuzer@FreeBSD.org>
---
 xfs/parse.go      | 18 ++++++++++++++----
 xfs/parse_test.go | 22 ++++++++++++++++++++++
 xfs/xfs.go        |  1 +
 3 files changed, 37 insertions(+), 4 deletions(-)

diff --git a/xfs/parse.go b/xfs/parse.go
index f3f30d7c9..ba3afea3e 100644
--- a/xfs/parse.go
+++ b/xfs/parse.go
@@ -381,11 +381,15 @@ func extendedPrecisionStats(us []uint64) (ExtendedPrecisionStats, error) {
 }
 
 func quotaManagerStats(us []uint32) (QuotaManagerStats, error) {
-	if l := len(us); l < 8 {
-		return QuotaManagerStats{}, fmt.Errorf("insufficient number of values for XFS quota stats expecting at least 8, got: %d", l)
+	// The "Unused" attribute first appears in Linux 4.20
+	// As a result either 8 or 9 elements may appear in this slice depending on
+	// the kernel version.
+	l := len(us)
+	if l != 8 && l != 9 {
+		return QuotaManagerStats{}, fmt.Errorf("incorrect number of values for XFS quota stats: %d", l)
 	}
 
-	return QuotaManagerStats{
+	s := QuotaManagerStats{
 		Reclaims:      us[0],
 		ReclaimMisses: us[1],
 		DquoteDups:    us[2],
@@ -394,7 +398,13 @@ func quotaManagerStats(us []uint32) (QuotaManagerStats, error) {
 		Wants:         us[5],
 		ShakeReclaims: us[6],
 		InactReclaims: us[7],
-	}, nil
+	}
+
+	if l > 8 {
+		s.Unused = us[8]
+	}
+
+	return s, nil
 }
 
 func debugStats(us []uint32) (DebugStats, error) {
diff --git a/xfs/parse_test.go b/xfs/parse_test.go
index 1774665af..b799f4b2c 100644
--- a/xfs/parse_test.go
+++ b/xfs/parse_test.go
@@ -368,6 +368,11 @@ func TestParseStats(t *testing.T) {
 			s:       "qm 1 2 3 4 5 6 7",
 			invalid: true,
 		},
+		{
+			name:    "qm bad",
+			s:       "qm 1 2 3 4 5 6 7 8 9 10",
+			invalid: true,
+		},
 		{
 			name: "qm OK",
 			s:    "qm 1 2 3 4 5 6 7 8",
@@ -384,6 +389,23 @@ func TestParseStats(t *testing.T) {
 				},
 			},
 		},
+		{
+			name: "qm OK",
+			s:    "qm 1 2 3 4 5 6 7 8 9",
+			stats: &xfs.Stats{
+				QuotaManager: xfs.QuotaManagerStats{
+					Reclaims:      1,
+					ReclaimMisses: 2,
+					DquoteDups:    3,
+					CacheMisses:   4,
+					CacheHits:     5,
+					Wants:         6,
+					ShakeReclaims: 7,
+					InactReclaims: 8,
+					Unused:        9,
+				},
+			},
+		},
 		{
 			name:    "abtb2 bad",
 			s:       "abtb2 1 2 3 4 5 6",
diff --git a/xfs/xfs.go b/xfs/xfs.go
index 018a0b89c..cc8b36bed 100644
--- a/xfs/xfs.go
+++ b/xfs/xfs.go
@@ -202,6 +202,7 @@ type QuotaManagerStats struct {
 	Wants         uint32
 	ShakeReclaims uint32
 	InactReclaims uint32
+	Unused        uint32
 }
 
 // XstratStats contains statistics regarding bytes processed by the XFS daemon.