From a8cc1eff4cbea011ae359404d90df04cd62b2dd0 Mon Sep 17 00:00:00 2001
From: Tim Gross <tgross@hashicorp.com>
Date: Wed, 23 Feb 2022 20:07:04 +0000
Subject: [PATCH] backport of commit 85c086e1ca24947c2856c486a5c1eb08c6fe2a92

---
 nomad/structs/csi.go | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/nomad/structs/csi.go b/nomad/structs/csi.go
index c948499e04b..9540d8445b2 100644
--- a/nomad/structs/csi.go
+++ b/nomad/structs/csi.go
@@ -411,6 +411,26 @@ func (v *CSIVolume) WriteSchedulable() bool {
 	return false
 }
 
+// HasFreeReadClaims determines if there are any free read claims available
+func (v *CSIVolume) HasFreeReadClaims() bool {
+	switch v.AccessMode {
+	case CSIVolumeAccessModeSingleNodeReader:
+		return len(v.ReadClaims) == 0
+	case CSIVolumeAccessModeSingleNodeWriter:
+		return len(v.ReadClaims) == 0 && len(v.WriteClaims) == 0
+	case CSIVolumeAccessModeUnknown:
+		// This volume was created but not yet claimed, so its
+		// capabilities have been checked in ReadSchedulable
+		return true
+	default:
+		// For multi-node AccessModes, the CSI spec doesn't allow for
+		// setting a max number of readers we track node resource
+		// exhaustion through v.ResourceExhausted which is checked in
+		// ReadSchedulable
+		return true
+	}
+}
+
 // HasFreeWriteClaims determines if there are any free write claims available
 func (v *CSIVolume) HasFreeWriteClaims() bool {
 	switch v.AccessMode {
@@ -527,6 +547,10 @@ func (v *CSIVolume) claimRead(claim *CSIVolumeClaim, alloc *Allocation) error {
 		return ErrCSIVolumeUnschedulable
 	}
 
+	if !v.HasFreeReadClaims() {
+		return ErrCSIVolumeMaxClaims
+	}
+
 	// Allocations are copy on write, so we want to keep the id but don't need the
 	// pointer. We'll get it from the db in denormalize.
 	v.ReadAllocs[claim.AllocationID] = nil