cephfs: add kernel version detection for mounting with client

Linux kernel 4.17.0 adds support for quota with CephFS. Without quota,
it is not possible to fullfill the requirements of the CSI Spec and
guarantee sufficient space on the filesystem for a volume. With this in
mind, usage of the kernel client is only allowed with kernel 4.17.0 or
newer.

However, some Linux vendors backport features and patches to their
Enterprise products. These kernels may have an older version, but do
support quota. One of these is the kernel that comes with RHEL-7.7.

By comparing the current running version of the Linux kernel against
known versions that support quota, we can now automatically decide to
use the kernel client, or not.

Note that this does not change the 'forcekernelclient' parameter. The
parameter is still available and can be used for kernels that are not in
the 'known to support quota list'. Or users can pass the parameter to
use a CephFS kernel client that does not support quota.

Signed-off-by: Niels de Vos <ndevos@redhat.com>
Signed-off-by: Madhu Rajanna <madhupr007@gmail.com>

Gopkg.lock

@@ -1366,6 +1366,7 @@
     "github.com/pkg/errors",
     "github.com/prometheus/client_golang/prometheus",
     "github.com/prometheus/client_golang/prometheus/promhttp",
+    "golang.org/x/sys/unix",
     "google.golang.org/grpc",
     "google.golang.org/grpc/codes",
     "google.golang.org/grpc/status",

pkg/cephfs/volumemounter.go

@@ -29,6 +29,7 @@ import (
 
 	"github.com/ceph/ceph-csi/pkg/util"
 
+	"golang.org/x/sys/unix"
 	"k8s.io/klog"
 )
 
@@ -47,6 +48,95 @@ var (
 	fusePidRx = regexp.MustCompile(`(?m)^ceph-fuse\[(.+)\]: starting fuse$`)
 )
 
+// Version checking the running kernel and comparing it to known versions that
+// have support for quota. Distributors of enterprise Linux have backported
+// quota support to previous versions. This function checks if the running
+// kernel is one of the versions that have the feature/fixes backported.
+//
+// `uname -r` (or Uname().Utsname.Release has a format like 1.2.3-rc.vendor
+// This can be slit up in the following components:
+// - version (1)
+// - patchlevel (2)
+// - sublevel (3) - optional, defaults to 0
+// - extraversion (rc) - optional, matching integers only
+// - distribution (.vendor) - optional, match against whole `uname -r` string
+//
+// For matching multiple versions, the kernelSupport type contains a backport
+// bool, which will cause matching
+// version+patchlevel+sublevel+(>=extraversion)+(~distribution)
+//
+// In case the backport bool is false, a simple check for higher versions than
+// version+patchlevel+sublevel is done.
+func kernelSupportsQuota(release string) bool {
+	type kernelSupport struct {
+		version      int
+		patchlevel   int
+		sublevel     int
+		extraversion int    // prefix of the part after the first "-"
+		distribution string // component of full extraversion
+		backport     bool   // backports have a fixed version/patchlevel/sublevel
+	}
+
+	quotaSupport := []kernelSupport{
+		{4, 17, 0, 0, "", false},       // standard 4.17+ versions
+		{3, 10, 0, 1062, ".el7", true}, // RHEL-7.7
+	}
+
+	vers := strings.Split(strings.SplitN(release, "-", 2)[0], ".")
+	version, err := strconv.Atoi(vers[0])
+	if err != nil {
+		klog.Errorf("failed to parse version from %s: %v", release, err)
+		return false
+	}
+	patchlevel, err := strconv.Atoi(vers[1])
+	if err != nil {
+		klog.Errorf("failed to parse patchlevel from %s: %v", release, err)
+		return false
+	}
+	sublevel := 0
+	if len(vers) >= 3 {
+		sublevel, err = strconv.Atoi(vers[2])
+		if err != nil {
+			klog.Errorf("failed to parse sublevel from %s: %v", release, err)
+			return false
+		}
+	}
+	extra := strings.SplitN(release, "-", 2)
+	extraversion := 0
+	if len(extra) == 2 {
+		// ignore errors, 1st component of extraversion does not need to be an int
+		extraversion, err = strconv.Atoi(strings.Split(extra[1], ".")[0])
+		if err != nil {
+			// "go lint" wants err to be checked...
+			extraversion = 0
+		}
+	}
+
+	// compare running kernel against known versions
+	for _, kernel := range quotaSupport {
+		if !kernel.backport {
+			// deal with the default case(s), find >= match for version, patchlevel, sublevel
+			if version > kernel.version || (version == kernel.version && patchlevel > kernel.patchlevel) ||
+				(version == kernel.version && patchlevel == kernel.patchlevel && sublevel >= kernel.sublevel) {
+				return true
+			}
+		} else {
+			// specific backport, match distribution initially
+			if !strings.Contains(release, kernel.distribution) {
+				continue
+			}
+
+			// strict match version, patchlevel, sublevel, and >= match extraversion
+			if version == kernel.version && patchlevel == kernel.patchlevel &&
+				sublevel == kernel.sublevel && extraversion >= kernel.extraversion {
+				return true
+			}
+		}
+	}
+	klog.Errorf("kernel %s does not support quota", release)
+	return false
+}
+
 // Load available ceph mounters installed on system into availableMounters
 // Called from driver.go's Run()
 func loadAvailableMounters(conf *util.Config) error {
@@ -57,21 +147,15 @@ func loadAvailableMounters(conf *util.Config) error {
 
 	err := kernelMounterProbe.Run()
 	if err == nil {
-		kernelVersion, _, err := execCommand(context.TODO(), "uname", "-r")
-		if err != nil {
-			return err
-		}
-		vers := strings.Split(string(kernelVersion), ".")
-		majorVers, err := strconv.Atoi(vers[0])
-		if err != nil {
-			return err
-		}
-		minorVers, err := strconv.Atoi(vers[1])
+		// fetch the current running kernel info
+		utsname := unix.Utsname{}
+		err := unix.Uname(&utsname)
 		if err != nil {
 			return err
 		}
+		release := string(utsname.Release[:64])
 
-		if conf.ForceKernelCephFS || majorVers > 4 || (majorVers >= 4 && minorVers >= 17) {
+		if conf.ForceKernelCephFS || kernelSupportsQuota(release) {
 			klog.Infof("loaded mounter: %s", volumeMounterKernel)
 			availableMounters = append(availableMounters, volumeMounterKernel)
 		} else {

pkg/cephfs/volumemounter_test.go

@@ -0,0 +1,56 @@
+/*
+Copyright 2019 The Ceph-CSI Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package cephfs
+
+import (
+	"testing"
+)
+
+func init() {
+}
+
+func TestKernelSupportsQuota(t *testing.T) {
+	supportsQuota := []string{
+		"4.17.0",
+		"5.0.0",
+		"4.17.0-rc1",
+		"4.18.0-80.el8",
+		"3.10.0-1062.el7.x86_64",     // 1st backport
+		"3.10.0-1062.4.1.el7.x86_64", // updated backport
+	}
+
+	noQuota := []string{
+		"2.6.32-754.15.3.el6.x86_64", // too old
+		"3.10.0-123.el7.x86_64",      // too old for backport
+		"3.10.0-1062.4.1.el8.x86_64", // nonexisting RHEL-8 kernel
+		"3.11.0-123.el7.x86_64",      // nonexisting RHEL-7 kernel
+	}
+
+	for _, kernel := range supportsQuota {
+		ok := kernelSupportsQuota(kernel)
+		if !ok {
+			t.Errorf("support expected for %s", kernel)
+		}
+	}
+
+	for _, kernel := range noQuota {
+		ok := kernelSupportsQuota(kernel)
+		if ok {
+			t.Errorf("no support expected for %s", kernel)
+		}
+	}
+}