[lxc-devel] [lxd/master] lxd/util: Detect hugetlbfs mount point

[stgraber on Github]

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From 571caeb86d7b4aabee84ebc1fb83e610b4e07031 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?St=C3=A9phane=20Graber?= <stgraber at ubuntu.com>
Date: Sun, 28 Jun 2020 23:22:13 -0400
Subject: [PATCH] lxd/util: Detect hugetlbfs mount point
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Closes #7593

Signed-off-by: Stéphane Graber <stgraber at ubuntu.com>
---
 lxd/instance/drivers/driver_qemu.go |  8 ++++++-
 lxd/util/kernel.go                  | 35 +++++++++++++++++++++++++++++
 2 files changed, 42 insertions(+), 1 deletion(-)

diff --git a/lxd/instance/drivers/driver_qemu.go b/lxd/instance/drivers/driver_qemu.go
index 471100f64a..7617db6da1 100644
--- a/lxd/instance/drivers/driver_qemu.go
+++ b/lxd/instance/drivers/driver_qemu.go
@@ -775,7 +775,13 @@ func (vm *qemu) Start(stateful bool) error {
 	}
 
 	if shared.IsTrue(vm.expandedConfig["limits.memory.hugepages"]) {
-		qemuCmd = append(qemuCmd, "-mem-path", "/dev/hugepages/", "-mem-prealloc")
+		hugetlb, err := util.HugepagesPath()
+		if err != nil {
+			op.Done(err)
+			return err
+		}
+
+		qemuCmd = append(qemuCmd, "-mem-path", hugetlb, "-mem-prealloc")
 	}
 
 	if vm.expandedConfig["raw.qemu"] != "" {
diff --git a/lxd/util/kernel.go b/lxd/util/kernel.go
index 0272dd101e..4019477af7 100644
--- a/lxd/util/kernel.go
+++ b/lxd/util/kernel.go
@@ -42,3 +42,38 @@ func HasFilesystem(filesystem string) bool {
 
 	return false
 }
+
+// HugepagesPath attempts to locate the mount point of the hugepages filesystem.
+func HugepagesPath() (string, error) {
+	// Find the source mount of the path
+	file, err := os.Open("/proc/mounts")
+	if err != nil {
+		return "", err
+	}
+	defer file.Close()
+
+	scanner := bufio.NewScanner(file)
+	matches := []string{}
+	for scanner.Scan() {
+		line := scanner.Text()
+		cols := strings.Fields(line)
+
+		if cols[2] == "hugetlbfs" {
+			matches = append(matches, cols[1])
+		}
+	}
+
+	if len(matches) == 0 {
+		return "", fmt.Errorf("No hugetlbfs mount found, can't use hugepages")
+	}
+
+	if len(matches) > 1 {
+		if shared.StringInSlice("/dev/hugepages", matches) {
+			return "/dev/hugepages", nil
+		}
+
+		return "", fmt.Errorf("More than one hugetlbfs instance found and none at standard /dev/hugepages")
+	}
+
+	return matches[0], nil
+}