pkg/spec.InitFSMounts: optimize

Instead of getting mount options from /proc/self/mountinfo, which is
very costly to read/parse (and can even be unreliable), let's use
statfs(2) to figure out the flags we need.

[v2: move getting default options to pkg/util, make it linux-specific]

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

3 files changed, 43 insertions, 11 deletions

diff --git a/pkg/util/mountOpts.go b/pkg/util/mountOpts.go
index d21800bc3..329a7c913 100644
--- a/pkg/util/mountOpts.go
+++ b/pkg/util/mountOpts.go
@@ -13,19 +13,17 @@ var (
 	ErrDupeMntOption = errors.Errorf("duplicate mount option passed")
 )
 
-// DefaultMountOptions sets default mount options for ProcessOptions.
-type DefaultMountOptions struct {
-	Noexec bool
-	Nosuid bool
-	Nodev  bool
+type defaultMountOptions struct {
+	noexec bool
+	nosuid bool
+	nodev  bool
 }
 
 // ProcessOptions parses the options for a bind or tmpfs mount and ensures that
 // they are sensible and follow convention. The isTmpfs variable controls
 // whether extra, tmpfs-specific options will be allowed.
-// The defaults variable controls default mount options that will be set. If it
-// is not included, they will be set unconditionally.
-func ProcessOptions(options []string, isTmpfs bool, defaults *DefaultMountOptions) ([]string, error) {
+// The sourcePath variable, if not empty, contains a bind mount source.
+func ProcessOptions(options []string, isTmpfs bool, sourcePath string) ([]string, error) {
 	var (
 		foundWrite, foundSize, foundProp, foundMode, foundExec, foundSuid, foundDev, foundCopyUp, foundBind, foundZ bool
 	)
@@ -122,13 +120,17 @@ func ProcessOptions(options []string, isTmpfs bool, defaults *DefaultMountOption
 	if !foundProp {
 		newOptions = append(newOptions, "rprivate")
 	}
-	if !foundExec && (defaults == nil || defaults.Noexec) {
+	defaults, err := getDefaultMountOptions(sourcePath)
+	if err != nil {
+		return nil, err
+	}
+	if !foundExec && defaults.noexec {
 		newOptions = append(newOptions, "noexec")
 	}
-	if !foundSuid && (defaults == nil || defaults.Nosuid) {
+	if !foundSuid && defaults.nosuid {
 		newOptions = append(newOptions, "nosuid")
 	}
-	if !foundDev && (defaults == nil || defaults.Nodev) {
+	if !foundDev && defaults.nodev {
 		newOptions = append(newOptions, "nodev")
 	}
 	if isTmpfs && !foundCopyUp {
diff --git a/pkg/util/mountOpts_linux.go b/pkg/util/mountOpts_linux.go
new file mode 100644
index 000000000..3eac4dd25
--- /dev/null
+++ b/pkg/util/mountOpts_linux.go
@@ -0,0 +1,23 @@
+package util
+
+import (
+	"os"
+
+	"golang.org/x/sys/unix"
+)
+
+func getDefaultMountOptions(path string) (defaultMountOptions, error) {
+	opts := defaultMountOptions{true, true, true}
+	if path == "" {
+		return opts, nil
+	}
+	var statfs unix.Statfs_t
+	if e := unix.Statfs(path, &statfs); e != nil {
+		return opts, &os.PathError{Op: "statfs", Path: path, Err: e}
+	}
+	opts.nodev = (statfs.Flags&unix.MS_NODEV == unix.MS_NODEV)
+	opts.noexec = (statfs.Flags&unix.MS_NOEXEC == unix.MS_NOEXEC)
+	opts.nosuid = (statfs.Flags&unix.MS_NOSUID == unix.MS_NOSUID)
+
+	return opts, nil
+}
diff --git a/pkg/util/mountOpts_other.go b/pkg/util/mountOpts_other.go
new file mode 100644
index 000000000..6a34942e5
--- /dev/null
+++ b/pkg/util/mountOpts_other.go
@@ -0,0 +1,7 @@
+// +build !linux
+
+package util
+
+func getDefaultMountOptions(path string) (opts defaultMountOptions, err error) {
+	return
+}