mount: replace mountinfo handling with moby/sys/mountinfo

Trying to reduce duplicated effort in maintaining a mountinfo
parser, this patch replaces the local implementation with the
implementation in github.com/moby/sys, which is actively maintained
and contains various optimizations.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

vendor/github.com/moby/sys/mountinfo/mountinfo_bsd.go

@@ -0,0 +1,67 @@
+// +build freebsd,cgo openbsd,cgo
+
+package mountinfo
+
+/*
+#include <sys/param.h>
+#include <sys/ucred.h>
+#include <sys/mount.h>
+*/
+import "C"
+
+import (
+	"fmt"
+	"reflect"
+	"unsafe"
+)
+
+// parseMountTable returns information about mounted filesystems
+func parseMountTable(filter FilterFunc) ([]*Info, error) {
+	var rawEntries *C.struct_statfs
+
+	count := int(C.getmntinfo(&rawEntries, C.MNT_WAIT))
+	if count == 0 {
+		return nil, fmt.Errorf("Failed to call getmntinfo")
+	}
+
+	var entries []C.struct_statfs
+	header := (*reflect.SliceHeader)(unsafe.Pointer(&entries))
+	header.Cap = count
+	header.Len = count
+	header.Data = uintptr(unsafe.Pointer(rawEntries))
+
+	var out []*Info
+	for _, entry := range entries {
+		var mountinfo Info
+		var skip, stop bool
+		mountinfo.Mountpoint = C.GoString(&entry.f_mntonname[0])
+		mountinfo.FSType = C.GoString(&entry.f_fstypename[0])
+		mountinfo.Source = C.GoString(&entry.f_mntfromname[0])
+
+		if filter != nil {
+			// filter out entries we're not interested in
+			skip, stop = filter(&mountinfo)
+			if skip {
+				continue
+			}
+		}
+
+		out = append(out, &mountinfo)
+		if stop {
+			break
+		}
+	}
+	return out, nil
+}
+
+func mounted(path string) (bool, error) {
+	// Fast path: compare st.st_dev fields.
+	// This should always work for FreeBSD and OpenBSD.
+	mounted, err := mountedByStat(path)
+	if err == nil {
+		return mounted, nil
+	}
+
+	// Fallback to parsing mountinfo
+	return mountedByMountinfo(path)
+}