loop-util: add api for locking the block device with flock()

src/shared/loop-util.c

@@ -3,6 +3,7 @@
 #include <errno.h>
 #include <fcntl.h>
 #include <linux/loop.h>
+#include <sys/file.h>
 #include <sys/ioctl.h>
 
 #include "alloc-util.h"
@@ -233,3 +234,15 @@ int loop_device_refresh_size(LoopDevice *d, uint64_t offset, uint64_t size) {
 
         return 0;
 }
+
+int loop_device_flock(LoopDevice *d, int operation) {
+        assert(d);
+
+        if (d->fd < 0)
+                return -EBADF;
+
+        if (flock(d->fd, operation) < 0)
+                return -errno;
+
+        return 0;
+}

src/shared/loop-util.h

@@ -28,3 +28,5 @@ DEFINE_TRIVIAL_CLEANUP_FUNC(LoopDevice*, loop_device_unref);
 void loop_device_relinquish(LoopDevice *d);
 
 int loop_device_refresh_size(LoopDevice *d, uint64_t offset, uint64_t size);
+
+int loop_device_flock(LoopDevice *d, int operation);