blockdev-util: add fd-based flavour of get_block_device()

src/shared/blockdev-util.c

@@ -57,21 +57,16 @@ int block_get_whole_disk(dev_t d, dev_t *ret) {
         return 1;
 }
 
-int get_block_device(const char *path, dev_t *ret) {
-        _cleanup_close_ int fd = -1;
+int get_block_device_fd(int fd, dev_t *ret) {
         struct stat st;
         int r;
 
-        assert(path);
+        assert(fd >= 0);
         assert(ret);
 
         /* Gets the block device directly backing a file system. If the block device is encrypted, returns
          * the device mapper block device. */
 
-        fd = open(path, O_RDONLY|O_NOFOLLOW|O_CLOEXEC);
-        if (fd < 0)
-                return -errno;
-
         if (fstat(fd, &st))
                 return -errno;
 
@@ -90,6 +85,19 @@ int get_block_device(const char *path, dev_t *ret) {
         return 0;
 }
 
+int get_block_device(const char *path, dev_t *ret) {
+        _cleanup_close_ int fd = -1;
+
+        assert(path);
+        assert(ret);
+
+        fd = open(path, O_RDONLY|O_NOFOLLOW|O_CLOEXEC);
+        if (fd < 0)
+                return -errno;
+
+        return get_block_device_fd(fd, ret);
+}
+
 int block_get_originating(dev_t dt, dev_t *ret) {
         _cleanup_closedir_ DIR *d = NULL;
         _cleanup_free_ char *t = NULL;

src/shared/blockdev-util.h

@@ -15,6 +15,7 @@
 int block_get_whole_disk(dev_t d, dev_t *ret);
 int block_get_originating(dev_t d, dev_t *ret);
 
+int get_block_device_fd(int fd, dev_t *ret);
 int get_block_device(const char *path, dev_t *dev);
 
 int get_block_device_harder(const char *path, dev_t *dev);