Add a function to re-read size of the loop device

Author: vojtechtrefny

docs/libblockdev-sections.txt

@@ -263,6 +263,7 @@ bd_loop_setup
 bd_loop_setup_from_fd
 bd_loop_teardown
 bd_loop_set_autoclear
+bd_loop_set_capacity
 BDLoopTech
 BDLoopTechMode
 bd_loop_is_tech_avail

src/lib/plugin_apis/loop.api

@@ -185,4 +185,18 @@ gboolean bd_loop_teardown (const gchar *loop, GError **error);
  */
 gboolean bd_loop_set_autoclear (const gchar *loop, gboolean autoclear, GError **error);
 
+/**
+ * bd_loop_set_capacity:
+ * @loop: path or name of the loop device
+ * @error: (out) (optional): place to store error (if any)
+ *
+ * Force the loop driver to reread the size of the file associated with the
+ * specified @loop device.
+ *
+ * Returns: whether the LOOP_SET_CAPACITY ioctl was successfully issued or not.
+ *
+ * Tech category: %BD_LOOP_TECH_LOOP-%BD_LOOP_TECH_MODE_MODIFY
+ */
+gboolean bd_loop_set_capacity (const gchar *loop, GError **error);
+
 #endif  /* BD_LOOP_API */

src/plugins/loop.c

@@ -517,3 +517,64 @@ gboolean bd_loop_set_autoclear (const gchar *loop, gboolean autoclear, GError **
     bd_utils_report_finished (progress_id, "Completed");
     return TRUE;
 }
+
+/**
+ * bd_loop_set_capacity:
+ * @loop: path or name of the loop device
+ * @error: (out) (optional): place to store error (if any)
+ *
+ * Force the loop driver to reread the size of the file associated with the
+ * specified @loop device.
+ *
+ * Returns: whether the LOOP_SET_CAPACITY ioctl was successfully issued or not.
+ *
+ * Tech category: %BD_LOOP_TECH_LOOP-%BD_LOOP_TECH_MODE_MODIFY
+ */
+gboolean bd_loop_set_capacity (const gchar *loop, GError **error) {
+    gchar *dev_loop = NULL;
+    gint fd = -1;
+    guint64 progress_id = 0;
+    gchar *msg = NULL;
+    guint n_try = 0;
+    gint status = 0;
+    GError *l_error = NULL;
+
+    if (!g_str_has_prefix (loop, "/dev/"))
+        dev_loop = g_strdup_printf ("/dev/%s", loop);
+
+    msg = g_strdup_printf ("Started setting up capacity on the /dev/%s device",
+                           dev_loop ? dev_loop : loop);
+    progress_id = bd_utils_report_started (msg);
+    g_free (msg);
+
+    fd = open (dev_loop ? dev_loop : loop, O_RDWR);
+    g_free (dev_loop);
+    if (fd < 0) {
+        g_set_error (&l_error, BD_LOOP_ERROR, BD_LOOP_ERROR_DEVICE,
+                     "Failed to open device %s: %m", loop);
+        bd_utils_report_finished (progress_id, l_error->message);
+        g_propagate_error (error, l_error);
+        return FALSE;
+    }
+
+    for (n_try=10, status=-1; (status != 0) && (n_try > 0); n_try--) {
+        status = ioctl (fd, LOOP_SET_CAPACITY, 0);
+        if (status < 0 && errno == EAGAIN)
+            g_usleep (100 * 1000); /* microseconds */
+        else
+            break;
+    }
+
+    if (status != 0) {
+        g_set_error (&l_error, BD_LOOP_ERROR, BD_LOOP_ERROR_FAIL,
+                     "Failed to set capacity of the device %s: %m", loop);
+        close (fd);
+        bd_utils_report_finished (progress_id, l_error->message);
+        g_propagate_error (error, l_error);
+        return FALSE;
+    }
+
+    close (fd);
+    bd_utils_report_finished (progress_id, "Completed");
+    return TRUE;
+}

src/plugins/loop.h

@@ -66,5 +66,6 @@ gboolean bd_loop_setup_from_fd (gint fd, guint64 offset, guint64 size, gboolean
 gboolean bd_loop_teardown (const gchar *loop, GError **error);
 
 gboolean bd_loop_set_autoclear (const gchar *loop, gboolean autoclear, GError **error);
+gboolean bd_loop_set_capacity (const gchar *loop, GError **error);
 
 #endif  /* BD_LOOP */

tests/loop_test.py

@@ -2,7 +2,7 @@
 import unittest
 import overrides_hack
 
-from utils import create_sparse_tempfile, TestTags, tag_test, required_plugins
+from utils import create_sparse_tempfile, create_sparse_file, TestTags, tag_test, required_plugins
 
 import gi
 gi.require_version('BlockDev', '3.0')
@@ -11,6 +11,7 @@
 
 @required_plugins(("loop",))
 class LoopTestCase(unittest.TestCase):
+    _loop_size = 100 * 1024**2
 
     requested_plugins = BlockDev.plugin_specs_from_names(("loop",))
 
@@ -23,7 +24,7 @@ def setUpClass(cls):
 
     def setUp(self):
         self.addCleanup(self._clean_up)
-        self.dev_file = create_sparse_tempfile("loop_test", 1024**3)
+        self.dev_file = create_sparse_tempfile("loop_test", self._loop_size)
         self.loop = None
 
     def _clean_up(self):
@@ -77,7 +78,7 @@ def test_loop_setup_with_offset(self):
         # should have smaller size due to the offset
         with open("/sys/block/%s/size" % self.loop, "r") as f:
             size = int(f.read()) * 512
-        self.assertEqual(size, 1024**3 - 10 * 1024 **2)
+        self.assertEqual(size, self._loop_size - 10 * 1024 **2)
 
         succ = BlockDev.loop_teardown(self.loop)
         self.assertTrue(succ)
@@ -219,3 +220,30 @@ def test_loop_get_set_autoclear(self):
         info = BlockDev.loop_info(self.loop)
         self.assertIsNotNone(info)
         self.assertFalse(info.autoclear)
+
+
+class LoopTestSetCapacity(LoopTestCase):
+    def test_loop_set_capacity(self):
+        succ, self.loop = BlockDev.loop_setup(self.dev_file)
+        self.assertTrue(succ)
+        self.assertTrue(self.loop)
+
+        with open("/sys/block/%s/size" % self.loop, "r") as f:
+            size = int(f.read()) * 512
+        self.assertEqual(size, self._loop_size)
+
+        # enlarge the backing file
+        create_sparse_file(self.dev_file, self._loop_size * 2)
+
+        # size shouldn't change without forcing re-read
+        with open("/sys/block/%s/size" % self.loop, "r") as f:
+            size = int(f.read()) * 512
+        self.assertEqual(size, self._loop_size)
+
+        succ = BlockDev.loop_set_capacity(self.loop)
+        self.assertTrue(succ)
+
+        # now the size should be updated
+        with open("/sys/block/%s/size" % self.loop, "r") as f:
+            size = int(f.read()) * 512
+        self.assertEqual(size, self._loop_size * 2)