utils: rm_offset_get_from_fd: Don't combine separate extents

rmlint previously ignored holes between physically adjacent extents.
This could cause files to be detected as reflinked that weren't, if one
file had a complete extent and the other file had two pieces of it
separated by a hole.

Check for logical gaps as well as physical gaps to fix this problem.

Fixes sahib#530

lib/utilities.c

@@ -1024,9 +1024,9 @@ RmOff rm_offset_get_from_fd(int fd, RmOff file_offset, RmOff *file_offset_next,
     RmOff result = 0;
     bool done = FALSE;
     bool first = TRUE;
+    struct fiemap_extent fm_last;
 
-    /* used for detecting contiguous extents */
-    unsigned long expected = 0;
+    memset(&fm_last, 0, sizeof(fm_last));
 
     fsync(fd);
 
@@ -1061,7 +1061,9 @@ RmOff rm_offset_get_from_fd(int fd, RmOff file_offset, RmOff *file_offset_next,
                 first = FALSE;
             } else {
                 /* check if subsequent extents are contiguous */
-                if(fm_ext.fe_physical != expected)  {
+                unsigned long expected_dense = fm_last.fe_physical + fm_last.fe_length;
+                unsigned long expected = fm_last.fe_physical + fm_ext.fe_logical - fm_last.fe_logical;
+                if(fm_ext.fe_physical != expected || fm_ext.fe_physical != expected_dense) {
                     /* current extent is not contiguous with previous, so we can stop */
                     g_free(fm);
                     break;
@@ -1083,7 +1085,7 @@ RmOff rm_offset_get_from_fd(int fd, RmOff file_offset, RmOff *file_offset_next,
 
             /* move offsets in preparation for reading next extent */
             file_offset = fm_ext.fe_logical + fm_ext.fe_length;
-            expected = fm_ext.fe_physical + fm_ext.fe_length;
+            fm_last = fm_ext;
         }
 
         g_free(fm);

tests/test_mains/test_is_reflink.py

@@ -142,26 +142,45 @@ def _copy_file_range(src, dst, count, offset_src, offset_dst):
         raise RuntimeError('copy_file_range only copied {} bytes (expected {})'.format(bytes_copied, count))
 
 
-# GitHub issue #611: Make sure holes can be detected when the physical offsets and logical
-# extent ends are otherwise the same.
-@needs_reflink_fs
-@with_setup(usual_setup_func, usual_teardown_func)
-def test_hole_before_extent():
+def kb(n):
+    return 1024 * n
+
+
+def _hole_testcase_inner(extents):
     path_a = os.path.join(TESTDIR_NAME, 'a')
     path_b = os.path.join(TESTDIR_NAME, 'b')
 
-    def kb(n): return 1024 * n
-
-    _run_dd_urandom(path_a, '8K', 2)
+    _run_dd_urandom(path_a, kb(16) // extents, extents)
     with open(path_b, 'wb') as f:
         os.truncate(f.fileno(), kb(16))  # same-sized file with no extents
 
     with open(path_a, 'rb') as fsrc, open(path_b, 'wb') as fdst:
         infd, outfd = fsrc.fileno(), fdst.fileno()
+        yield infd, outfd
+
+    # expect RM_LINK_NONE
+    check_is_reflink_status(1, path_a, path_b)
+
+
+# GitHub issue #611: Make sure holes can be detected when the physical offsets and logical
+# extent ends are otherwise the same.
+@needs_reflink_fs
+@with_setup(usual_setup_func, usual_teardown_func)
+def test_hole_before_extent():
+    for infd, outfd in _hole_testcase_inner(extents=2):
         # copy first half of first extent with 4K offset
         _copy_file_range(infd, outfd, kb(4), kb(0), kb(4))
         # copy second extent
         _copy_file_range(infd, outfd, kb(8), kb(8), kb(8))
 
-    # expect RM_LINK_NONE
-    check_is_reflink_status(1, path_a, path_b)
+
+# GitHub issue #530: Make sure physically adjacent extents aren't merged if there is a
+# hole between them logically.
+@needs_reflink_fs
+@with_setup(usual_setup_func, usual_teardown_func)
+def test_hole_between_extents():
+    for infd, outfd in _hole_testcase_inner(extents=1):
+        # copy first extent
+        _copy_file_range(infd, outfd, kb(8), kb(0), kb(0))
+        # copy first half of second extent with 4K offset
+        _copy_file_range(infd, outfd, kb(4), kb(8), kb(12))