libbtrfsutil: add btrfs_util_subvolume_path()

We can just walk up root backrefs with BTRFS_IOC_TREE_SEARCH and inode
paths with BTRFS_IOC_INO_LOOKUP.

Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: David Sterba <dsterba@suse.com>

4 files changed, 70 insertions, 0 deletions

diff --git a/libbtrfsutil/python/btrfsutilpy.h b/libbtrfsutil/python/btrfsutilpy.h
index 19ba71f3..1fd475b4 100644
--- a/libbtrfsutil/python/btrfsutilpy.h
+++ b/libbtrfsutil/python/btrfsutilpy.h
@@ -63,6 +63,7 @@ PyObject *start_sync(PyObject *self, PyObject *args, PyObject *kwds);
 PyObject *wait_sync(PyObject *self, PyObject *args, PyObject *kwds);
 PyObject *is_subvolume(PyObject *self, PyObject *args, PyObject *kwds);
 PyObject *subvolume_id(PyObject *self, PyObject *args, PyObject *kwds);
+PyObject *subvolume_path(PyObject *self, PyObject *args, PyObject *kwds);
 PyObject *create_subvolume(PyObject *self, PyObject *args, PyObject *kwds);
 
 void add_module_constants(PyObject *m);
diff --git a/libbtrfsutil/python/module.c b/libbtrfsutil/python/module.c
index deb26875..455e909a 100644
--- a/libbtrfsutil/python/module.c
+++ b/libbtrfsutil/python/module.c
@@ -165,6 +165,14 @@ static PyMethodDef btrfsutil_methods[] = {
 	 "Get the ID of the subvolume containing a file.\n\n"
 	 "Arguments:\n"
 	 "path -- string, bytes, path-like object, or open file descriptor"},
+	{"subvolume_path", (PyCFunction)subvolume_path,
+	 METH_VARARGS | METH_KEYWORDS,
+	 "subvolume_path(path, id=0) -> int\n\n"
+	 "Get the path of a subvolume relative to the filesystem root.\n\n"
+	 "Arguments:\n"
+	 "path -- string, bytes, path-like object, or open file descriptor\n"
+	 "id -- if not zero, instead of returning the subvolume path of the\n"
+	 "given path, return the path of the subvolume with this ID"},
 	{"create_subvolume", (PyCFunction)create_subvolume,
 	 METH_VARARGS | METH_KEYWORDS,
 	 "create_subvolume(path, async=False)\n\n"
diff --git a/libbtrfsutil/python/subvolume.c b/libbtrfsutil/python/subvolume.c
index 6f2080ee..6382d290 100644
--- a/libbtrfsutil/python/subvolume.c
+++ b/libbtrfsutil/python/subvolume.c
@@ -72,6 +72,36 @@ PyObject *subvolume_id(PyObject *self, PyObject *args, PyObject *kwds)
 	return PyLong_FromUnsignedLongLong(id);
 }
 
+PyObject *subvolume_path(PyObject *self, PyObject *args, PyObject *kwds)
+{
+	static char *keywords[] = {"path", "id", NULL};
+	struct path_arg path = {.allow_fd = true};
+	enum btrfs_util_error err;
+	uint64_t id = 0;
+	char *subvol_path;
+	PyObject *ret;
+
+	if (!PyArg_ParseTupleAndKeywords(args, kwds, "O&|K:subvolume_path",
+					 keywords, &path_converter, &path, &id))
+		return NULL;
+
+	if (path.path)
+		err = btrfs_util_subvolume_path(path.path, id, &subvol_path);
+	else
+		err = btrfs_util_subvolume_path_fd(path.fd, id, &subvol_path);
+	if (err) {
+		SetFromBtrfsUtilErrorWithPath(err, &path);
+		path_cleanup(&path);
+		return NULL;
+	}
+
+	path_cleanup(&path);
+
+	ret = PyUnicode_DecodeFSDefault(subvol_path);
+	free(subvol_path);
+	return ret;
+}
+
 PyObject *create_subvolume(PyObject *self, PyObject *args, PyObject *kwds)
 {
 	static char *keywords[] = {"path", "async", "qgroup_inherit", NULL};
diff --git a/libbtrfsutil/python/tests/test_subvolume.py b/libbtrfsutil/python/tests/test_subvolume.py
index f6c5958d..57ba27bf 100644
--- a/libbtrfsutil/python/tests/test_subvolume.py
+++ b/libbtrfsutil/python/tests/test_subvolume.py
@@ -56,6 +56,37 @@ class TestSubvolume(BtrfsTestCase):
             with self.subTest(type=type(arg)):
                 self.assertEqual(btrfsutil.subvolume_id(arg), 5)
 
+    def test_subvolume_path(self):
+        btrfsutil.create_subvolume(os.path.join(self.mountpoint, 'subvol1'))
+        os.mkdir(os.path.join(self.mountpoint, 'dir1'))
+        os.mkdir(os.path.join(self.mountpoint, 'dir1/dir2'))
+        btrfsutil.create_subvolume(os.path.join(self.mountpoint, 'dir1/dir2/subvol2'))
+        btrfsutil.create_subvolume(os.path.join(self.mountpoint, 'dir1/dir2/subvol2/subvol3'))
+        os.mkdir(os.path.join(self.mountpoint, 'subvol1/dir3'))
+        btrfsutil.create_subvolume(os.path.join(self.mountpoint, 'subvol1/dir3/subvol4'))
+
+        for arg in self.path_or_fd(self.mountpoint):
+            with self.subTest(type=type(arg)):
+                self.assertEqual(btrfsutil.subvolume_path(arg), '')
+                self.assertEqual(btrfsutil.subvolume_path(arg, 5), '')
+                self.assertEqual(btrfsutil.subvolume_path(arg, 256), 'subvol1')
+                self.assertEqual(btrfsutil.subvolume_path(arg, 257), 'dir1/dir2/subvol2')
+                self.assertEqual(btrfsutil.subvolume_path(arg, 258), 'dir1/dir2/subvol2/subvol3')
+                self.assertEqual(btrfsutil.subvolume_path(arg, 259), 'subvol1/dir3/subvol4')
+
+        pwd = os.getcwd()
+        try:
+            os.chdir(self.mountpoint)
+            path = ''
+            for i in range(26):
+                name = chr(ord('a') + i) * 255
+                path = os.path.join(path, name)
+                btrfsutil.create_subvolume(name)
+                os.chdir(name)
+            self.assertEqual(btrfsutil.subvolume_path('.'), path)
+        finally:
+            os.chdir(pwd)
+
     def test_create_subvolume(self):
         subvol = os.path.join(self.mountpoint, 'subvol')