libbtrfsutil: add btrfs_util_get_label

libbtrfsutil/README.md

@@ -479,6 +479,7 @@ everywhere. The following checklist should help to make sure nothing is missing:
 ### API summary
 
 * filesystem
+  * get_label
   * sync
   * wait for sync
 * subvolume

libbtrfsutil/btrfsutil.h

@@ -67,6 +67,7 @@ enum btrfs_util_error {
 	BTRFS_UTIL_ERROR_GET_SUBVOL_ROOTREF_FAILED,
 	BTRFS_UTIL_ERROR_INO_LOOKUP_USER_FAILED,
 	BTRFS_UTIL_ERROR_FS_INFO_FAILED,
+	BTRFS_UTIL_ERROR_FS_GET_LABEL_FAILED,
 };
 
 /**
@@ -78,6 +79,24 @@ enum btrfs_util_error {
  */
 const char *btrfs_util_strerror(enum btrfs_util_error err);
 
+/**
+ * btrfs_util_get_label() - Get the filesystem label for a
+ * filesystem.
+ * @path: Path on a Btrfs filesystem.
+ * @label: Returned filesytem label.
+ *
+ * Return: %BTRFS_UTIL_OK on success, non-zero error code on failure.
+ */
+enum btrfs_util_error btrfs_util_get_label(const char *path,
+					   char **label);
+
+/**
+ * btrfs_util_get_label_fd() - See
+ * btrfs_util_get_label().
+ */
+enum btrfs_util_error btrfs_util_get_label_fd(int fd,
+					      char **label);
+
 /**
  * btrfs_util_sync() - Force a sync on a specific Btrfs filesystem.
  * @path: Path on a Btrfs filesystem.

libbtrfsutil/errors.c

@@ -53,6 +53,8 @@ static const char * const error_messages[] = {
 		"Could not resolve subvolume path with BTRFS_IOC_INO_LOOKUP_USER",
 	[BTRFS_UTIL_ERROR_FS_INFO_FAILED] =
 		"Could not get filesystem information",
+	[BTRFS_UTIL_ERROR_FS_GET_LABEL_FAILED] =
+		"Could not get filesystem label",
 };
 
 PUBLIC const char *btrfs_util_strerror(enum btrfs_util_error err)

libbtrfsutil/filesystem.c

@@ -19,11 +19,52 @@
 
 #include <stddef.h>
 #include <stdint.h>
+#include <stdlib.h>
 #include <fcntl.h>
 #include <sys/ioctl.h>
 
 #include "btrfsutil_internal.h"
 
+
+PUBLIC enum btrfs_util_error btrfs_util_get_label(const char *path,
+						  char **label_ret)
+{
+	enum btrfs_util_error err;
+	int fd;
+
+	fd = open(path, O_RDONLY);
+	if (fd == -1)
+		return BTRFS_UTIL_ERROR_OPEN_FAILED;
+
+	err = btrfs_util_get_label_fd(fd, label_ret);
+	if (err)
+		return err;
+
+	return BTRFS_UTIL_OK;
+}
+
+PUBLIC enum btrfs_util_error btrfs_util_get_label_fd(int fd,
+						     char **label_ret)
+{
+	int ret;
+	size_t len;
+
+	char label[BTRFS_PATH_NAME_MAX];
+	ret = ioctl(fd, BTRFS_IOC_GET_FSLABEL, label);
+	if (ret == -1)
+		return BTRFS_UTIL_ERROR_SUBVOL_SETFLAGS_FAILED;
+
+	len = strlen(label);
+	*label_ret = malloc(len + 1);
+	if (!*label_ret)
+		return BTRFS_UTIL_ERROR_NO_MEMORY;
+
+	memcpy(*label_ret, label, len);
+	label_ret[len] = '\0';
+
+	return BTRFS_UTIL_OK;
+}
+
 PUBLIC enum btrfs_util_error btrfs_util_sync(const char *path)
 {
 	enum btrfs_util_error err;

libbtrfsutil/libbtrfsutil.sym

@@ -16,6 +16,8 @@ global:
 	btrfs_util_destroy_subvolume_iterator;
 	btrfs_util_get_default_subvolume;
 	btrfs_util_get_default_subvolume_fd;
+	btrfs_util_get_label;
+	btrfs_util_get_label_fd;
 	btrfs_util_get_subvolume_read_only;
 	btrfs_util_get_subvolume_read_only_fd;
 	btrfs_util_is_subvolume;

libbtrfsutil/python/btrfsutilpy.h

@@ -63,6 +63,7 @@ void SetFromBtrfsUtilErrorWithPaths(enum btrfs_util_error err,
 				    struct path_arg *path1,
 				    struct path_arg *path2);
 
+PyObject *filesystem_get_label(PyObject *self, PyObject *args, PyObject *kwds);
 PyObject *filesystem_sync(PyObject *self, PyObject *args, PyObject *kwds);
 PyObject *start_sync(PyObject *self, PyObject *args, PyObject *kwds);
 PyObject *wait_sync(PyObject *self, PyObject *args, PyObject *kwds);

libbtrfsutil/python/filesystem.c

@@ -19,6 +19,31 @@
 
 #include "btrfsutilpy.h"
 
+PyObject *filesystem_get_label(PyObject *self, PyObject *args, PyObject *kwds)
+{
+	static char *keywords[] = {"path", NULL};
+	struct path_arg path = {.allow_fd = true};
+	enum btrfs_util_error err;
+	char *label;
+
+	if (!PyArg_ParseTupleAndKeywords(args, kwds, "O&:get_label", keywords,
+					 &path_converter, &path))
+		return NULL;
+
+	if (path.path)
+		err = btrfs_util_get_label(path.path, &label);
+	else
+		err = btrfs_util_get_label_fd(path.fd, &label);
+	if (err) {
+		SetFromBtrfsUtilErrorWithPath(err, &path);
+		path_cleanup(&path);
+		return NULL;
+	}
+
+	path_cleanup(&path);
+	return PyUnicode_FromString(label);
+}
+
 PyObject *filesystem_sync(PyObject *self, PyObject *args, PyObject *kwds)
 {
 	static char *keywords[] = {"path", NULL};

libbtrfsutil/python/module.c

@@ -155,6 +155,12 @@ void path_cleanup(struct path_arg *path)
 }
 
 static PyMethodDef btrfsutil_methods[] = {
+	{"get_label", (PyCFunction)filesystem_get_label,
+	 METH_VARARGS | METH_KEYWORDS,
+	 "get_label(path)\n\n"
+	 "Get the filesystem label.\n\n"
+	 "Arguments:\n"
+	 "path -- string, bytes, path-like object, or open file descriptor"},
 	{"sync", (PyCFunction)filesystem_sync,
 	 METH_VARARGS | METH_KEYWORDS,
 	 "sync(path)\n\n"

libbtrfsutil/python/tests/test_filesystem.py

@@ -71,3 +71,7 @@ def test_wait_sync(self):
                 new_generation = self.super_generation()
                 self.assertGreater(new_generation, old_generation)
                 old_generation = new_generation
+
+    def test_get_label(self):
+        label = btrfsutil.get_label(self.mountpoint)
+        self.assertIsNotNone(label)