Re: [PATCH v2 10/27] libbtrfsutil: add btrfs_util_[gs]et_default_subvolume()

["Misono, Tomohiro" <misono.tomohiro@jp.fujitsu.com>]

On 2018/02/16 4:04, Omar Sandoval wrote:
> From: Omar Sandoval <osandov@fb.com>
> 
> set_default_subvolume() is a trivial ioctl(), but there's no ioctl() for
> get_default_subvolume(), so we need to search the root tree.
> 
> Signed-off-by: Omar Sandoval <osandov@fb.com>
> ---
>  libbtrfsutil/btrfsutil.h                    |  41 ++++++++++
>  libbtrfsutil/python/btrfsutilpy.h           |   2 +
>  libbtrfsutil/python/module.c                |  14 ++++
>  libbtrfsutil/python/subvolume.c             |  50 ++++++++++++
>  libbtrfsutil/python/tests/test_subvolume.py |  14 ++++
>  libbtrfsutil/subvolume.c                    | 113 ++++++++++++++++++++++++++++
>  6 files changed, 234 insertions(+)
> 
> diff --git a/libbtrfsutil/btrfsutil.h b/libbtrfsutil/btrfsutil.h
> index 8bd2b847..54777f1d 100644
> --- a/libbtrfsutil/btrfsutil.h
> +++ b/libbtrfsutil/btrfsutil.h
> @@ -256,6 +256,8 @@ enum btrfs_util_error btrfs_util_get_subvolume_read_only_fd(int fd, bool *ret);
>   * @path: Subvolume path.
>   * @read_only: New value of read-only flag.
>   *
> + * This requires appropriate privilege (CAP_SYS_ADMIN).
> + *
>   * Return: %BTRFS_UTIL_OK on success, non-zero error code on failure.
>   */
>  enum btrfs_util_error btrfs_util_set_subvolume_read_only(const char *path,
> @@ -268,6 +270,45 @@ enum btrfs_util_error btrfs_util_set_subvolume_read_only(const char *path,
>  enum btrfs_util_error btrfs_util_set_subvolume_read_only_fd(int fd,
>  							    bool read_only);
>  
> +/**
> + * btrfs_util_get_default_subvolume() - Get the default subvolume for a
> + * filesystem.
> + * @path: Path on a Btrfs filesystem.
> + * @id_ret: Returned subvolume ID.
> + *
> + * This requires appropriate privilege (CAP_SYS_ADMIN).
> + *
> + * Return: %BTRFS_UTIL_OK on success, non-zero error code on failure.
> + */
> +enum btrfs_util_error btrfs_util_get_default_subvolume(const char *path,
> +						       uint64_t *id_ret);
> +
> +/**
> + * btrfs_util_get_default_subvolume_fd() - See
> + * btrfs_util_get_default_subvolume().
> + */
> +enum btrfs_util_error btrfs_util_get_default_subvolume_fd(int fd,
> +							  uint64_t *id_ret);
> +
> +/**
> + * btrfs_util_set_default_subvolume() - Set the default subvolume for a
> + * filesystem.
> + * @path: Path in a Btrfs filesystem. This may be any path in the filesystem; it
> + * does not have to refer to a subvolume unless @id is zero.
> + * @id: ID of subvolume to set as the default. If zero is given, the subvolume
> + * ID of @path is used.

The line "This requires appropriate privilege (CAP_SYS_ADMIN)." is missing here.

> + *
> + * Return: %BTRFS_UTIL_OK on success, non-zero error code on failure.
> + */
> +enum btrfs_util_error btrfs_util_set_default_subvolume(const char *path,
> +						       uint64_t id);
> +
> +/**
> + * btrfs_util_set_default_subvolume_fd() - See
> + * btrfs_util_set_default_subvolume().
> + */
> +enum btrfs_util_error btrfs_util_set_default_subvolume_fd(int fd, uint64_t id);
> +
>  struct btrfs_util_qgroup_inherit;
>  
>  /**
> diff --git a/libbtrfsutil/python/btrfsutilpy.h b/libbtrfsutil/python/btrfsutilpy.h
> index 21253e51..41314d4a 100644
> --- a/libbtrfsutil/python/btrfsutilpy.h
> +++ b/libbtrfsutil/python/btrfsutilpy.h
> @@ -66,6 +66,8 @@ PyObject *subvolume_path(PyObject *self, PyObject *args, PyObject *kwds);
>  PyObject *subvolume_info(PyObject *self, PyObject *args, PyObject *kwds);
>  PyObject *get_subvolume_read_only(PyObject *self, PyObject *args, PyObject *kwds);
>  PyObject *set_subvolume_read_only(PyObject *self, PyObject *args, PyObject *kwds);
> +PyObject *get_default_subvolume(PyObject *self, PyObject *args, PyObject *kwds);
> +PyObject *set_default_subvolume(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 3395fb14..0ac4d63a 100644
> --- a/libbtrfsutil/python/module.c
> +++ b/libbtrfsutil/python/module.c
> @@ -173,6 +173,20 @@ static PyMethodDef btrfsutil_methods[] = {
>  	 "Arguments:\n"
>  	 "path -- string, bytes, path-like object, or open file descriptor\n"
>  	 "read_only -- bool flag value"},
> +	{"get_default_subvolume", (PyCFunction)get_default_subvolume,
> +	 METH_VARARGS | METH_KEYWORDS,
> +	 "get_default_subvolume(path) -> int\n\n"
> +	 "Get the ID of the default subvolume of a filesystem.\n\n"
> +	 "Arguments:\n"
> +	 "path -- string, bytes, path-like object, or open file descriptor"},
> +	{"set_default_subvolume", (PyCFunction)set_default_subvolume,
> +	 METH_VARARGS | METH_KEYWORDS,
> +	 "set_default_subvolume(path, id=0)\n\n"
> +	 "Set the default subvolume of a filesystem.\n\n"
> +	 "Arguments:\n"
> +	 "path -- string, bytes, path-like object, or open file descriptor\n"
> +	 "id -- if not zero, set the default subvolume to the subvolume with\n"
> +	 "this ID instead of the given path"},
>  	{"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 76487865..fa3ec4a7 100644
> --- a/libbtrfsutil/python/subvolume.c
> +++ b/libbtrfsutil/python/subvolume.c
> @@ -270,6 +270,56 @@ PyObject *set_subvolume_read_only(PyObject *self, PyObject *args, PyObject *kwds
>  	Py_RETURN_NONE;
>  }
>  
> +PyObject *get_default_subvolume(PyObject *self, PyObject *args, PyObject *kwds)
> +{
> +	static char *keywords[] = {"path", NULL};
> +	struct path_arg path = {.allow_fd = true};
> +	enum btrfs_util_error err;
> +	uint64_t id;
> +
> +	if (!PyArg_ParseTupleAndKeywords(args, kwds, "O&:get_default_subvolume",
> +					 keywords, &path_converter, &path))
> +		return NULL;
> +
> +	if (path.path)
> +		err = btrfs_util_get_default_subvolume(path.path, &id);
> +	else
> +		err = btrfs_util_get_default_subvolume_fd(path.fd, &id);
> +	if (err) {
> +		SetFromBtrfsUtilErrorWithPath(err, &path);
> +		path_cleanup(&path);
> +		return NULL;
> +	}
> +
> +	path_cleanup(&path);
> +	return PyLong_FromUnsignedLongLong(id);
> +}
> +
> +PyObject *set_default_subvolume(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;
> +
> +	if (!PyArg_ParseTupleAndKeywords(args, kwds, "O&|K:set_default_subvolume",
> +					 keywords, &path_converter, &path, &id))
> +		return NULL;
> +
> +	if (path.path)
> +		err = btrfs_util_set_default_subvolume(path.path, id);
> +	else
> +		err = btrfs_util_set_default_subvolume_fd(path.fd, id);
> +	if (err) {
> +		SetFromBtrfsUtilErrorWithPath(err, &path);
> +		path_cleanup(&path);
> +		return NULL;
> +	}
> +
> +	path_cleanup(&path);
> +	Py_RETURN_NONE;
> +}
> +
>  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 23871de9..937a4397 100644
> --- a/libbtrfsutil/python/tests/test_subvolume.py
> +++ b/libbtrfsutil/python/tests/test_subvolume.py
> @@ -154,6 +154,20 @@ class TestSubvolume(BtrfsTestCase):
>  
>                  btrfsutil.set_subvolume_read_only(arg, False)
>  
> +    def test_default_subvolume(self):
> +        for arg in self.path_or_fd(self.mountpoint):
> +            with self.subTest(type=type(arg)):
> +                self.assertEqual(btrfsutil.get_default_subvolume(arg), 5)
> +
> +        subvol = os.path.join(self.mountpoint, 'subvol')
> +        btrfsutil.create_subvolume(subvol)
> +        for arg in self.path_or_fd(subvol):
> +            with self.subTest(type=type(arg)):
> +                btrfsutil.set_default_subvolume(arg)
> +                self.assertEqual(btrfsutil.get_default_subvolume(arg), 256)
> +                btrfsutil.set_default_subvolume(arg, 5)
> +                self.assertEqual(btrfsutil.get_default_subvolume(arg), 5)
> +
>      def test_create_subvolume(self):
>          subvol = os.path.join(self.mountpoint, 'subvol')
>  
> diff --git a/libbtrfsutil/subvolume.c b/libbtrfsutil/subvolume.c
> index bc5b309e..b3f768ed 100644
> --- a/libbtrfsutil/subvolume.c
> +++ b/libbtrfsutil/subvolume.c
> @@ -467,6 +467,119 @@ PUBLIC enum btrfs_util_error btrfs_util_set_subvolume_read_only_fd(int fd,
>  	return BTRFS_UTIL_OK;
>  }
>  
> +PUBLIC enum btrfs_util_error btrfs_util_get_default_subvolume(const char *path,
> +							      uint64_t *id_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_default_subvolume_fd(fd, id_ret);
> +	SAVE_ERRNO_AND_CLOSE(fd);
> +	return err;
> +}
> +
> +PUBLIC enum btrfs_util_error btrfs_util_get_default_subvolume_fd(int fd,
> +								 uint64_t *id_ret)
> +{
> +	struct btrfs_ioctl_search_args search = {
> +		.key = {
> +			.tree_id = BTRFS_ROOT_TREE_OBJECTID,
> +			.min_objectid = BTRFS_ROOT_TREE_DIR_OBJECTID,
> +			.max_objectid = BTRFS_ROOT_TREE_DIR_OBJECTID,
> +			.min_type = BTRFS_DIR_ITEM_KEY,
> +			.max_type = BTRFS_DIR_ITEM_KEY,
> +			.min_offset = 0,
> +			.max_offset = UINT64_MAX,
> +			.min_transid = 0,
> +			.max_transid = UINT64_MAX,
> +			.nr_items = 0,
> +		},
> +	};
> +	size_t items_pos = 0, buf_off = 0;
> +	int ret;
> +
> +	for (;;) {
> +		const struct btrfs_ioctl_search_header *header;
> +
> +		if (items_pos >= search.key.nr_items) {
> +			search.key.nr_items = 4096;
> +			ret = ioctl(fd, BTRFS_IOC_TREE_SEARCH, &search);
> +			if (ret == -1)
> +				return BTRFS_UTIL_ERROR_SEARCH_FAILED;
> +			items_pos = 0;
> +			buf_off = 0;
> +
> +			if (search.key.nr_items == 0) {
> +				errno = ENOENT;
> +				return BTRFS_UTIL_ERROR_SUBVOLUME_NOT_FOUND;
> +			}
> +		}
> +
> +		header = (struct btrfs_ioctl_search_header *)(search.buf + buf_off);
> +		if (header->type == BTRFS_DIR_ITEM_KEY) {
> +			const struct btrfs_dir_item *dir;
> +			const char *name;
> +			uint16_t name_len;
> +
> +			dir = (struct btrfs_dir_item *)(header + 1);
> +			name = (const char *)(dir + 1);
> +			name_len = le16_to_cpu(dir->name_len);
> +			if (strncmp(name, "default", name_len) == 0) {
> +				*id_ret = le64_to_cpu(dir->location.objectid);
> +				break;
> +			}
> +		}
> +
> +		items_pos++;
> +		buf_off += sizeof(*header) + header->len;
> +		search.key.min_offset = header->offset + 1;
> +	}
> +
> +	return BTRFS_UTIL_OK;
> +}
> +
> +PUBLIC enum btrfs_util_error btrfs_util_set_default_subvolume(const char *path,
> +							      uint64_t id)
> +{
> +	enum btrfs_util_error err;
> +	int fd;
> +
> +	fd = open(path, O_RDONLY);
> +	if (fd == -1)
> +		return BTRFS_UTIL_ERROR_OPEN_FAILED;
> +
> +	err = btrfs_util_set_default_subvolume_fd(fd, id);
> +	SAVE_ERRNO_AND_CLOSE(fd);
> +	return err;
> +}
> +
> +PUBLIC enum btrfs_util_error btrfs_util_set_default_subvolume_fd(int fd,
> +								 uint64_t id)
> +{
> +	enum btrfs_util_error err;
> +	int ret;
> +
> +	if (id == 0) {
> +		err = btrfs_util_is_subvolume_fd(fd);
> +		if (err)
> +			return err;
> +
> +		err = btrfs_util_subvolume_id_fd(fd, &id);
> +		if (err)
> +			return err;
> +	}
> +
> +	ret = ioctl(fd, BTRFS_IOC_DEFAULT_SUBVOL, &id);
> +	if (ret == -1)
> +		return BTRFS_UTIL_ERROR_DEFAULT_SUBVOL_FAILED;
> +
> +	return BTRFS_UTIL_OK;
> +}
> +
>  static enum btrfs_util_error openat_parent_and_name(int dirfd, const char *path,
>  						    char *name, size_t name_len,
>  						    int *fd)
>