[PATCH v2 12/27] libbtrfsutil: add btrfs_util_create_snapshot()

[Omar Sandoval <osandov@osandov.com>]

From: Omar Sandoval <osandov@fb.com>

Thanks to subvolume iterators, we can also implement recursive snapshot
fairly easily.

Signed-off-by: Omar Sandoval <osandov@fb.com>
---
 libbtrfsutil/btrfsutil.h                    |  59 ++++++++++
 libbtrfsutil/python/btrfsutilpy.h           |   1 +
 libbtrfsutil/python/module.c                |  11 ++
 libbtrfsutil/python/subvolume.c             |  49 ++++++++
 libbtrfsutil/python/tests/test_qgroup.py    |  10 ++
 libbtrfsutil/python/tests/test_subvolume.py |  55 +++++++++
 libbtrfsutil/subvolume.c                    | 167 ++++++++++++++++++++++++++++
 7 files changed, 352 insertions(+)

diff --git a/libbtrfsutil/btrfsutil.h b/libbtrfsutil/btrfsutil.h
index 7d3a87f6..04fe6666 100644
--- a/libbtrfsutil/btrfsutil.h
+++ b/libbtrfsutil/btrfsutil.h
@@ -345,6 +345,65 @@ enum btrfs_util_error btrfs_util_create_subvolume_fd(int parent_fd,
 						     uint64_t *async_transid,
 						     struct btrfs_util_qgroup_inherit *qgroup_inherit);
 
+/**
+ * BTRFS_UTIL_CREATE_SNAPSHOT_RECURSIVE - Also snapshot subvolumes beneath the
+ * source subvolume onto the same location on the new snapshot.
+ *
+ * Note that this is currently implemented in userspace non-atomically. Because
+ * it modifies the newly-created snapshot, it cannot be combined with
+ * %BTRFS_UTIL_CREATE_SNAPSHOT_READ_ONLY. It requires appropriate privilege
+ * (CAP_SYS_ADMIN).
+ */
+#define BTRFS_UTIL_CREATE_SNAPSHOT_RECURSIVE (1 << 0)
+/**
+ * BTRFS_UTIL_CREATE_SNAPSHOT_READ_ONLY - Create a read-only snapshot.
+ */
+#define BTRFS_UTIL_CREATE_SNAPSHOT_READ_ONLY (1 << 1)
+#define BTRFS_UTIL_CREATE_SNAPSHOT_MASK ((1 << 2) - 1)
+
+/**
+ * btrfs_util_create_snapshot() - Create a new snapshot from a source subvolume
+ * path.
+ * @source: Path of the existing subvolume to snapshot.
+ * @path: Where to create the snapshot.
+ * @flags: Bitmask of BTRFS_UTIL_CREATE_SNAPSHOT_* flags.
+ * @async_transid: See btrfs_util_create_subvolume(). If
+ * %BTRFS_UTIL_CREATE_SNAPSHOT_RECURSIVE was in @flags, then this will contain
+ * the largest transaction ID of all created subvolumes.
+ * @qgroup_inherit: See btrfs_util_create_subvolume().
+ *
+ * Return: %BTRFS_UTIL_OK on success, non-zero error code on failure.
+ */
+enum btrfs_util_error btrfs_util_create_snapshot(const char *source,
+						 const char *path, int flags,
+						 uint64_t *async_transid,
+						 struct btrfs_util_qgroup_inherit *qgroup_inherit);
+
+/**
+ * btrfs_util_create_snapshot_fd() - See btrfs_util_create_snapshot().
+ */
+enum btrfs_util_error btrfs_util_create_snapshot_fd(int fd, const char *path,
+						    int flags,
+						    uint64_t *async_transid,
+						    struct btrfs_util_qgroup_inherit *qgroup_inherit);
+
+/**
+ * btrfs_util_create_snapshot_fd2() - Create a new snapshot from a source
+ * subvolume file descriptor and a target parent file descriptor and name.
+ * @fd: File descriptor of the existing subvolume to snapshot.
+ * @parent_fd: File descriptor of the parent directory where the snapshot should
+ * be created.
+ * @name: Name of the snapshot to create.
+ * @flags: See btrfs_util_create_snapshot().
+ * @async_transid: See btrfs_util_create_snapshot().
+ * @qgroup_inherit: See btrfs_util_create_snapshot().
+ */
+enum btrfs_util_error btrfs_util_create_snapshot_fd2(int fd, int parent_fd,
+						     const char *name,
+						     int flags,
+						     uint64_t *async_transid,
+						     struct btrfs_util_qgroup_inherit *qgroup_inherit);
+
 struct btrfs_util_subvolume_iterator;
 
 /**
diff --git a/libbtrfsutil/python/btrfsutilpy.h b/libbtrfsutil/python/btrfsutilpy.h
index a9c15219..d552e416 100644
--- a/libbtrfsutil/python/btrfsutilpy.h
+++ b/libbtrfsutil/python/btrfsutilpy.h
@@ -70,6 +70,7 @@ 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);
+PyObject *create_snapshot(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 daf0747f..d8f797cb 100644
--- a/libbtrfsutil/python/module.c
+++ b/libbtrfsutil/python/module.c
@@ -195,6 +195,17 @@ static PyMethodDef btrfsutil_methods[] = {
 	 "path -- string, bytes, or path-like object\n"
 	 "async -- create the subvolume without waiting for it to commit to\n"
 	 "disk and return the transaction ID"},
+	{"create_snapshot", (PyCFunction)create_snapshot,
+	 METH_VARARGS | METH_KEYWORDS,
+	 "create_snapshot(source, path, recursive=False, read_only=False, async=False)\n\n"
+	 "Create a new snapshot.\n\n"
+	 "Arguments:\n"
+	 "source -- string, bytes, path-like object, or open file descriptor\n"
+	 "path -- string, bytes, or path-like object\n"
+	 "recursive -- also snapshot child subvolumes\n"
+	 "read_only -- create a read-only snapshot\n"
+	 "async -- create the subvolume without waiting for it to commit to\n"
+	 "disk and return the transaction ID"},
 	{},
 };
 
diff --git a/libbtrfsutil/python/subvolume.c b/libbtrfsutil/python/subvolume.c
index 6c384583..a158ade7 100644
--- a/libbtrfsutil/python/subvolume.c
+++ b/libbtrfsutil/python/subvolume.c
@@ -349,6 +349,55 @@ PyObject *create_subvolume(PyObject *self, PyObject *args, PyObject *kwds)
 		Py_RETURN_NONE;
 }
 
+PyObject *create_snapshot(PyObject *self, PyObject *args, PyObject *kwds)
+{
+	static char *keywords[] = {
+		"source", "path", "recursive", "read_only", "async",
+		"qgroup_inherit", NULL,
+	};
+	struct path_arg src = {.allow_fd = true}, dst = {.allow_fd = false};
+	enum btrfs_util_error err;
+	int recursive = 0, read_only = 0, async = 0;
+	int flags = 0;
+	QgroupInherit *inherit = NULL;
+	uint64_t transid;
+
+	if (!PyArg_ParseTupleAndKeywords(args, kwds, "O&O&|pppO!:create_snapshot",
+					 keywords, &path_converter, &src,
+					 &path_converter, &dst, &recursive,
+					 &read_only, &async,
+					 &QgroupInherit_type, &inherit))
+		return NULL;
+
+	if (recursive)
+		flags |= BTRFS_UTIL_CREATE_SNAPSHOT_RECURSIVE;
+	if (read_only)
+		flags |= BTRFS_UTIL_CREATE_SNAPSHOT_READ_ONLY;
+
+	if (src.path) {
+		err = btrfs_util_create_snapshot(src.path, dst.path, flags,
+						 async ? &transid : NULL,
+						 inherit ? inherit->inherit : NULL);
+	} else {
+		err = btrfs_util_create_snapshot_fd(src.fd, dst.path, flags,
+						    async ? &transid : NULL,
+						    inherit ? inherit->inherit : NULL);
+	}
+	if (err) {
+		SetFromBtrfsUtilErrorWithPaths(err, &src, &dst);
+		path_cleanup(&src);
+		path_cleanup(&dst);
+		return NULL;
+	}
+
+	path_cleanup(&src);
+	path_cleanup(&dst);
+	if (async)
+		return PyLong_FromUnsignedLongLong(transid);
+	else
+		Py_RETURN_NONE;
+}
+
 typedef struct {
 	PyObject_HEAD
 	struct btrfs_util_subvolume_iterator *iter;
diff --git a/libbtrfsutil/python/tests/test_qgroup.py b/libbtrfsutil/python/tests/test_qgroup.py
index 19e6b05a..74fc46b6 100644
--- a/libbtrfsutil/python/tests/test_qgroup.py
+++ b/libbtrfsutil/python/tests/test_qgroup.py
@@ -31,6 +31,16 @@ class TestQgroup(BtrfsTestCase):
 
         btrfsutil.create_subvolume(subvol, qgroup_inherit=inherit)
 
+    def test_snapshot_inherit(self):
+        subvol = os.path.join(self.mountpoint, 'subvol')
+        snapshot = os.path.join(self.mountpoint, 'snapshot')
+
+        inherit = btrfsutil.QgroupInherit()
+        inherit.add_group(5)
+
+        btrfsutil.create_subvolume(subvol)
+        btrfsutil.create_snapshot(subvol, snapshot, qgroup_inherit=inherit)
+
 
 class TestQgroupInherit(unittest.TestCase):
     def test_new(self):
diff --git a/libbtrfsutil/python/tests/test_subvolume.py b/libbtrfsutil/python/tests/test_subvolume.py
index b43beca7..2951154e 100644
--- a/libbtrfsutil/python/tests/test_subvolume.py
+++ b/libbtrfsutil/python/tests/test_subvolume.py
@@ -129,6 +129,13 @@ class TestSubvolume(BtrfsTestCase):
         self.assertEqual(info.stime, 0)
         self.assertEqual(info.rtime, 0)
 
+        subvol_uuid = info.uuid
+        snapshot = os.path.join(self.mountpoint, 'snapshot')
+        btrfsutil.create_snapshot(subvol, snapshot)
+
+        info = btrfsutil.subvolume_info(snapshot)
+        self.assertEqual(info.parent_uuid, subvol_uuid)
+
         # TODO: test received_uuid, stransid, rtransid, stime, and rtime
 
         for arg in self.path_or_fd(self.mountpoint):
@@ -215,6 +222,54 @@ class TestSubvolume(BtrfsTestCase):
         self.assertTrue(os.WIFEXITED(wstatus))
         self.assertEqual(os.WEXITSTATUS(wstatus), 0)
 
+    def test_create_snapshot(self):
+        subvol = os.path.join(self.mountpoint, 'subvol')
+
+        btrfsutil.create_subvolume(subvol)
+        os.mkdir(os.path.join(subvol, 'dir'))
+
+        for i, arg in enumerate(self.path_or_fd(subvol)):
+            with self.subTest(type=type(arg)):
+                snapshots_dir = os.path.join(self.mountpoint, 'snapshots{}'.format(i))
+                os.mkdir(snapshots_dir)
+                snapshot = os.path.join(snapshots_dir, 'snapshot')
+
+                btrfsutil.create_snapshot(subvol, snapshot + '1')
+                self.assertTrue(btrfsutil.is_subvolume(snapshot + '1'))
+                self.assertTrue(os.path.exists(os.path.join(snapshot + '1', 'dir')))
+
+                btrfsutil.create_snapshot(subvol, (snapshot + '2').encode())
+                self.assertTrue(btrfsutil.is_subvolume(snapshot + '2'))
+                self.assertTrue(os.path.exists(os.path.join(snapshot + '2', 'dir')))
+
+                if HAVE_PATH_LIKE:
+                    btrfsutil.create_snapshot(subvol, PurePath(snapshot + '3'))
+                    self.assertTrue(btrfsutil.is_subvolume(snapshot + '3'))
+                    self.assertTrue(os.path.exists(os.path.join(snapshot + '3', 'dir')))
+
+        nested_subvol = os.path.join(subvol, 'nested')
+        more_nested_subvol = os.path.join(nested_subvol, 'more_nested')
+        btrfsutil.create_subvolume(nested_subvol)
+        btrfsutil.create_subvolume(more_nested_subvol)
+        os.mkdir(os.path.join(more_nested_subvol, 'nested_dir'))
+
+        snapshot = os.path.join(self.mountpoint, 'snapshot')
+
+        btrfsutil.create_snapshot(subvol, snapshot + '1')
+        # Dummy subvolume.
+        self.assertEqual(os.stat(os.path.join(snapshot + '1', 'nested')).st_ino, 2)
+        self.assertFalse(os.path.exists(os.path.join(snapshot + '1', 'nested', 'more_nested')))
+
+        btrfsutil.create_snapshot(subvol, snapshot + '2', recursive=True)
+        self.assertTrue(os.path.exists(os.path.join(snapshot + '2', 'nested/more_nested/nested_dir')))
+
+        transid = btrfsutil.create_snapshot(subvol, snapshot + '3', recursive=True, async=True)
+        self.assertTrue(os.path.exists(os.path.join(snapshot + '3', 'nested/more_nested/nested_dir')))
+        self.assertGreater(transid, 0)
+
+        btrfsutil.create_snapshot(subvol, snapshot + '4', read_only=True)
+        self.assertTrue(btrfsutil.get_subvolume_read_only(snapshot + '4'))
+
     def test_subvolume_iterator(self):
         pwd = os.getcwd()
         try:
diff --git a/libbtrfsutil/subvolume.c b/libbtrfsutil/subvolume.c
index 5744f89f..ca3d43c8 100644
--- a/libbtrfsutil/subvolume.c
+++ b/libbtrfsutil/subvolume.c
@@ -836,6 +836,173 @@ out_iter:
 	return err;
 }
 
+static enum btrfs_util_error snapshot_subvolume_children(int fd, int parent_fd,
+							 const char *name,
+							 uint64_t *async_transid)
+{
+	struct btrfs_util_subvolume_iterator *iter;
+	enum btrfs_util_error err;
+	int dstfd;
+
+	dstfd = openat(parent_fd, name, O_RDONLY);
+	if (dstfd == -1)
+		return BTRFS_UTIL_ERROR_OPEN_FAILED;
+
+	err = btrfs_util_create_subvolume_iterator_fd(fd, 0, 0, &iter);
+	if (err)
+		goto out;
+
+	for (;;) {
+		char child_name[BTRFS_SUBVOL_NAME_MAX + 1];
+		char *child_path;
+		int child_fd, new_parent_fd;
+		uint64_t tmp_transid;
+
+		err = btrfs_util_subvolume_iterator_next(iter, &child_path,
+							 NULL);
+		if (err) {
+			if (err == BTRFS_UTIL_ERROR_STOP_ITERATION)
+				err = BTRFS_UTIL_OK;
+			break;
+		}
+
+		/* Remove the placeholder directory. */
+		if (unlinkat(dstfd, child_path, AT_REMOVEDIR) == -1) {
+			free(child_path);
+			err = BTRFS_UTIL_ERROR_RMDIR_FAILED;
+			break;
+		}
+
+		child_fd = openat(fd, child_path, O_RDONLY);
+		if (child_fd == -1) {
+			free(child_path);
+			err = BTRFS_UTIL_ERROR_OPEN_FAILED;
+			break;
+		}
+
+		err = openat_parent_and_name(dstfd, child_path, child_name,
+					     sizeof(child_name),
+					     &new_parent_fd);
+		free(child_path);
+		if (err) {
+			SAVE_ERRNO_AND_CLOSE(child_fd);
+			break;
+		}
+
+		err = btrfs_util_create_snapshot_fd2(child_fd, new_parent_fd,
+						     child_name, 0,
+						     async_transid ? &tmp_transid : NULL,
+						     NULL);
+		SAVE_ERRNO_AND_CLOSE(child_fd);
+		SAVE_ERRNO_AND_CLOSE(new_parent_fd);
+		if (err)
+			break;
+		if (async_transid && tmp_transid > *async_transid)
+			*async_transid = tmp_transid;
+	}
+
+	btrfs_util_destroy_subvolume_iterator(iter);
+out:
+	SAVE_ERRNO_AND_CLOSE(dstfd);
+	return err;
+}
+
+PUBLIC enum btrfs_util_error btrfs_util_create_snapshot(const char *source,
+							const char *path,
+							int flags,
+							uint64_t *async_transid,
+							struct btrfs_util_qgroup_inherit *qgroup_inherit)
+{
+	enum btrfs_util_error err;
+	int fd;
+
+	fd = open(source, O_RDONLY);
+	if (fd == -1)
+		return BTRFS_UTIL_ERROR_OPEN_FAILED;
+
+	err = btrfs_util_create_snapshot_fd(fd, path, flags, async_transid,
+					    qgroup_inherit);
+	SAVE_ERRNO_AND_CLOSE(fd);
+	return err;
+}
+
+PUBLIC enum btrfs_util_error btrfs_util_create_snapshot_fd(int fd,
+							   const char *path,
+							   int flags,
+							   uint64_t *async_transid,
+							   struct btrfs_util_qgroup_inherit *qgroup_inherit)
+{
+	char name[BTRFS_SUBVOL_NAME_MAX + 1];
+	enum btrfs_util_error err;
+	int parent_fd;
+
+	err = openat_parent_and_name(AT_FDCWD, path, name, sizeof(name),
+				     &parent_fd);
+	if (err)
+		return err;
+
+	err = btrfs_util_create_snapshot_fd2(fd, parent_fd, name, flags,
+					     async_transid, qgroup_inherit);
+	SAVE_ERRNO_AND_CLOSE(parent_fd);
+	return err;
+}
+
+PUBLIC enum btrfs_util_error btrfs_util_create_snapshot_fd2(int fd,
+							    int parent_fd,
+							    const char *name,
+							    int flags,
+							    uint64_t *async_transid,
+							    struct btrfs_util_qgroup_inherit *qgroup_inherit)
+{
+	struct btrfs_ioctl_vol_args_v2 args = {.fd = fd};
+	enum btrfs_util_error err;
+	size_t len;
+	int ret;
+
+	if ((flags & ~BTRFS_UTIL_CREATE_SNAPSHOT_MASK) ||
+	    ((flags & BTRFS_UTIL_CREATE_SNAPSHOT_READ_ONLY) &&
+	     (flags & BTRFS_UTIL_CREATE_SNAPSHOT_RECURSIVE))) {
+		errno = EINVAL;
+		return BTRFS_UTIL_ERROR_INVALID_ARGUMENT;
+	}
+
+	if (flags & BTRFS_UTIL_CREATE_SNAPSHOT_READ_ONLY)
+		args.flags |= BTRFS_SUBVOL_RDONLY;
+	if (async_transid)
+		args.flags |= BTRFS_SUBVOL_CREATE_ASYNC;
+	if (qgroup_inherit) {
+		args.flags |= BTRFS_SUBVOL_QGROUP_INHERIT;
+		args.qgroup_inherit = (struct btrfs_qgroup_inherit *)qgroup_inherit;
+		args.size = (sizeof(*args.qgroup_inherit) +
+			     args.qgroup_inherit->num_qgroups *
+			     sizeof(args.qgroup_inherit->qgroups[0]));
+	}
+
+	len = strlen(name);
+	if (len >= sizeof(args.name)) {
+		errno = ENAMETOOLONG;
+		return BTRFS_UTIL_ERROR_INVALID_ARGUMENT;
+	}
+	memcpy(args.name, name, len);
+	args.name[len] = '\0';
+
+	ret = ioctl(parent_fd, BTRFS_IOC_SNAP_CREATE_V2, &args);
+	if (ret == -1)
+		return BTRFS_UTIL_ERROR_SUBVOL_CREATE_FAILED;
+
+	if (async_transid)
+		*async_transid = args.transid;
+
+	if (flags & BTRFS_UTIL_CREATE_SNAPSHOT_RECURSIVE) {
+		err = snapshot_subvolume_children(fd, parent_fd, name,
+						  async_transid);
+		if (err)
+			return err;
+	}
+
+	return BTRFS_UTIL_OK;
+}
+
 PUBLIC void btrfs_util_destroy_subvolume_iterator(struct btrfs_util_subvolume_iterator *iter)
 {
 	if (iter) {
-- 
2.16.1