btrfs: Introduce BTRFS engine

It is been found that BTRFS uses per subvolume device
numbering scheme  which causes some of our tests to fail
if they are laying on this filesystem.

Here we introduce minimal engine which parses subvolumes
present on mount point.

The interface is two functions

 - btrfs_parse_mountinfo: this one parses subvolume and caches the results
 - is_btrfs_subvol: test if device id is laying on subvolume

In the code we assume that cpu we're running on
is little endian, thus if one day we run on big
ending machine the code must be updated accordingly.
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

Makefile.crtools

@@ -39,6 +39,7 @@ obj-y	+= shmem.o
 obj-y	+= eventfd.o
 obj-y	+= eventpoll.o
 obj-y	+= mount.o
+obj-y	+= mount-btrfs.o
 obj-y	+= fsnotify.o
 obj-y	+= signalfd.o
 obj-y	+= pstree.o

include/mount-btrfs.h

+#ifndef __CR_BTRFS_H__
+#define __CR_BTRFS_H__
+
+#include <asm/types.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+
+#include <linux/ioctl.h>
+
+#include "asm/int.h"
+#include "compiler.h"
+#include "rbtree.h"
+
+struct mount_info;
+
+#define BTRFS_IOCTL_MAGIC		0x94
+#define BTRFS_VOL_NAME_MAX		255
+
+struct btrfs_root_ref {
+	u64 dirid;
+	u64 sequence;
+	u16 name_len;
+} __packed;
+
+#define BTRFS_ROOT_ITEM_KEY		132
+#define BTRFS_ROOT_BACKREF_KEY		144
+#define BTRFS_FS_TREE_OBJECTID		5ULL
+
+#define BTRFS_FIRST_FREE_OBJECTID	256ULL
+#define BTRFS_LAST_FREE_OBJECTID	-256ULL
+
+#define BTRFS_INO_LOOKUP_PATH_MAX	4080
+struct btrfs_ioctl_ino_lookup_args {
+	u64				treeid;
+	u64				objectid;
+	char				name[BTRFS_INO_LOOKUP_PATH_MAX];
+};
+
+struct btrfs_ioctl_search_header {
+	u64				transid;
+	u64				objectid;
+	u64				offset;
+	u32				type;
+	u32				len;
+};
+
+struct btrfs_ioctl_search_key {
+	u64				tree_id;
+	u64				min_objectid;
+	u64				max_objectid;
+	u64				min_offset;
+	u64				max_offset;
+	u64				min_transid;
+	u64				max_transid;
+	u32				min_type;
+	u32				max_type;
+	u32				nr_items;
+	u32				unused;
+	u64				unused1;
+	u64				unused2;
+	u64				unused3;
+	u64				unused4;
+};
+
+#define BTRFS_SEARCH_ARGS_BUFSIZE (4096 - sizeof(struct btrfs_ioctl_search_key))
+
+struct btrfs_ioctl_search_args {
+	struct btrfs_ioctl_search_key	key;
+	char				buf[BTRFS_SEARCH_ARGS_BUFSIZE];
+};
+
+#define BTRFS_IOC_TREE_SEARCH		\
+	_IOWR(BTRFS_IOCTL_MAGIC, 17, struct btrfs_ioctl_search_args)
+
+#define BTRFS_IOC_INO_LOOKUP		\
+	_IOWR(BTRFS_IOCTL_MAGIC, 18, struct btrfs_ioctl_ino_lookup_args)
+
+extern int btrfs_parse_mountinfo(struct mount_info *m);
+extern bool is_btrfs_subvol(dev_t vol_id, dev_t dev_id);
+
+#endif /* __CR_BTRFS_H__ */