fs: btrfs: Add disk-to-cpu and cpu-to-disk conversion functions

BTRFS on disk structures are stored in Little Endian. Add functions
to convert this structures to cpu and to disk format.

On Little Endian hosts, these functions do nothing.

On Big Endian the CALL_MACRO_FROM_EACH from variadic-macro.h is used
to define all the members for each structure on which cpu_to_le* or
le*_to_cpu is to be called.

Signed-off-by: Marek Behun <marek.behun@nic.cz>

 create mode 100644 fs/btrfs/conv-funcs.h

fs/btrfs/conv-funcs.h

@@ -0,0 +1,176 @@
+/*
+ * Functions to convert BTRFS structures from disk to CPU endianness and back.
+ *
+ * 2017 Marek Behun, CZ.NIC, marek.behun@nic.cz
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#ifndef __BTRFS_CONV_FUNCS_H__
+#define __BTRFS_CONV_FUNCS_H__
+
+#include "ctree.h"
+#include <u-boot/variadic-macro.h>
+#include <asm/byteorder.h>
+
+/* We are using variadic macros and C11 _Generic to achieve compact code.
+
+   We want to define macro DEFINE_CONV(x, ...), where the first argument is the
+   name of the structure for which it shall define conversion functions (the
+   names of the functions shall be x_to_cpu and x_to_disk), and the other
+   arguments are names of the members on which the functions shall do
+   endianness conversion. */
+
+#if defined(__LITTLE_ENDIAN)
+
+/* If the target machine is little endian, the conversion functions do
+   nothing, since the on disk format is little endian. */
+
+# define DEFINE_CONV(n,...)					\
+	static inline struct n *n##_to_disk(struct n * r)	\
+	{							\
+		return r;					\
+	}							\
+	static inline struct n *n##_to_cpu(struct n * r)	\
+	{							\
+		return r;					\
+	}
+
+# define DEFINE_CONV_ALT(n,a,...)				\
+	static inline struct n *n##_to_disk_##a(struct n * r)	\
+	{							\
+		return r;					\
+	}							\
+	static inline struct n *n##_to_cpu_##a(struct n * r)	\
+	{							\
+		return r;					\
+	}
+
+#else /* !defined(__LITTLE_ENDIAN) */
+
+/* Some structures contain not only scalar members, but compound types as well
+   (for example, struct btrfs_inode_item contains members of type struct
+   btrfs_timespec.
+
+   For these members we want to call the conversion function recursively, so
+   first we declare the functions taking pointers to this types (these function
+   will be defined later by the DEFINE_CONV macro) and then we define
+   correspond functions taking non-pointers, so that they can be used in the
+   expansion of the _Generic. */
+# define DEFINE_CONV_FOR_STRUCT(n)				\
+	static inline struct n * n##_to_disk(struct n *);	\
+	static inline struct n * n##_to_cpu(struct n *);	\
+	static inline struct n n##_to_disk_v(struct n x) {	\
+		return *n##_to_disk(&x);			\
+	}							\
+	static inline struct n n##_to_cpu_v(struct n x) {	\
+		return *n##_to_cpu(&x);				\
+	}
+
+DEFINE_CONV_FOR_STRUCT(btrfs_key)
+DEFINE_CONV_FOR_STRUCT(btrfs_stripe)
+DEFINE_CONV_FOR_STRUCT(btrfs_timespec)
+DEFINE_CONV_FOR_STRUCT(btrfs_inode_item)
+DEFINE_CONV_FOR_STRUCT(btrfs_root_backup)
+DEFINE_CONV_FOR_STRUCT(btrfs_dev_item)
+
+/* Now define the _Generic for both CPU to LE and LE to CPU */
+# define DEFINE_CONV_CPU_TO_LE(x)					\
+	(d->x) = _Generic((d->x),					\
+		__u16: cpu_to_le16,					\
+		__u32: cpu_to_le32,					\
+		__u64: cpu_to_le64,					\
+		struct btrfs_key: btrfs_key_to_disk_v,			\
+		struct btrfs_stripe: btrfs_stripe_to_disk_v,		\
+		struct btrfs_timespec: btrfs_timespec_to_disk_v,	\
+		struct btrfs_inode_item: btrfs_inode_item_to_disk_v,	\
+		struct btrfs_root_backup: btrfs_root_backup_to_disk_v,	\
+		struct btrfs_dev_item: btrfs_dev_item_to_disk_v		\
+		)((d->x));
+
+# define DEFINE_CONV_LE_TO_CPU(x)					\
+	(d->x) = _Generic((d->x),					\
+		__u16: le16_to_cpu,					\
+		__u32: le32_to_cpu,					\
+		__u64: le64_to_cpu,					\
+		struct btrfs_key: btrfs_key_to_cpu_v,			\
+		struct btrfs_stripe: btrfs_stripe_to_cpu_v,		\
+		struct btrfs_timespec: btrfs_timespec_to_cpu_v,		\
+		struct btrfs_inode_item: btrfs_inode_item_to_cpu_v,	\
+		struct btrfs_root_backup: btrfs_root_backup_to_cpu_v,	\
+		struct btrfs_dev_item: btrfs_dev_item_to_cpu_v		\
+		)((d->x));
+
+# define DEFINE_CONV_ONE(t,n,m,...)			\
+	static inline struct t * n(struct t * d) {	\
+		CALL_MACRO_FOR_EACH(m, ##__VA_ARGS__)	\
+		return d;				\
+	}
+
+/* Finally define the DEFINE_CONV macro */
+# define DEFINE_CONV(n,...) \
+	DEFINE_CONV_ONE(n,n##_to_disk,DEFINE_CONV_CPU_TO_LE,##__VA_ARGS__) \
+	DEFINE_CONV_ONE(n,n##_to_cpu,DEFINE_CONV_LE_TO_CPU,##__VA_ARGS__)
+
+# define DEFINE_CONV_ALT(n,a,...) \
+	DEFINE_CONV_ONE(n,n##_to_disk_##a,DEFINE_CONV_CPU_TO_LE, \
+		##__VA_ARGS__) \
+	DEFINE_CONV_ONE(n,n##_to_cpu_##a,DEFINE_CONV_LE_TO_CPU,##__VA_ARGS__)
+
+#endif /* !defined(__LITTLE_ENDIAN) */
+
+DEFINE_CONV(btrfs_key, objectid, offset)
+DEFINE_CONV(btrfs_dev_item, devid, total_bytes, bytes_used, io_align, io_width,
+	    sector_size, type, generation, start_offset, dev_group)
+DEFINE_CONV(btrfs_stripe, devid, offset)
+DEFINE_CONV(btrfs_chunk, length, owner, stripe_len, type, io_align, io_width,
+	    sector_size, num_stripes, sub_stripes)
+DEFINE_CONV(btrfs_free_space_entry, offset, bytes)
+DEFINE_CONV(btrfs_free_space_header, location, generation, num_entries,
+	    num_bitmaps)
+DEFINE_CONV(btrfs_extent_item, refs, generation, flags)
+DEFINE_CONV(btrfs_tree_block_info, key)
+DEFINE_CONV(btrfs_extent_data_ref, root, objectid, offset, count)
+DEFINE_CONV(btrfs_shared_data_ref, count)
+DEFINE_CONV(btrfs_extent_inline_ref, offset)
+DEFINE_CONV(btrfs_dev_extent, chunk_tree, chunk_objectid, chunk_offset, length)
+DEFINE_CONV(btrfs_inode_ref, index, name_len)
+DEFINE_CONV(btrfs_inode_extref, parent_objectid, index, name_len)
+DEFINE_CONV(btrfs_timespec, sec, nsec)
+DEFINE_CONV(btrfs_inode_item, generation, transid, size, nbytes, block_group,
+	    nlink, uid, gid, mode, rdev, flags, sequence, atime, ctime, mtime,
+	    otime)
+DEFINE_CONV(btrfs_dir_log_item, end)
+DEFINE_CONV(btrfs_dir_item, location, transid, data_len, name_len)
+DEFINE_CONV(btrfs_root_item, inode, generation, root_dirid, bytenr, byte_limit,
+	    bytes_used, last_snapshot, flags, refs, drop_progress,
+	    generation_v2, ctransid, otransid, stransid, rtransid, ctime,
+	    otime, stime, rtime)
+DEFINE_CONV(btrfs_root_ref, dirid, sequence, name_len)
+DEFINE_CONV(btrfs_file_extent_item, generation, ram_bytes, other_encoding,
+	    disk_bytenr, disk_num_bytes, offset, num_bytes)
+DEFINE_CONV_ALT(btrfs_file_extent_item, inl, generation, ram_bytes,
+		other_encoding)
+DEFINE_CONV(btrfs_dev_replace_item, src_devid, cursor_left, cursor_right,
+	    cont_reading_from_srcdev_mode, replace_state, time_started,
+	    time_stopped, num_write_errors, num_uncorrectable_read_errors)
+DEFINE_CONV(btrfs_block_group_item, used, chunk_objectid, flags)
+DEFINE_CONV(btrfs_free_space_info, extent_count, flags)
+
+DEFINE_CONV(btrfs_header, bytenr, flags, generation, owner, nritems)
+DEFINE_CONV(btrfs_root_backup, tree_root, tree_root_gen, chunk_root,
+	    chunk_root_gen, extent_root, extent_root_gen, fs_root, fs_root_gen,
+	    dev_root, dev_root_gen, csum_root, csum_root_gen, total_bytes,
+	    bytes_used, num_devices)
+DEFINE_CONV(btrfs_super_block, bytenr, flags, magic, generation, root,
+	    chunk_root, log_root, log_root_transid, total_bytes, bytes_used,
+	    root_dir_objectid, num_devices, sectorsize, nodesize,
+	    __unused_leafsize, stripesize, sys_chunk_array_size,
+	    chunk_root_generation, compat_flags, compat_ro_flags,
+	    incompat_flags, csum_type, dev_item, cache_generation,
+	    uuid_tree_generation, super_roots[0], super_roots[1], 
+	    super_roots[2], super_roots[3])
+DEFINE_CONV(btrfs_item, key, offset, size)
+DEFINE_CONV(btrfs_key_ptr, key, blockptr, generation)
+
+#endif /* __BTRFS_CONV_FUNCS_H__ */