1/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
2#ifndef _UAPI__CRAMFS_H
3#define _UAPI__CRAMFS_H
4
5#include <linux/types.h>
6#include <linux/magic.h>
7
8#define CRAMFS_SIGNATURE	"Compressed ROMFS"
9
10/*
11 * Width of various bitfields in struct cramfs_inode.
12 * Primarily used to generate warnings in mkcramfs.
13 */
14#define CRAMFS_MODE_WIDTH 16
15#define CRAMFS_UID_WIDTH 16
16#define CRAMFS_SIZE_WIDTH 24
17#define CRAMFS_GID_WIDTH 8
18#define CRAMFS_NAMELEN_WIDTH 6
19#define CRAMFS_OFFSET_WIDTH 26
20
21/*
22 * Since inode.namelen is a unsigned 6-bit number, the maximum cramfs
23 * path length is 63 << 2 = 252.
24 */
25#define CRAMFS_MAXPATHLEN (((1 << CRAMFS_NAMELEN_WIDTH) - 1) << 2)
26
27/*
28 * Reasonably terse representation of the inode data.
29 */
30struct cramfs_inode {
31	__u32 mode:CRAMFS_MODE_WIDTH, uid:CRAMFS_UID_WIDTH;
32	/* SIZE for device files is i_rdev */
33	__u32 size:CRAMFS_SIZE_WIDTH, gid:CRAMFS_GID_WIDTH;
34	/* NAMELEN is the length of the file name, divided by 4 and
35           rounded up.  (cramfs doesn't support hard links.) */
36	/* OFFSET: For symlinks and non-empty regular files, this
37	   contains the offset (divided by 4) of the file data in
38	   compressed form (starting with an array of block pointers;
39	   see README).  For non-empty directories it is the offset
40	   (divided by 4) of the inode of the first file in that
41	   directory.  For anything else, offset is zero. */
42	__u32 namelen:CRAMFS_NAMELEN_WIDTH, offset:CRAMFS_OFFSET_WIDTH;
43};
44
45struct cramfs_info {
46	__u32 crc;
47	__u32 edition;
48	__u32 blocks;
49	__u32 files;
50};
51
52/*
53 * Superblock information at the beginning of the FS.
54 */
55struct cramfs_super {
56	__u32 magic;			/* 0x28cd3d45 - random number */
57	__u32 size;			/* length in bytes */
58	__u32 flags;			/* feature flags */
59	__u32 future;			/* reserved for future use */
60	__u8 signature[16];		/* "Compressed ROMFS" */
61	struct cramfs_info fsid;	/* unique filesystem info */
62	__u8 name[16];			/* user-defined name */
63	struct cramfs_inode root;	/* root inode data */
64};
65
66/*
67 * Feature flags
68 *
69 * 0x00000000 - 0x000000ff: features that work for all past kernels
70 * 0x00000100 - 0xffffffff: features that don't work for past kernels
71 */
72#define CRAMFS_FLAG_FSID_VERSION_2	0x00000001	/* fsid version #2 */
73#define CRAMFS_FLAG_SORTED_DIRS		0x00000002	/* sorted dirs */
74#define CRAMFS_FLAG_HOLES		0x00000100	/* support for holes */
75#define CRAMFS_FLAG_WRONG_SIGNATURE	0x00000200	/* reserved */
76#define CRAMFS_FLAG_SHIFTED_ROOT_OFFSET	0x00000400	/* shifted root fs */
77#define CRAMFS_FLAG_EXT_BLOCK_POINTERS	0x00000800	/* block pointer extensions */
78
79/*
80 * Valid values in super.flags.  Currently we refuse to mount
81 * if (flags & ~CRAMFS_SUPPORTED_FLAGS).  Maybe that should be
82 * changed to test super.future instead.
83 */
84#define CRAMFS_SUPPORTED_FLAGS	( 0x000000ff \
85				| CRAMFS_FLAG_HOLES \
86				| CRAMFS_FLAG_WRONG_SIGNATURE \
87				| CRAMFS_FLAG_SHIFTED_ROOT_OFFSET \
88				| CRAMFS_FLAG_EXT_BLOCK_POINTERS )
89
90/*
91 * Block pointer flags
92 *
93 * The maximum block offset that needs to be represented is roughly:
94 *
95 *   (1 << CRAMFS_OFFSET_WIDTH) * 4 +
96 *   (1 << CRAMFS_SIZE_WIDTH) / PAGE_SIZE * (4 + PAGE_SIZE)
97 *   = 0x11004000
98 *
99 * That leaves room for 3 flag bits in the block pointer table.
100 */
101#define CRAMFS_BLK_FLAG_UNCOMPRESSED	(1 << 31)
102#define CRAMFS_BLK_FLAG_DIRECT_PTR	(1 << 30)
103
104#define CRAMFS_BLK_FLAGS	( CRAMFS_BLK_FLAG_UNCOMPRESSED \
105				| CRAMFS_BLK_FLAG_DIRECT_PTR )
106
107/*
108 * Direct blocks are at least 4-byte aligned.
109 * Pointers to direct blocks are shifted down by 2 bits.
110 */
111#define CRAMFS_BLK_DIRECT_PTR_SHIFT	2
112
113#endif /* _UAPI__CRAMFS_H */
114