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 */
30 struct 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
45 struct 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 */
55 struct 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 */