uapi/linux/cramfs_fs.h

0001 /* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
0002 #ifndef _UAPI__CRAMFS_H
0003 #define _UAPI__CRAMFS_H
0004
0005 #include <linux/types.h>
0006 #include <linux/magic.h>
0007
0008 #define CRAMFS_SIGNATURE    "Compressed ROMFS"
0009
0010 /*
0011  * Width of various bitfields in struct cramfs_inode.
0012  * Primarily used to generate warnings in mkcramfs.
0013  */
0014 #define CRAMFS_MODE_WIDTH 16
0015 #define CRAMFS_UID_WIDTH 16
0016 #define CRAMFS_SIZE_WIDTH 24
0017 #define CRAMFS_GID_WIDTH 8
0018 #define CRAMFS_NAMELEN_WIDTH 6
0019 #define CRAMFS_OFFSET_WIDTH 26
0020
0021 /*
0022  * Since inode.namelen is a unsigned 6-bit number, the maximum cramfs
0023  * path length is 63 << 2 = 252.
0024  */
0025 #define CRAMFS_MAXPATHLEN (((1 << CRAMFS_NAMELEN_WIDTH) - 1) << 2)
0026
0027 /*
0028  * Reasonably terse representation of the inode data.
0029  */
0030 struct cramfs_inode {
0031     __u32 mode:CRAMFS_MODE_WIDTH, uid:CRAMFS_UID_WIDTH;
0032     /* SIZE for device files is i_rdev */
0033     __u32 size:CRAMFS_SIZE_WIDTH, gid:CRAMFS_GID_WIDTH;
0034     /* NAMELEN is the length of the file name, divided by 4 and
0035            rounded up.  (cramfs doesn't support hard links.) */
0036     /* OFFSET: For symlinks and non-empty regular files, this
0037        contains the offset (divided by 4) of the file data in
0038        compressed form (starting with an array of block pointers;
0039        see README).  For non-empty directories it is the offset
0040        (divided by 4) of the inode of the first file in that
0041        directory.  For anything else, offset is zero. */
0042     __u32 namelen:CRAMFS_NAMELEN_WIDTH, offset:CRAMFS_OFFSET_WIDTH;
0043 };
0044
0045 struct cramfs_info {
0046     __u32 crc;
0047     __u32 edition;
0048     __u32 blocks;
0049     __u32 files;
0050 };
0051
0052 /*
0053  * Superblock information at the beginning of the FS.
0054  */
0055 struct cramfs_super {
0056     __u32 magic;            /* 0x28cd3d45 - random number */
0057     __u32 size;         /* length in bytes */
0058     __u32 flags;            /* feature flags */
0059     __u32 future;           /* reserved for future use */
0060     __u8 signature[16];     /* "Compressed ROMFS" */
0061     struct cramfs_info fsid;    /* unique filesystem info */
0062     __u8 name[16];          /* user-defined name */
0063     struct cramfs_inode root;   /* root inode data */
0064 };
0065
0066 /*
0067  * Feature flags
0068  *
0069  * 0x00000000 - 0x000000ff: features that work for all past kernels
0070  * 0x00000100 - 0xffffffff: features that don't work for past kernels
0071  */
0072 #define CRAMFS_FLAG_FSID_VERSION_2  0x00000001  /* fsid version #2 */
0073 #define CRAMFS_FLAG_SORTED_DIRS     0x00000002  /* sorted dirs */
0074 #define CRAMFS_FLAG_HOLES       0x00000100  /* support for holes */
0075 #define CRAMFS_FLAG_WRONG_SIGNATURE 0x00000200  /* reserved */
0076 #define CRAMFS_FLAG_SHIFTED_ROOT_OFFSET 0x00000400  /* shifted root fs */
0077 #define CRAMFS_FLAG_EXT_BLOCK_POINTERS  0x00000800  /* block pointer extensions */
0078
0079 /*
0080  * Valid values in super.flags.  Currently we refuse to mount
0081  * if (flags & ~CRAMFS_SUPPORTED_FLAGS).  Maybe that should be
0082  * changed to test super.future instead.
0083  */
0084 #define CRAMFS_SUPPORTED_FLAGS  ( 0x000000ff \
0085                 | CRAMFS_FLAG_HOLES \
0086                 | CRAMFS_FLAG_WRONG_SIGNATURE \
0087                 | CRAMFS_FLAG_SHIFTED_ROOT_OFFSET \
0088                 | CRAMFS_FLAG_EXT_BLOCK_POINTERS )
0089
0090 /*
0091  * Block pointer flags
0092  *
0093  * The maximum block offset that needs to be represented is roughly:
0094  *
0095  *   (1 << CRAMFS_OFFSET_WIDTH) * 4 +
0096  *   (1 << CRAMFS_SIZE_WIDTH) / PAGE_SIZE * (4 + PAGE_SIZE)
0097  *   = 0x11004000
0098  *
0099  * That leaves room for 3 flag bits in the block pointer table.
0100  */
0101 #define CRAMFS_BLK_FLAG_UNCOMPRESSED    (1 << 31)
0102 #define CRAMFS_BLK_FLAG_DIRECT_PTR  (1 << 30)
0103
0104 #define CRAMFS_BLK_FLAGS    ( CRAMFS_BLK_FLAG_UNCOMPRESSED \
0105                 | CRAMFS_BLK_FLAG_DIRECT_PTR )
0106
0107 /*
0108  * Direct blocks are at least 4-byte aligned.
0109  * Pointers to direct blocks are shifted down by 2 bits.
0110  */
0111 #define CRAMFS_BLK_DIRECT_PTR_SHIFT 2
0112
0113 #endif /* _UAPI__CRAMFS_H */