include/uapi/linux/cramfs_fs.h

   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 */