cramfs_fs.h

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#ifndef _UAPI__CRAMFS_H
#define _UAPI__CRAMFS_H

#include <linux/types.h>
#include <linux/magic.h>

#define CRAMFS_SIGNATURE    "Compressed ROMFS"

/*
 * Width of various bitfields in struct cramfs_inode.
 * Primarily used to generate warnings in mkcramfs.
 */
#define CRAMFS_MODE_WIDTH 16
#define CRAMFS_UID_WIDTH 16
#define CRAMFS_SIZE_WIDTH 24
#define CRAMFS_GID_WIDTH 8
#define CRAMFS_NAMELEN_WIDTH 6
#define CRAMFS_OFFSET_WIDTH 26

/*
 * Since inode.namelen is a unsigned 6-bit number, the maximum cramfs
 * path length is 63 << 2 = 252.
 */
#define CRAMFS_MAXPATHLEN (((1 << CRAMFS_NAMELEN_WIDTH) - 1) << 2)

/*
 * Reasonably terse representation of the inode data.
 */
struct cramfs_inode {
    __u32 mode:CRAMFS_MODE_WIDTH, uid:CRAMFS_UID_WIDTH;
    /* SIZE for device files is i_rdev */
    __u32 size:CRAMFS_SIZE_WIDTH, gid:CRAMFS_GID_WIDTH;
    /* NAMELEN is the length of the file name, divided by 4 and
           rounded up.  (cramfs doesn't support hard links.) */
    /* OFFSET: For symlinks and non-empty regular files, this
       contains the offset (divided by 4) of the file data in
       compressed form (starting with an array of block pointers;
       see README).  For non-empty directories it is the offset
       (divided by 4) of the inode of the first file in that
       directory.  For anything else, offset is zero. */
    __u32 namelen:CRAMFS_NAMELEN_WIDTH, offset:CRAMFS_OFFSET_WIDTH;
};

struct cramfs_info {
    __u32 crc;
    __u32 edition;
    __u32 blocks;
    __u32 files;
};

/*
 * Superblock information at the beginning of the FS.
 */
struct cramfs_super {
    __u32 magic;            /* 0x28cd3d45 - random number */
    __u32 size;         /* length in bytes */
    __u32 flags;            /* feature flags */
    __u32 future;           /* reserved for future use */
    __u8 signature[16];     /* "Compressed ROMFS" */
    struct cramfs_info fsid;    /* unique filesystem info */
    __u8 name[16];          /* user-defined name */
    struct cramfs_inode root;   /* root inode data */
};

/*
 * Feature flags
 *
 * 0x00000000 - 0x000000ff: features that work for all past kernels
 * 0x00000100 - 0xffffffff: features that don't work for past kernels
 */
#define CRAMFS_FLAG_FSID_VERSION_2  0x00000001  /* fsid version #2 */
#define CRAMFS_FLAG_SORTED_DIRS     0x00000002  /* sorted dirs */
#define CRAMFS_FLAG_HOLES       0x00000100  /* support for holes */
#define CRAMFS_FLAG_WRONG_SIGNATURE 0x00000200  /* reserved */
#define CRAMFS_FLAG_SHIFTED_ROOT_OFFSET 0x00000400  /* shifted root fs */

/*
 * Valid values in super.flags.  Currently we refuse to mount
 * if (flags & ~CRAMFS_SUPPORTED_FLAGS).  Maybe that should be
 * changed to test super.future instead.
 */
#define CRAMFS_SUPPORTED_FLAGS  ( 0x000000ff \
                | CRAMFS_FLAG_HOLES \
                | CRAMFS_FLAG_WRONG_SIGNATURE \
                | CRAMFS_FLAG_SHIFTED_ROOT_OFFSET )


#endif /* _UAPI__CRAMFS_H */