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-
- Cramfs - cram a filesystem onto a small ROM
-
-cramfs is designed to be simple and small, and to compress things well.
-
-It uses the zlib routines to compress a file one page at a time, and
-allows random page access. The meta-data is not compressed, but is
-expressed in a very terse representation to make it use much less
-diskspace than traditional filesystems.
-
-You can't write to a cramfs filesystem (making it compressible and
-compact also makes it _very_ hard to update on-the-fly), so you have to
-create the disk image with the "mkcramfs" utility.
-
-
-Usage Notes
------------
-
-File sizes are limited to less than 16MB.
-
-Maximum filesystem size is a little over 256MB. (The last file on the
-filesystem is allowed to extend past 256MB.)
-
-Only the low 8 bits of gid are stored. The current version of
-mkcramfs simply truncates to 8 bits, which is a potential security
-issue.
-
-Hard links are supported, but hard linked files
-will still have a link count of 1 in the cramfs image.
-
-Cramfs directories have no `.' or `..' entries. Directories (like
-every other file on cramfs) always have a link count of 1. (There's
-no need to use -noleaf in `find', btw.)
-
-No timestamps are stored in a cramfs, so these default to the epoch
-(1970 GMT). Recently-accessed files may have updated timestamps, but
-the update lasts only as long as the inode is cached in memory, after
-which the timestamp reverts to 1970, i.e. moves backwards in time.
-
-Currently, cramfs must be written and read with architectures of the
-same endianness, and can be read only by kernels with PAGE_CACHE_SIZE
-== 4096. At least the latter of these is a bug, but it hasn't been
-decided what the best fix is. For the moment if you have larger pages
-you can just change the #define in mkcramfs.c, so long as you don't
-mind the filesystem becoming unreadable to future kernels.
-
-
-For /usr/share/magic
---------------------
-
-0 ulelong 0x28cd3d45 Linux cramfs offset 0
->4 ulelong x size %d
->8 ulelong x flags 0x%x
->12 ulelong x future 0x%x
->16 string >\0 signature "%.16s"
->32 ulelong x fsid.crc 0x%x
->36 ulelong x fsid.edition %d
->40 ulelong x fsid.blocks %d
->44 ulelong x fsid.files %d
->48 string >\0 name "%.16s"
-512 ulelong 0x28cd3d45 Linux cramfs offset 512
->516 ulelong x size %d
->520 ulelong x flags 0x%x
->524 ulelong x future 0x%x
->528 string >\0 signature "%.16s"
->544 ulelong x fsid.crc 0x%x
->548 ulelong x fsid.edition %d
->552 ulelong x fsid.blocks %d
->556 ulelong x fsid.files %d
->560 string >\0 name "%.16s"
-
-
-Hacker Notes
-------------
-
-See fs/cramfs/README for filesystem layout and implementation notes.