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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.