patch-2.3.40 linux/Documentation/filesystems/cramfs.txt

• Lines: 44
• Date: Tue Jan 11 10:24:58 2000
• Orig file: v2.3.39/linux/Documentation/filesystems/cramfs.txt
• Orig date: Wed Dec 29 13:13:12 1999

diff -u --recursive --new-file v2.3.39/linux/Documentation/filesystems/cramfs.txt linux/Documentation/filesystems/cramfs.txt
@@ -11,3 +11,43 @@
 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 in scripts/cramfs.
+
+
+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.)  (Comments in mkcramfs.c
+suggest that ROM sizes may be limited to 64MB, though that's not a
+limitation in cramfs code.)
+
+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 not supported, but symlinks are.  (See also the TODO
+comment in mkcramfs.c at the nlink test.)
+
+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.
+
+
+Hacker Notes
+------------
+
+See fs/cramfs/README for filesystem layout and implementation notes.