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Diffstat (limited to 'Documentation/filesystems/cramfs.rst')
| -rw-r--r-- | Documentation/filesystems/cramfs.rst | 22 |
1 files changed, 14 insertions, 8 deletions
diff --git a/Documentation/filesystems/cramfs.rst b/Documentation/filesystems/cramfs.rst index afbdbde98bd2..221c0bf91b9c 100644 --- a/Documentation/filesystems/cramfs.rst +++ b/Documentation/filesystems/cramfs.rst @@ -28,8 +28,10 @@ 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. +Hard links are not preserved. mkcramfs deduplicates files with +identical content, but two names for the same on-disk inode in the +source tree become two separate (content-shared) entries in the +image, and cramfs always reports a link count of 1. Cramfs directories have no ``.`` or ``..`` entries. Directories (like every other file on cramfs) always have a link count of 1. (There's @@ -40,12 +42,16 @@ No timestamps are stored in a cramfs, so these default to the epoch 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_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. +The on-disk layout is host-endian: the kernel does not swab, and +refuses to mount an image whose endianness does not match the CPU. +For cross-builds, mkcramfs -B / -L forces the output endianness so +that a host of one endianness can produce an image for a target of +the other. + +The on-disk block size is fixed at 4096 bytes. On systems with a +larger PAGE_SIZE you can change the #define in mkcramfs.c, with the +caveat that the resulting image will only be readable on kernels +configured for the same PAGE_SIZE. Memory Mapped cramfs image |