diff options
Diffstat (limited to 'Documentation/filesystems')
| -rw-r--r-- | Documentation/filesystems/index.rst | 1 | ||||
| -rw-r--r-- | Documentation/filesystems/romfs.rst (renamed from Documentation/filesystems/romfs.txt) | 42 |
2 files changed, 26 insertions, 17 deletions
diff --git a/Documentation/filesystems/index.rst b/Documentation/filesystems/index.rst index 0aade8146d4d..3b26639517af 100644 --- a/Documentation/filesystems/index.rst +++ b/Documentation/filesystems/index.rst @@ -85,5 +85,6 @@ Documentation for filesystem implementations. qnx6 ramfs-rootfs-initramfs relay + romfs virtiofs vfat diff --git a/Documentation/filesystems/romfs.txt b/Documentation/filesystems/romfs.rst index e2b07cc9120a..465b11efa9be 100644 --- a/Documentation/filesystems/romfs.txt +++ b/Documentation/filesystems/romfs.rst @@ -1,4 +1,8 @@ -ROMFS - ROM FILE SYSTEM +.. SPDX-License-Identifier: GPL-2.0 + +======================= +ROMFS - ROM File System +======================= This is a quite dumb, read only filesystem, mainly for initial RAM disks of installation disks. It has grown up by the need of having @@ -51,9 +55,9 @@ the 16 byte padding for the name and the contents, also 16+14+15 = 45 bytes. This is quite rare however, since most file names are longer than 3 bytes, and shorter than 15 bytes. -The layout of the filesystem is the following: +The layout of the filesystem is the following:: -offset content + offset content +---+---+---+---+ 0 | - | r | o | m | \ @@ -84,9 +88,9 @@ the source. This algorithm was chosen because although it's not quite reliable, it does not require any tables, and it is very simple. The following bytes are now part of the file system; each file header -must begin on a 16 byte boundary. +must begin on a 16 byte boundary:: -offset content + offset content +---+---+---+---+ 0 | next filehdr|X| The offset of the next file header @@ -114,7 +118,9 @@ file is user and group 0, this should never be a problem for the intended use. The mapping of the 8 possible values to file types is the following: +== =============== ============================================ mapping spec.info means +== =============== ============================================ 0 hard link link destination [file header] 1 directory first file's header 2 regular file unused, must be zero [MBZ] @@ -123,6 +129,7 @@ the following: 5 char device - " - 6 socket unused, MBZ 7 fifo unused, MBZ +== =============== ============================================ Note that hard links are specifically marked in this filesystem, but they will behave as you can expect (i.e. share the inode number). @@ -158,24 +165,24 @@ to romfs-subscribe@shadow.banki.hu, the content is irrelevant. Pending issues: - Permissions and owner information are pretty essential features of a -Un*x like system, but romfs does not provide the full possibilities. -I have never found this limiting, but others might. + Un*x like system, but romfs does not provide the full possibilities. + I have never found this limiting, but others might. - The file system is read only, so it can be very small, but in case -one would want to write _anything_ to a file system, he still needs -a writable file system, thus negating the size advantages. Possible -solutions: implement write access as a compile-time option, or a new, -similarly small writable filesystem for RAM disks. + one would want to write _anything_ to a file system, he still needs + a writable file system, thus negating the size advantages. Possible + solutions: implement write access as a compile-time option, or a new, + similarly small writable filesystem for RAM disks. - Since the files are only required to have alignment on a 16 byte -boundary, it is currently possibly suboptimal to read or execute files -from the filesystem. It might be resolved by reordering file data to -have most of it (i.e. except the start and the end) laying at "natural" -boundaries, thus it would be possible to directly map a big portion of -the file contents to the mm subsystem. + boundary, it is currently possibly suboptimal to read or execute files + from the filesystem. It might be resolved by reordering file data to + have most of it (i.e. except the start and the end) laying at "natural" + boundaries, thus it would be possible to directly map a big portion of + the file contents to the mm subsystem. - Compression might be an useful feature, but memory is quite a -limiting factor in my eyes. + limiting factor in my eyes. - Where it is used? @@ -183,4 +190,5 @@ limiting factor in my eyes. Have fun, + Janos Farkas <chexum@shadow.banki.hu> |