README
1$OpenBSD: README,v 1.4 2022/01/11 05:34:32 jsg Exp $
2$NetBSD: README,v 1.7 2015/01/12 19:50:47 christos Exp $
3
4makefs - build a file system image from a directory tree
5
6NOTES:
7
8 * This tool uses modified local copies of source found in other
9 parts of the tree. This is intentional.
10
11 * makefs is a work in progress, and subject to change.
12
13
14user overview:
15--------------
16
17makefs creates a file system image from a given directory tree.
18the following file system types can be built:
19
20 cd9660 ISO 9660 file system
21 ffs BSD fast file system
22 msdos MS-DOS `FAT' file system (FAT12, FAT16, FAT32)
23
24Various file system independent parameters and constraints can be
25specified, such as:
26
27 - minimum file system size (in KB)
28 - maximum file system size (in KB)
29 - free inodes
30 - free blocks (in KB)
31 - file containing list of files to specifically exclude or include
32 - fnmatch(3) pattern of filenames to exclude or include
33 - endianness of target file system
34
35File system specific parameters can be given as well, with a command
36line option such as "-o fsspeccific-options,comma-separated".
37For example, ffs would allow tuning of:
38
39 - block & fragment size
40 - cylinder groups
41 - number of blocks per inode
42 - minimum free space
43
44Other file systems might have controls on how to "munge" file names to
45fit within the constraints of the target file system.
46
47Exit codes:
48 0 all ok
49 1 fatal error
50 2 some files couldn't be added during image creation
51 (bad perms, missing file, etc). image will continue
52 to be made
53
54
55Implementation overview:
56------------------------
57
58The implementation must allow for easy addition of extra file systems
59with minimal changes to the file system independent sections.
60
61The main program will:
62 - parse the options, including calling fs-specific routines to
63 validate fs-specific options
64 - walk the tree, building up a data structure which represents
65 the tree to stuff into the image. The structure will
66 probably be a similar tree to what mtree(8) uses internally;
67 a linked list of entries per directory with a child pointer
68 to children of directories. ".." won't be stored in the list;
69 the fs-specific tree walker should add this if required by the fs.
70 this builder have the smarts to handle hard links correctly.
71 - Call an fs-specific routine to build the image based on the
72 data structures.
73
74Each fs-specific module should have the following external interfaces:
75
76 prepare_options optional file system specific defaults that need to be
77 setup before parsing fs-specific options.
78
79 parse_options parse the string for fs-specific options, feeding
80 errors back to the user as appropriate
81
82 cleanup_options optional file system specific data that need to be
83 cleaned up when done with this filesystem.
84
85 make_fs take the data structures representing the
86 directory tree and fs parameters,
87 validate that the parameters are valid
88 (e.g, the requested image will be large enough),
89 create the image, and
90 populate the image
91
92prepare_options and cleanup_options are optional and can be NULL.
93
94NOTE: All file system specific options are referenced via the fs_specific
95pointer from the fsinfo_t structure. It is up to the filesystem to allocate
96and free any data needed for this via the prepare and cleanup callbacks.
97
98Each fs-specific module will need to add its routines to the dispatch array
99in makefs.c and add prototypes for these to makefs.h
100
101All other implementation details should not need to change any of the
102generic code.
103
104ffs implementation
105------------------
106
107In the ffs case, we can leverage off sbin/newfs/mkfs.c to actually build
108the image. When building and populating the image, the implementation
109can be greatly simplified if some assumptions are made:
110 - the total required size (in blocks and inodes) is determined
111 as part of the validation phase
112 - a "file" (including a directory) has a known size, so
113 support for growing a file is not necessary
114
115Two underlying primitives are provided:
116 make_inode create an inode, returning the inode number
117
118 write_file write file (from memory if DIR, file descriptor
119 if FILE or SYMLINK), referencing given inode.
120 it is smart enough to know if a short symlink
121 can be stuffed into the inode, etc.
122
123When creating a directory, the directory entries in the previously
124built tree data structure is scanned and built in memory so it can
125be written entirely as a single write_file() operation.
126