1 $NetBSD: README,v 1.7 2015/01/12 19:50:47 christos Exp $
3 makefs - build a file system image from a directory tree
7 * This tool uses modified local copies of source found in other
8 parts of the tree. This is intentional.
10 * makefs is a work in progress, and subject to change.
16 makefs creates a file system image from a given directory tree.
17 the following file system types can be built:
19 cd9660 ISO 9660 file system
20 chfs "Chip" file system, for flash devices
21 ffs BSD fast file system
22 msdos MS-DOS `FAT' file system (FAT12, FAT16, FAT32)
23 udf Universal Disk Format file system
24 v7fs 7th edition(V7) file system
26 Support for the following file systems maybe be added in the future
28 ext2fs Linux EXT2 file system
30 Various file system independent parameters and contraints can be
33 - minimum file system size (in KB)
34 - maximum file system size (in KB)
37 - mtree(8) specification file containing permissions and ownership
38 to use in image, overridding the settings in the directory tree
39 - file containing list of files to specifically exclude or include
40 - fnmatch(3) pattern of filenames to exclude or include
41 - endianness of target file system
43 File system specific parameters can be given as well, with a command
44 line option such as "-o fsspeccific-options,comma-separated".
45 For example, ffs would allow tuning of:
47 - block & fragment size
49 - number of blocks per inode
52 Other file systems might have controls on how to "munge" file names to
53 fit within the constraints of the target file system.
58 2 some files couldn't be added during image creation
59 (bad perms, missing file, etc). image will continue
63 Implementation overview:
64 ------------------------
66 The implementation must allow for easy addition of extra file systems
67 with minimal changes to the file system independent sections.
69 The main program will:
70 - parse the options, including calling fs-specific routines to
71 validate fs-specific options
72 - walk the tree, building up a data structure which represents
73 the tree to stuff into the image. The structure will
74 probably be a similar tree to what mtree(8) uses internally;
75 a linked list of entries per directory with a child pointer
76 to children of directories. ".." won't be stored in the list;
77 the fs-specific tree walker should add this if required by the fs.
78 this builder have the smarts to handle hard links correctly.
79 - (optionally) Change the permissions in the tree according to
81 - Call an fs-specific routine to build the image based on the
84 Each fs-specific module should have the following external interfaces:
86 prepare_options optional file system specific defaults that need to be
87 setup before parsing fs-specific options.
89 parse_options parse the string for fs-specific options, feeding
90 errors back to the user as appropriate
92 cleanup_options optional file system specific data that need to be
93 cleaned up when done with this filesystem.
95 make_fs take the data structures representing the
96 directory tree and fs parameters,
97 validate that the parameters are valid
98 (e.g, the requested image will be large enough),
102 prepare_options and cleanup_options are optional and can be NULL.
104 NOTE: All file system specific options are referenced via the fs_specific
105 pointer from the fsinfo_t strucutre. It is up to the filesystem to allocate
106 and free any data needed for this via the prepare and cleanup callbacks.
108 Each fs-specific module will need to add its routines to the dispatch array
109 in makefs.c and add prototypes for these to makefs.h
111 All other implementation details should not need to change any of the
117 In the ffs case, we can leverage off sbin/newfs/mkfs.c to actually build
118 the image. When building and populating the image, the implementation
119 can be greatly simplified if some assumptions are made:
120 - the total required size (in blocks and inodes) is determined
121 as part of the validation phase
122 - a "file" (including a directory) has a known size, so
123 support for growing a file is not necessary
125 Two underlying primitives are provided:
126 make_inode create an inode, returning the inode number
128 write_file write file (from memory if DIR, file descriptor
129 if FILE or SYMLINK), referencing given inode.
130 it is smart enough to know if a short symlink
131 can be stuffed into the inode, etc.
133 When creating a directory, the directory entries in the previously
134 built tree data structure is scanned and built in memory so it can
135 be written entirely as a single write_file() operation.