Fix verify_dentry()

[wimlib] / README

                                   WIMLIB

This is wimlib version 1.0.4 (October 2012).  wimlib can be used to read,
write, and mount files in the Windows Imaging Format (WIM files).  These
files are normally created by using the `imagex.exe' utility on Windows,
but this library provides a free implementation of imagex for UNIX-based
systems.

                                   WIM FILES

A Windows Imaging (WIM) file is an archive.  Like some other archive formats
such as ZIP, files in WIM archives may be compressed.  WIM archives support two
Microsoft-specific compression formats:  LZX and XPRESS.  Both are based on LZ77
and Huffman encoding, and both are supported by wimlib.

Unlike ZIP files, WIM files can contain multiple independent toplevel directory
trees known as images.  While each image has its own metadata describing a
directory tree and file access modes, files are not duplicated for each image;
instead, each file is included only once in the entire WIM.  Microsoft did this
so that in one WIM file, they could do things like have 5 different versions of
Windows that are almost exactly the same.

Microsoft provides documentation for the WIM file format, XPRESS compression
format, and LZX compression format.  The XPRESS documentation is acceptable, but
the LZX documentation is not entirely correct, and the WIM documentation itself
is very incomplete and is of unacceptable quality.

A WIM file may be either stand-alone or split into multiple parts.

                                   WINDOWS PE

A major use for this library is to create customized images of Windows PE, the
Windows Preinstallation Environment, without having to rely on Windows.  Windows
PE is a lightweight version of Windows that can run entirely from memory and can
be used to install Windows from local media or a network drive or perform
maintenance.  Windows PE is the operating system that runs when you boot from
the Windows installation media.

You can find Windows PE on the installation DVD for Windows Vista, Windows 7, or
Windows 8, in the file `sources/boot.wim'.  Windows PE can also be found in the
Windows Automated Installation Kit (WAIK), which is free to download from
Microsoft, inside the `WinPE.cab' file, which you can extract if you install
either the `cabextract' or `p7zip' programs.

In addition, Windows installations and recovery partitions frequently contain a
WIM containing an image of the Windows Recovery Environment, which is similar to
Windows PE.

                                  NTFS SUPPORT

As of version 1.0.0, wimlib supports capturing and applying images directly to
NTFS volumes.  This was made possible with the help of libntfs-3g from the
NTFS-3g project.  This feature supports capturing and restoring NTFS-specific
data such as security descriptors, alternate data streams, and reparse point
data.

The code for NTFS image capture and image application is complete enough that it
is possible to apply an image from the "install.wim" contained in recent Windows
installation media (Vista, Windows 7, or Windows 8) directly to a NTFS volume,
and then boot Windows from it after preparing the Boot Configuration Data.  In
addition, a Windows installation can be captured (or backed up) into a WIM file,
and then re-applied later.

                                    PROGRAMS

wimlib provides a public API for other programs to use, but also comes with two
programs: `imagex' and `mkwinpeimg'.

`imagex' is intended to be like the imagex.exe program from Windows.  `imagex'
can be used to create, extract, and mount WIM files.  Both read-only and
read-write mounts are supported.  See the man page `doc/imagex.1' for more
details.

`mkwinpeimg' is shell script that makes it easy to create a customized bootable
image of Windows PE that can be put on a CD or USB drive, or published on a
server for PXE booting.  See the main page `doc/mkwinpeiso.1' for more details.

                               COMPRESSION RATIO

wimlib can create XPRESS or LZX compressed WIM archives.  As of wimlib v1.0.3,
the XPRESS compression ratio is slightly better than that provided by
Microsoft's software, while the LZX compression ratio is approaching that of
Microsoft's software but is not quite there yet.  Running time is as good as or
better than Microsoft's software.

The following tables compare the compression ratio and performance for creating
a compressed Windows PE image (disk usage of about 524 MB, uncompressed WIM size
361 MB):

        Table 1. WIM size

                                        XPRESS Compression      LZX Compression
        wimlib imagex (v1.0.2):         145,283,871 bytes       139,288,293 bytes
        wimlib imagex (v1.0.3):         139,288,293 bytes       131,379,869 bytes
        Microsoft imagex.exe:           140,406,981 bytes       127,249,176 bytes

        Table 2. Time to create WIM

                                        XPRESS Compression      LZX Compression
        wimlib imagex (v1.0.2):         18 sec                  49 sec
        wimlib imagex (v1.0.3):         19 sec                  30 sec
        Microsoft imagex.exe:           25 sec                  89 sec


                                  DEPENDENCIES

* libxml2
        This is a commonly used free library to read and write XML files.  You
        likely already have it installed as a dependency for some other program.
        For more information see http://xmlsoft.org/.

* libfuse
        Unless configured with --without-fuse, wimlib requires a non-ancient
        version of libfuse to be installed.  Most GNU/Linux distributions
        already include this, but make sure you have the libfuse package
        installed, and also libfuse-dev if your distribution distributes header
        files separately.  FUSE also requires a kernel module.  If the kernel
        module is available it will automatically be loaded if you try to mount
        a WIM file.  For more information see http://fuse.sourceforge.net/.
        FUSE is also available for FreeBSD.

* libntfs-3g
        Unless configured with --without-ntfs-3g, wimlib requires the library
        and headers for libntfs-3g version 2011-4-12 or later to be installed.
        Versions dated 2010-3-6 and earlier do not work because they are missing
        the header xattrs.h (and the file xattrs.c, which contains functions we
        need).

* cdrkit (optional)
* mtools (optional)
* syslinux (optional)
* cabextract (optional)
        The `mkwinpeimg' shell script will look for several other programs
        depending on what options are given to it.  Depending on your GNU/Linux
        distribution, you may already have these programs installed, or they may
        be in the software repository.  Making an ISO filesystem requires
        `mkisofs' from `cdrkit' (http://www.cdrkit.org).  Making a disk image
        requires `mtools' (http://www.gnu.org/software/mtools) and `syslinux'
        (http://www.syslinux.org).  Retrieving files from the Windows Automated
        Installation Kit requires `cabextract' (http://www.cabextract.org.uk).


                                 CONFIGURATION

Besides the various well-known options, the following options can be passed to
wimlib's `configure' script:

--without-ntfs-3g
        If libntfs-3g is not available or is not the correct version, we can
        build without it.  wimlib will then not be able to apply or capture
        images directly to NTFS volumes.

--without-fuse
        If libfuse or the FUSE kernel module is not available, wimlib can be
        compiled with --without-fuse.  This will remove the ability to mount and
        unmount WIM files.  wimlib_mount() and wimlib_unmount() will fail with
        WIMLIB_ERR_UNSUPPORTED.

--without-libcrypto
        Build in functions for SHA1 rather than using external SHA1 functions
        from libcrypto (part of OpenSSL).  The default is to use libcrypto if it
        is found on the system.

--enable-xattr, --disable-xattr
        Enable or disable support for the extended-attributes interface to NTFS
        alternate data streams in mounted WIMs.  To support these, we require
        the setxattr() function and the attr/xattr.h header be available.  The
        default is to autodetect whether support is possible.

--enable-ssse3-sha1
        Use a very fast assembly language implementation of SHA1 from Intel.
        Only use this if the build target supports the SSSE3 instructions.

--disable-custom-memory-allocator
        If this option is given, MALLOC(), FREE(), CALLOC(), and STRDUP() will
        directly call the appropriate functions in the C library.
        wimlib_set_memory_allocator() will fail with WIMLIB_ERR_UNSUPPORTED.

--disable-verify-compression
        Unless this option is given, every time wimlib compresses a data block
        it will decompress it into a temporary buffer and abort() the program
        with an error message if the decompressed data does not exactly match
        the original data.  This is to find bugs.

--disable-error-messages
        Removes all error messages from the library.  If left in, they still
        have to explicitly turned on with wimlib_set_print_errors() in order to
        see them.  Also, error codes will still be returned regardless of
        whether error messages are printed or not.

        If --disable-error-messages is given, wimlib_set_print_errors() will
        fail with WIMLIB_ERR_UNSUPPORTED if the action is to turn error messages
        on.

--disable-assertions
        Remove all assertions.  Without this option, wimlib will abort() the
        program if an assertion fails.  An assertion failure should only occur
        if there is a bug in wimlib.

--enable-debug
        Include debugging messages.  Only use this option if you have found a
        bug in the library.

--enable-more-debug
        Include more debugging messages.  Only use this option if you have found
        a bug in the library.

                                  PORTABILITY

wimlib has mostly been developed and tested on x86_64 (64-bit) GNU/Linux.

It has been tested on x86 (32-bit) GNU/Linux occasionally.

wimlib may work on FreeBSD.  However, this is not well tested.  If you do not
have libntfs-3g 2011-4-12 or later available, you must configure with
--without-ntfs-3g.  Also, GNU coreutils is needed to run the test suite.  Before
mounting a WIM you need to load the POSIX message queue module (run `kldload
mqueuefs').

wimlib should work on big endian machines but it has not been tested.

There are no plans to port wimlib to Windows since the programming interface on
Windows is very different and Microsoft's imagex.exe is already available.

                                   REFERENCES

The WIM file format is specified in a document that can be found in the
Microsoft Download Center.  There is a similar document that specifies the LZX
compression format, and a document that specifies the XPRESS compression format.
However, many parts of these formats are poorly documented, and some parts have
no documentation whatsoever.  Some particularly poorly documented parts of the
formats have had comments added in various places in the library.  Please see
the code and/or ask me if you have any questions about the WIM file format as it
exists in reality and not as it exists in Microsoft's poorly written
documentation.

The code in ntfs-apply.c and ntfs-capture.c uses the NTFS-3g library, which is a
library for reading and writing to NTFS filesystems (the filesystem used by
recent versions of Windows).  See
http://www.tuxera.com/community/ntfs-3g-download/ for more information.

lzx-decomp.c, the code to decompress WIM file resources that are compressed
using LZX compression, is originally based on code from the cabextract project
(http://www.cabextract.org.uk).

lzx-comp.c, the code to compress WIM file resources using LZX compression, is
originally based on code written by Matthew Russotto (www.russotto.net/chm/).

lz.c, the code to find LZ77 matches (used for both XPRESS and LZX compression),
is based on code from zlib.

A very limited number of other free programs can handle some parts of the WIM
file format.  7-zip is able to extract and create WIMs (as well as files in many
other archive formats).  However, wimlib is designed specifically to handle WIM
files and provides features previously only available in Microsoft's imagex.exe,
such as the ability to mount WIMs read-write as well as read-only, and the
ability to create LZX or XPRESS compressed WIMs.

An earlier version of wimlib is being used to deploy Windows 7 from the Ultimate
Deployment Appliance.  For more information see
http://www.ultimatedeployment.org/.

You can see the documentation about Microsoft's version of the imagex program at
http://technet.microsoft.com/en-us/library/cc749447(v=ws.10).aspx, so you can
see how it compares.

                      GNU/Linux equivalents of WIM format

What's the equivalent way to capture the filesystem of a GNU/Linux operating
system into an archive file?  You have a few options:

SquashFS:
        SquashFS (http://squashfs.sourceforge.net/) provides a compressed,
        read-only filesystem for Linux, and it's probably the closest equivalent
        of the WIM format and better designed.  Although you can't mount
        SquashFS read-write, when wimlib does this for WIM files it's really an
        illusion since the WIM isn't actually modified until the image is
        unmounted.  Multiple top-level images in SquashFS files are not
        supported, although nothing stops you from just putting each image in a
        separate directory.

FSArchiver:
        FSArchiver (http://www.fsarchiver.org/Main_Page) is not widely used, but
        it appears to have some features quite similar to the WIM format.

Tar:
        The well-known tar format can usually capture a UNIX filesystem just
        fine, and compressing the tar file produces a good compression ratio
        (better than WIM, especially if using XZ compression), but there is no
        support for random access, file deduplication, multiple images per
        archive, or extended attributes.

Zip:
        Zip shares some features with WIM but is not designed to store entire
        filesystems.

7z:
        The 7z format has some nice features but is unfortunately not designed
        with UNIX in mind.

                                MORE INFORMATION

See the manual pages for `imagex', the manual pages for the subcommands of
`imagex', and the manual page for `mkwinpeimg'.

As of version 0.5.0, wimlib's public API is documented.  Doxygen is required to
build the documentation.  To build the documentation, run `configure', then
enter the directory `doc' and run `doxygen'.  The HTML documentation will be
created in a directory named `html'.

                                    LICENSE

As of version 1.0.0, wimlib is released under the GNU GPL version 3.0 or later.
This includes the files in the `programs' directory as well as the files in the
`src' directory.

wimlib is independently developed and does not contain any code, data, or files
copyrighted by Microsoft.  It is not known to be affected by any patents.

                                   DISCLAIMER

wimlib is experimental.  Use Microsoft's `imagex.exe' if you want to make sure
your WIM files are made correctly (but beware: Microsoft's version contains some
bugs).

Please submit a bug report (to ebiggers3@gmail.com) if you find a bug in wimlib.

Some parts of the WIM file format are poorly documented or even completely
undocumented, so I've just had to do the best I can to read and write WIMs that
appear to be compatible with Microsoft's software.