SQUASHFS-TOOLS 4.6 - A squashed read-only filesystem for Linux

	Copyright 2002-2023 Phillip Lougher <phillip@squashfs.org.uk>

	Released under the GPL licence (version 2 or later).

Welcome to Squashfs-Tools 4.6.  The last release was a year ago, and there are
substantial improvements to the tools in this release.

Please see the INSTALL file for instructions on installing the tools, and the
USAGE-4.6 files for documentation on how to use the tools.

This README will describe the improvements, and has the following sections:

1. Summary of changes
2. Filtering and adding extended attributes (XATTRs)
3. Squashfs filesystems conversion (piping Unsquashfs output to Mksquashfs)
4. Author info

1. Summary of changes
---------------------

1. Extended attribute handling improved in Mksquashfs and Sqfstar

	1.1.New -xattrs-exclude option to exclude extended attributes from files
	    using a regular expression.
	1.2 New -xattrs-include option to include extended attributes from files
	    using a regular expression.
	1.3 New -xattrs-add option to add extended attributes to files.
	1.4 New Pseudo file xattr definition to add extended attributes to
	    files.
	1.5 New xattrs-add Action to add extended attributes to files
	    (Mksquashfs only).

2. Extended attribute handling improved in Unsquashfs

	2.1 New -xattrs-exclude option to exclude extended attributes from files
	    using a regular expression.
	2.2 New -xattrs-include option to include extended attributes from files
	     using a regular expression.
	2.3 Extended attributes are now supported in Pseudo file output.

3. Other major improvements

	3.1 Unsquashfs can now output Pseudo files to standard out.
	3.2 Mksquashfs can now input Pseudo files from standard in.
	3.3 Squashfs filesystems can now be converted (different block size
	    compression etc) without unpacking to an intermediate filesystem or
	    mounting, by piping the output of Unsquashfs to Mksquashfs.
	3.4 Pseudo files are now supported by Sqfstar.
	3.5 "Non-anchored" excludes are now supported by Unsquashfs.

4. Mksquashfs minor improvements

	4.1 A new -max-depth option has been added, which limits the depth
	    Mksquashfs descends when creating the filesystem.
	4.2 A new -mem-percent option which allows memory for caches to be
	    specified as a percentage of physical RAM, rather than requiring an
	    absolute value.
	4.3 A new -percentage option added which rather than generating the full
	    progress-bar instead outputs a percentage.  This can be used with
	    dialog --gauge etc.
	4.4 -mkfs-time, -all-time and -root-time options now take a human date
	    string, in addition to the seconds since the epoch of 1970 00:00
	    UTC.  For example "now", "last week", "Wed Mar 8 05:55:01 GMT 2023"
	    are supported.
	4.5 -root-uid, -root-gid, -force-uid and -force-gid options now take a
	    user/group name in addition to the integer uid/gid.
	4.6 A new -mem-default option which displays default memory usage for
	    caches in Mbytes.
	4.7 A new -no-compression option which produces no compression, and it
	    is a short-cut for -noI, -noD, -noF and -noX.
	4.8 A new -pseudo-override option which makes pseudo file uids and gids
	    override -all-root, -force-uid and -force-gid options.  Normally
	    these options take precedence.

5. Unsquashfs minor improvements

	5.1 New -all-time option which sets all file timestamps to <time>,
	    rather than the time stored in the filesystem inode.  <time> can be
	    an integer indicating seconds since the epoch (1970-01-01) or a
	    human string value such as "now", "last week", or
	    "Wed Feb 15 21:02:39 GMT 2023".
	5.2 New -full-precision option which uses full precision when displaying
	    times including seconds.  Use with -linfo, -lls, -lln and -llc
	    options.
	5.3 New -match option where Unsquashfs will abort if any extract file
	    does not match on anything, and can not be resolved.
	5.4 New -percentage option added which rather than generating the full
	    progress-bar instead outputs a percentage.  This can be used with
	    dialog --gauge etc.

6. Sqfstar minor improvements

	6.1 New -ignore-zeros option added which allows tar files to be
	    concatenated together and fed to Sqfstar.  Normally a tarfile has
	    two consecutive 512 byte blocks filled with zeros which means EOF
	    and Sqfstar will stop reading after the first tar file on
	    encountering them. This option makes Sqfstar ignore the zero filled
	    blocks.
	6.2 A new -mem-percent option which allows memory for caches to be
	    specified as a percentage of physical RAM, rather than requiring an
	    absolute value.
	6.3 A new -percentage option added which rather than generating the full
	    progress-bar instead outputs a percentage.  This can be used with
	    dialog --gauge etc.
	6.4 -mkfs-time, -all-time and -root-time options now take a human date
	     string, in addition to the seconds since the epoch of 1970 00:00
	     UTC.  For example "now", "last week", "Wed Mar 8 05:55:01 GMT 2023"
	     are supported.
	6.5 -root-uid, -root-gid, -force-uid and -force-gid options now take a
	     user/group name in addition to the integer uid/gid.
	6.6 A new -mem-default option which displays default memory usage for
	    caches in Mbytes.
	6.7 A new -no-compression option which produces no compression, and it
	    is a short-cut for -noI, -noD, -noF and -noX.
	6.8 A new -pseudo-override option which makes pseudo file uids and gids
	    override -all-root, -force-uid and -force-gid options.  Normally
	    these options take precedence.
	6.9 Do not abort if ZERO filled blocks indicating end of the TAR archive
	    are missing.

7. Other minor improvements

	7.1 If Mksquashfs/Unsquashfs fails to execute generating the manpages
	    because they have been cross-compiled, fall back to using the
	    pre-built manpages.
	7.2 Add new Makefile configure option USE_PREBUILT_MANPAGES to always
	    use pre-built manpages rather than generating them when "make
	    install" is run.

8. Major bug fixes

	8.1 Following a symlink in Sqfscat or where -follow-symlinks option is
	    given with Unsquashfs, incorrectly triggered the corrupted
	    filesystem loop detection code.
	8.2 In Unsquashfs if a file was not writable it could not add extended
	    attributes to it.
	8.3 Sqfstar would incorrectly reject compressor specific options that
	    have an argument.
	8.4 Sqfstar would incorrectly strip pathname components in PAX header
	    linkpath if symbolic.
	8.5 Sqfstar -root-uid, -root-gid and -root-time options were documented
	    but not implemented.
	8.6 Mksquashfs -one-file-system option would not create empty mount
	    point directory when filesystem boundary crossed.
	8.7 Mksquashfs did not check the close() return result.


2. Filtering and adding extended attributes (XATTRs)
----------------------------------------------------

Mksquashfs, Unsquashfs and Sqfstar have a number of new options which allow
extended attributes (xattrs) to be filtered from the source files or added to
the created Squashfs filesystem.

The -xattrs-exclude option specifies a regular expression (regex), which
removes any extended attribute that matches the regular expression from all
files.

The -xattrs-include option instead specifies a regular expression (regex)
which includes any extended attribute that matches, and removes anything
that does't match.

Examples:

% mksquashfs directory image.sqsh -xattrs-exclude "^user."

Exclude any extended attributes in the User namespace from the Squashfs
filesystem.

% unsquashfs -xattrs-exclude "^user." image.sqsh

As above, but exclude them from the Squashfs filesystem when extracting.

% mksquashfs directory image.sqsh -xattrs-include "^user."

Only include extended attributes in the User namespace in the Squashfs
filesystem.

2.1 Adding extended attributes
------------------------------

Mksquashfs and Sqfstar also allows you to add extended attributes to files in
the Squashfs filesystem using the -xattrs-add option and the Pseudo file "x"
definition.  Both options take an xattr name and value pair separated by the
'=' character.

The extended attribute name can be any valid name and can be in the namespaces
security, system, trusted, or user.  User extended attributes are added to files
and directories (see man 7 xattr for explanation), and the others are added to
all files.

The extended attribute value by default will be treated as binary (i.e. an
uninterpreted byte sequence), but it can be prefixed with 0s, where it will be
treated as base64 encoded, or prefixed with 0x, where it will be treated as
hexidecimal.

Obviously using base64 or hexidecimal allows values to be used that cannot be
entered on the command line such as non-printable characters etc.  But it
renders the string non-human readable.  To keep readability and to allow
non-printable characters to be entered, the 0t prefix is supported.  This
encoding is similar to binary encoding, except backslashes are specially
treated, and a backslash followed by three octal digits can be used to encode
any ASCII character, which obviously can be used to encode non-printable values.
The following four command lines are equivalent, and will add the extended
attribute "user.comment" to all files:

mksquashfs dir image.sqfs -xattrs-add "user.comment=hello world"
mksquashfs dir image.sqfs -xattrs-add "user.comment=0saGVsbG8gd29ybGQ="
mksquashfs dir image.sqfs -xattrs-add "user.comment=0x68656c6c6f20776f726c64"
mksquashfs dir image.sqfs -xattrs-add "user.comment=0thello world"

Obviously in the above example there are no non-printable characters and so
the 0t prefixed string is identical to the first line.  The following three
command lines are identical, but where the space has been replaced by the
non-printable NUL '\0' (null character):

mksquashfs dir image.sqfs -xattrs-add "user.comment=0thello\000world"
mksquashfs dir image.sqfs -xattrs-add "user.comment=0saGVsbG8Ad29ybGQ="
mksquashfs dir image.sqfs -xattrs-add "user.comment=0x68656c6c6f00776f726c64"

The following will add an extended attribute to the file named "Hello_World"
using the Pseudo file "x" definition.

% mksquashfs dir image.sqsh -p "Hello_Word x user.comment=Hello_World"

Again, as above, the following are equivalent:

% mksquashfs dir image.sqfs -p "Hello_World x user.comment=0thello\000world"
% mksquashfs dir image.sqfs -p "Hello_World x user.comment=0saGVsbG8Ad29ybGQ="
% mksquashfs dir image.sqfs -p "Hello_World x user.comment=0x68656c6c6f00776f726c64"

2.2 Filtering and adding extended attributes using Actions
----------------------------------------------------------

Finally Mksquashfs allows extended attributes to be filtered and added to files
using the xattrs-exclude, xattrs-include and xattrs-add actions.

xattrs-exclude(regex), this action excludes any extended attributes matching
the regular expression, for any file matching the action tests.

xattrs-include(regex), this action includes any extended attributes matching
the regular expression, for any file matching the action tests.

xattrs-add(name=val), this action will add the extended attribute <name>
with contents <val>, to any file matching the action tests.

Examples: 

% mksquashfs dir image.sqfs -action "xattrs-exclude(^user.)@true"

This will exclude all extended attributes in the User namespace for all
files (true matches on everything).  It is directly equivalent to
-xattrs-exclude(^user.).

% mksquashfs dir image.sqfs -action "xattrs-exclude(^user.)@type(f)"

This will exclude all extended attributes in the User namespace but only for
regular files.

% mksquashfs dir image.sqfs -action "xattrs-include(^user.)@user(phillip)&&type(f)"

Likewise this will include only extended attributes in the User namespace, but
it will only be applied to regular files owned by user Phillip.

% mksquashfs dir image.sqsh -action "xattrs-add(user.comment=Hello_World)@name(hello*)"

This will add the extended attribute "user.comment" to any file named "hello*".

The following two commands are equivalent:

% mksquashfs dir image.sqsh -action "xattrs-add(user.comment=Hello_World)@pathname(Hello_World)"
% mksquashfs dir image.sqsh -p "Hello_Word x user.comment=Hello_World"


3. Squashfs filesystems conversion (piping Unsquashfs output to Mksquashfs)
---------------------------------------------------------------------------

Sometimes you have an existing Squashfs filesystem which you want to
regenerate using a different set of compression options, such as compression
algorithm, block-size, tail-packing etc.  Or you want to modify some parts of
the filesystem such as excluding files, change ownership etc.

Obviously you have been able to mount the Squashfs filesystem and regenerate
the filesystem by running Mksquashfs on the mounted directory.  But, this
requires root access (which sometimes isn't available).  The only other
alternative until now has been to extract the Squashfs filesystem to an
intermediate uncompressed directory, and then regenerate the filesystem by
running Mksquashfs on that.  This, however, is slow and requires storage to
store the uncompressed filesystem.

Unsquashfs can now output a Pseudo file representing the input filesystem
to stdout, and Mksquashfs can now read a Pseudo file from stdin.  This allows
the output of Unsquashfs to be piped to Mksquashfs.

Some examples follow.

If you had a GZIP filesystem and wanted to convert it to ZSTD, you can do:

% unsquashfs -pf - image.sqsh | mksquashfs - new.sqsh -pf - -comp zstd

If you wanted to change to XZ compression, increase to a 1 Mbyte block size, and
use -tailend packing, you could do:

% unsquashfs -pf - image.sqsh | mksquashfs - new.sqsh -pf - -comp xz -b 1M -tailends

If you only want the directory "foobar" you can tell Unsquashfs to only
extract that:

% unsquashfs -pf - image.sqsh foobar | mksquashfs - new.sqsh -pf -

If you had inadvertantly stored binary ".o" files, you can remove them by
using the new "non-anchored" Unsquashfs exclude file functionality:

% unsquashfs -excludes -pf - image.sqsh "... *.o" | mksquashfs - new.sqsh -pf -

If you want to update all the file timestamps to "now", and make every
file owned by "phillip":

% unsquashfs -pf - image.sqsh | mksquashfs - new.sqsh -all-time now -force-uid phillip -pf -

4. AUTHOR INFO
--------------

Squashfs was written by Phillip Lougher, email phillip@squashfs.org.uk,
in Chepstow, Wales, UK.   If you like the program, or have any problems,
then please email me, as it's nice to get feedback!