RFC: Proposed mtree.5 man page

I'm experimenting with mtree support for bsdtar, which
led me to look for a definitive statement of "the
mtree format."  Not finding one, I cobbled together
the attached draft by pulling details from the mtree.8 pages for
FreeBSD and NetBSD and adding a few choice tidbits from
the source code.

I've also included my proposal for a "#mtree" signature
at the beginning of any mtree file.

My goal is for this to become the defining document
for the mtree format across all current implementations.
In particular, I'm looking for comments from people
knowledgable about the existing mtree tools.

Feedback/comments appreciated,

Tim Kientzle

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.\"     From: _at_(#)mtree.8       8.2 (Berkeley) 12/11/93
.\" $FreeBSD$
.\"
.Dd August 20, 2007
.Dt MTREE 5
.Os
.Sh NAME
.Nm mtree
.Nd format of mtree dir heirarchy files
.Sh DESCRIPTION
The
.Nm
format is a textual format that describes a collection of filesystem objects.
Such files are typically used to create or verify directory heirarchies.
.Ss General Format
An
.Nm
file consists of a series of lines, each providing information
about a single filesystem object.
Leading whitespace is always ignored.
.Pp
When encoding file or pathnames, any backslash character or
character outside of the 95 printable ASCII characters must be
encoded as a a backslash followed by three
octal digits.
When reading mtree files, any appearance of a backslash
followed by three octal digits should be converted into the
corresponding character.
.Pp
Each line is interpreted independently as one of the following types:
.Bl -tag -width Cm
.It Signature
The first line of any mtree file must begin with
.Dq #mtree .
If a file contains any full path entries, the first line should
begin with
.Dq #mtree v2.0 ,
otherwise, the first line should begin with
.Dq #mtree v1.0 .
.It Blank
Blank lines are ignored.
.It Comment
Lines beginning with
.Cm #
are ignored.
.It Special
Lines beginning with
.Cm /
are special commands that influence
the interpretation of later lines.
.It Relative
If the first whitespace-delimited word has no
.Cm /
characters,
it is the name of a file in the current directory.
Any relative entry that describes a directory changes the
current directory.
.It dot-dot
As a special case, a relative entry with the filename
.Pa ..
changes the current directory to the parent directory.
Options on dot-dot entries are always ignored.
.It Full
If the first whitespace-delimited word has a
.Cm /
character after
the first character, it is the pathname of a file relative to the
starting directory.
There can be multiple full entries describing the same file.
.El
.Pp
Some tools that process
.Nm
files may require that multiple lines describing the same file
occur consecutively.
It is not permitted for the same file to be mentioned using
both a relative and a full file specification.
.Ss Special commands
Two special commands are currently defined:
.Bl -tag -width Cm
.It Cm /set
This command defines default values for one or more keywords.
It is followed on the same line by one or more whitespace-separated
keyword definitions.
These definitions apply to all following files that do not specify
a value for that keyword.
.It Cm /unset
This command removes any default value set by a previous
.Cm /set
command.
It is followed on the same line by one or more keywords
separated by whitespace.
.El
.Ss Keywords
After the filename, a full or relative entry consists of zero
or more whitespace-separated keyword definitions.
Each such definitions consists of a key from the following
list immediately followed by an '=' sign
and a value.
Software programs reading mtree files should warn about
unrecognized keywords.
.Pp
Currently supported keywords are as follows:
.Bl -tag -width Cm
.It Cm cksum
The checksum of the file using the default algorithm specified by
the
.Xr cksum 1
utility.
.It Cm contents
The full pathname of a file whose contents should be
compared to the contents of this file.
.It Cm flags
The file flags as a symbolic name.
See
.Xr chflags 1
for information on these names.
If no flags are to be set the string
.Dq none
may be used to override the current default.
.It Cm ignore
Ignore any file hierarchy below this file.
.It Cm gid
The file group as a numeric value.
.It Cm gname
The file group as a symbolic name.
.It Cm md5
The MD5 message digest of the file.
.It Cm md5digest
A synonym for
.Cm md5 .
.It Cm sha1
The
.Tn FIPS
160-1
.Pq Dq Tn SHA-1
message digest of the file.
.It Cm sha1digest
A synonym for
.Cm sha1 .
.It Cm sha256
The
.Tn FIPS
180-2
.Pq Dq Tn SHA-256
message digest of the file.
.It Cm sha256digest
A synonym for
.Cm sha256 .
.It Cm ripemd160digest
The
.Tn RIPEMD160
message digest of the file.
.It Cm rmd160
A synonym for
.Cm ripemd160digest .
.It Cm rmd160digest
A synonym for
.Cm ripemd160digest .
.It Cm mode
The current file's permissions as a numeric (octal) or symbolic
value.
.It Cm nlink
The number of hard links the file is expected to have.
.It Cm nochange
Make sure this file or directory exists but otherwise ignore all attributes.
.It Cm uid
The file owner as a numeric value.
.It Cm uname
The file owner as a symbolic name.
.It Cm size
The size, in bytes, of the file.
.It Cm link
The file the symbolic link is expected to reference.
.It Cm time
The last modification time of the file.
.It Cm type
The type of the file; may be set to any one of the following:
.Pp
.Bl -tag -width Cm -compact
.It Cm block
block special device
.It Cm char
character special device
.It Cm dir
directory
.It Cm fifo
fifo
.It Cm file
regular file
.It Cm link
symbolic link
.It Cm socket
socket
.El
.El
.Pp
.Sh SEE ALSO
.Xr cksum 1 ,
.Xr find 1 ,
.Xr mtree 8
.Sh BUGS
The
.Fx
implementation of mtree does not currently support
the
.Nm
2.0
format.
The requirement for a
.Dq #mtree
signature line is new and not yet widely implemented.
.Sh HISTORY
The
.Nm
utility appeared in
.Bx 4.3 Reno .
The
.Tn MD5
digest capability was added in
.Fx 2.1 ,
in response to the widespread use of programs which can spoof
.Xr cksum 1 .
The
.Tn SHA-1
and
.Tn RIPEMD160
digests were added in
.Fx 4.0 ,
as new attacks have demonstrated weaknesses in
.Tn MD5 .
The
.Tn SHA-256
digest was added in
.Fx 6.0 .
Support for file flags was added in
.Fx 4.0 ,
and mostly comes from
.Nx .
The
.Dq full
entry format was added by
.Nx .