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https://github.com/vbatts/tar-split.git
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a320d77a6f
Include details about tar compatibility, as well as other aspects that have changed Signed-off-by: Stephen Chung <schung@redhat.com>
199 lines
6.1 KiB
Markdown
199 lines
6.1 KiB
Markdown
# go-mtree
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`mtree` is a filesystem hierarchy validation tooling and format.
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This is a library and simple cli tool for [mtree(8)][mtree(8)] support.
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While the traditional `mtree` cli utility is primarily on BSDs (FreeBSD,
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openBSD, etc), even broader support for the `mtree` specification format is
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provided with libarchive ([libarchive-formats(5)][libarchive-formats(5)]).
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There is also an [mtree port for Linux][archiecobbs/mtree-port] though it is
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not widely packaged for Linux distributions.
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## Format
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The format of hierarchy specification is consistent with the `# mtree v2.0`
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format. Both the BSD `mtree` and libarchive ought to be interoperable with it
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with only one definite caveat. On Linux, extended attributes (`xattr`) on
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files are often a critical aspect of the file, holding ACLs, capabilities, etc.
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While FreeBSD filesystem do support `extattr`, this feature has not made its
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way into their `mtree`.
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This implementation of mtree supports a few non-upstream "keyword"s, such as:
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`xattr` and `tar_time`. If you include these keywords, the FreeBSD `mtree`
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will fail, as they are unknown keywords to that implementation.
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To have `go-mtree` produce specifications that will be
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strictly compatible with the BSD `mtree`, use the `-bsd-keywords` flag when
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creating a manifest. This will make sure that only the keywords supported by
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BSD `mtree` are used in the program.
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### Typical form
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With the standard keywords, plus say `sha256digest`, the hierarchy
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specification looks like:
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```mtree
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# .
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/set type=file nlink=1 mode=0664 uid=1000 gid=100
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. size=4096 type=dir mode=0755 nlink=6 time=1459370393.273231538
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LICENSE size=1502 mode=0644 time=1458851690.0 sha256digest=ef4e53d83096be56dc38dbf9bc8ba9e3068bec1ec37c179033d1e8f99a1c2a95
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README.md size=2820 mode=0644 time=1459370256.316148361 sha256digest=d9b955134d99f84b17c0a711ce507515cc93cd7080a9dcd50400e3d993d876ac
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[...]
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```
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See the directory presently in, and the files present. Along with each
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path, is provided the keywords and the unique values for each path. Any common
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keyword and values are established in the `/set` command.
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### Extended attributes form
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```mtree
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# .
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/set type=file nlink=1 mode=0664 uid=1000 gid=1000
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. size=4096 type=dir mode=0775 nlink=6 time=1459370191.11179595 xattr.security.selinux=6b53fb56e2e61a6c6d672817791db03ebe693748
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LICENSE size=1502 time=1458851690.583562292 xattr.security.selinux=6b53fb56e2e61a6c6d672817791db03ebe693748
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README.md size=2366 mode=0644 time=1459369604.0 xattr.security.selinux=6b53fb56e2e61a6c6d672817791db03ebe693748
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[...]
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```
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See the keyword prefixed with `xattr.` followed by the extended attribute's
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namespace and keyword. This setup is consistent for use with Linux extended
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attributes as well as FreeBSD extended attributes.
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Since extended attributes are an unordered hashmap, this approach allows for
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checking each `<namespace>.<key>` individually.
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The value is the [SHA1 digest][sha1] of the value of the particular extended
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attribute. Since the values themselves could be raw bytes, this approach both
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avoids issues with encoding, as well as issues of information leaking. The
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designation of SHA1 is arbitrary and seen as a general "good enough" assertion
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of the value.
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### Tar form
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```mtree
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# .
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/set type=file mode=0664 uid=1000 gid=1000
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. type=dir mode=0775 tar_time=1468430408.000000000
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# samedir
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samedir type=dir mode=0775 tar_time=1468000972.000000000
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file2 size=0 tar_time=1467999782.000000000
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file1 size=0 tar_time=1467999781.000000000
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[...]
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```
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While `go-mtree` serves mainly as a library for upstream `mtree` support,
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`go-mtree` is also compatible with [tar archives][tar] (which is not an upstream feature).
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This means that we can now create and validate a manifest by specifying a tar file.
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More interestingly, this also means that we can create a manifest from an archive, and then
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validate this manifest against a filesystem hierarchy that's on disk, and vice versa.
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Notice that for the output of creating a validation manifest from a tar file, the default behavior
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for evaluating a notion of time is to use the `tar_time` keyword. In the
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"filesystem hierarchy" format of mtree, `time` is being evaluated with
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nanosecond precision. However, GNU tar truncates a file's modification time
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to 1-second precision. That is, if a file's full modification time is
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123456789.123456789, the "tar time" equivalent would be 123456789.000000000.
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This way, if you validate a manifest created using a tar file against an
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actual root directory, there will be no complaints from `go-mtree` so long as the
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1-second precision time of a file in the root directory is the same.
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## Usage
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To use the Go programming language library, see [the docs][godoc].
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To use the command line tool, first [build it](#Building), then the following.
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### Create a manifest
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This will also include the sha512 digest of the files.
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```bash
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gomtree -c -K sha512digest -p . > /tmp/root.mtree
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```
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With a tar file:
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```bash
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gomtree -c -K sha512digest -T sometarfile.tar > /tmp/tar.mtree
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```
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### Validate a manifest
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```bash
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gomtree -p . -f /tmp/root.mtree
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```
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With a tar file:
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```bash
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gomtree -T sometarfile.tar -f /tmp/root.mtree
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```
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### See the supported keywords
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```bash
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gomtree -list-keywords
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Available keywords:
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uname
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sha1
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sha1digest
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sha256digest
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xattrs (not upstream)
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link (default)
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nlink (default)
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md5digest
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rmd160digest
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mode (default)
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cksum
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md5
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rmd160
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type (default)
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time (default)
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uid (default)
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gid (default)
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sha256
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sha384
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sha512
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xattr (not upstream)
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tar_time (not upstream)
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size (default)
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ripemd160digest
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sha384digest
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sha512digest
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```
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## Building
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Either:
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```bash
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go get github.com/vbatts/go-mtree/cmd/gomtree
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```
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or
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```bash
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git clone git://github.com/vbatts/go-mtree.git
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cd ./go-mtree/cmd/gomtree
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go build .
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```
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[mtree(8)]: https://www.freebsd.org/cgi/man.cgi?mtree(8)
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[libarchive-formats(5)]: https://www.freebsd.org/cgi/man.cgi?query=libarchive-formats&sektion=5&n=1
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[archiecobbs/mtree-port]: https://github.com/archiecobbs/mtree-port
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[godoc]: https://godoc.org/github.com/vbatts/go-mtree
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[sha1]: https://tools.ietf.org/html/rfc3174
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[tar]: http://man7.org/linux/man-pages/man1/tar.1.html
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