guix: Add Docker image export.

* guix/docker.scm: New file.
* Makefile.am (MODULES): Register it.
* guix/scripts/archive.scm (show-help, %options, guix-archive): Add
support for "--format".
* doc/guix.texi (Invoking guix archive): Document it.

1 files changed, 17 insertions, 1 deletions

diff --git a/doc/guix.texi b/doc/guix.texi
index adc7fefcae..e52382e976 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -2394,7 +2394,7 @@ what you should use in this case (@pxref{Invoking guix copy}).
 
 @cindex nar, archive format
 @cindex normalized archive (nar)
-Archives are stored in the ``normalized archive'' or ``nar'' format, which is
+By default archives are stored in the ``normalized archive'' or ``nar'' format, which is
 comparable in spirit to `tar', but with differences
 that make it more appropriate for our purposes.  First, rather than
 recording all Unix metadata for each file, the nar format only mentions
@@ -2410,6 +2410,9 @@ verifies the signature and rejects the import in case of an invalid
 signature or if the signing key is not authorized.
 @c FIXME: Add xref to daemon doc about signatures.
 
+Optionally, archives can be exported as a Docker image in the tar
+archive format using @code{--format=docker}.
+
 The main options are:
 
 @table @code
@@ -2438,6 +2441,19 @@ Read a list of store file names from the standard input, one per line,
 and write on the standard output the subset of these files missing from
 the store.
 
+@item -f
+@item --format=@var{FMT}
+@cindex docker, export
+@cindex export format
+Specify the export format.  Acceptable arguments are @code{nar} and
+@code{docker}.  The default is the nar format.  When the format is
+@code{docker}, recursively export the specified store directory as a
+Docker image in tar archive format, as specified in
+@uref{https://github.com/docker/docker/blob/master/image/spec/v1.2.md,
+version 1.2.0 of the Docker Image Specification}.  Using
+@code{--format=docker} implies @code{--recursive}.  The generated
+archive can be loaded by Docker using @command{docker load}.
+
 @item --generate-key[=@var{parameters}]
 @cindex signing, archives
 Generate a new key pair for the daemon.  This is a prerequisite before