btrfs-progs: document the new all-in-one binary

Signed-off-by: David Sterba <dsterba@suse.com>

Documentation/btrfs.asciidoc

@@ -126,6 +126,11 @@ source distribution.
 removed.
 *btrfs-zero-log*:: moved to *btrfs rescue zero-log*, standalone removed.
 
+For space-constrained environments, it's possible to build a single binary with
+functionality of several standalone tools. This is following the concept of
+busybox where the file name selects the functionality. This works for symlinks
+or hardlinks. The full list can be obtained by *btrfs help --box*.
+
 EXIT STATUS
 -----------
 *btrfs* returns a zero exit status if it succeeds. Non zero is returned in

INSTALL

@@ -82,5 +82,22 @@ The resulting binaries have the '.static' suffix, the intermediate object
 files do not conflict with the normal (dynamic) build.
 
 
+All-in-one binary (busybox style)
+---------------------------------
+
+Since version 5.2 it's possible to build a single binary that can act as other
+standalone tools, based on the file name:
+
+    $ make btrfs.box
+    $ mv btrfs.box btrfs
+    $ ln -s btrfs mkfs.btrfs
+
+The list of built-ins can be obtained by
+
+    $ btrfs help --box
+
+The basic set will always contain: mkfs.btrfs, btrfs-image, btrfs-convert.
+
+
 References:
 * https://btrfs.wiki.kernel.org

README.md

@@ -13,6 +13,7 @@ This repository hosts following utilities:
 
 * **btrfs** — the main administration tool ([manual page](https://btrfs.wiki.kernel.org/index.php/Manpage/btrfs))
 * **mkfs.btrfs** — utility to create the filesystem ([manual page](https://btrfs.wiki.kernel.org/index.php/Manpage/mkfs.btrfs))
+* all-in-one binary in the busybox style with mkfs.btrfs, btrfs-image and other tools built-in ([standalone tools](https://github.com/kdave/btrfs-progs/blob/master/Documentation/btrfs.asciidoc#standalone-tools))
 
 The C and python 3 bindings are provided by a LGPL library **libbtrfsutil** see
 [libbtrfsutil/README.md](libbtrfsutil/README.md) for more.