file-systems: Allow users to specify file system UUIDs as strings.

Fixes <http://bugs.gnu.org/19778>.
Reported by Mark H Weaver <mhw@netris.org>.

* gnu/system/file-systems.scm (%uuid-rx): New variable.
  (string->uuid): New procedure.
  (uuid): New macro.
* tests/file-systems.scm: New file.
* Makefile.am (SCM_TESTS): Add it.
* doc/guix.texi (File Systems): Give an example of UUID.

1 files changed, 17 insertions, 1 deletions

diff --git a/doc/guix.texi b/doc/guix.texi
index 7b1d18a151f..ad5b38af31d 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -4963,8 +4963,24 @@ interpreted as a file name; when it is @code{label}, then @code{device}
 is interpreted as a partition label name; when it is @code{uuid},
 @code{device} is interpreted as a partition unique identifier (UUID).
 
+UUIDs may be converted from their string representation (as shown by the
+@command{tune2fs -l} command) using the @code{uuid} form, like this:
+
+@example
+(file-system
+  (mount-point "/home")
+  (type "ext4")
+  (title 'uuid)
+  (device (uuid "4dab5feb-d176-45de-b287-9b0a6e4c01cb")))
+@end example
+
 The @code{label} and @code{uuid} options offer a way to refer to disk
-partitions without having to hard-code their actual device name.
+partitions without having to hard-code their actual device
+name@footnote{Note that, while it is tempting to use
+@file{/dev/disk/by-uuid} and similar device names to achieve the same
+result, this is not recommended: These special device nodes are created
+by the udev daemon and may be unavailable at the time the device is
+mounted.}.
 
 However, when a file system's source is a mapped device (@pxref{Mapped
 Devices}), its @code{device} field @emph{must} refer to the mapped