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03/04: doc: Clarify the Swap Space examples, and include an helper examp


From: guix-commits
Subject: 03/04: doc: Clarify the Swap Space examples, and include an helper example.
Date: Tue, 15 Feb 2022 04:31:47 -0500 (EST)

civodul pushed a commit to branch master
in repository guix.

commit cfa6fdc54c58280e49330438aecfb5046ee9e63a
Author: Josselin Poiret <dev@jpoiret.xyz>
AuthorDate: Sun Feb 6 22:20:45 2022 +0100

    doc: Clarify the Swap Space examples, and include an helper example.
    
    * doc/guix.texi (Swap Space): The examples referred to variables
    defined outside of the snippets, and so were not very informative for
    people without much Guile knowledge.  Instead, refer to mapped-devices
    for the first, and use the new helper
    file-systme-mount-point-predicate for the second.
    
    Signed-off-by: Ludovic Court├Ęs <ludo@gnu.org>
---
 doc/guix.texi | 33 +++++++++++++++++++++++++--------
 1 file changed, 25 insertions(+), 8 deletions(-)

diff --git a/doc/guix.texi b/doc/guix.texi
index a05f073c3d..039b418038 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -15742,22 +15742,39 @@ Linux swap partition by running @command{swaplabel 
@var{device}}, where
 @lisp
 (swap-space
   (target (file-system-label "swap"))
-  (dependencies (list lvm-device)))
+  (dependencies mapped-devices))
 @end lisp
 
-Use the partition with label @code{swap}, which can be found after the
-@var{lvm-device} mapped device has been opened.  Again, the
+Use the partition with label @code{swap}, which can be found after all
+the @var{mapped-devices} mapped devices have been opened.  Again, the
 @command{swaplabel} command allows you to view and change the label of a
 Linux swap partition.
 
+Here's a more involved example with the corresponding @code{file-systems} part
+of an @code{operating-system} declaration.
+
 @lisp
-(swap-space
-  (target "/btrfs/swapfile")
-  (dependencies (list btrfs-fs)))
+(file-systems
+  (list (file-system
+          (device (file-system-label "root"))
+          (mount-point "/")
+          (type "ext4"))
+        (file-system
+          (device (file-system-label "btrfs"))
+          (mount-point "/btrfs")
+          (type "btrfs"))))
+
+(swap-devices
+  (list
+    (swap-space
+      (target "/btrfs/swapfile")
+      (dependencies (filter (file-system-mount-point-predicate "/btrfs")
+                            file-systems)))))
 @end lisp
 
-Use the file @file{/btrfs/swapfile} as swap space, which is present on the
-@var{btrfs-fs} filesystem.
+Use the file @file{/btrfs/swapfile} as swap space, which depends on the
+file system mounted at @file{/btrfs}.  Note how we use Guile's filter to
+select the file system in an elegant fashion!
 
 @node User Accounts
 @section User Accounts



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