[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

[bug#41143] [PATCH 1/2] mapped-devices: Allow target to be list of strin

From: Mikhail Tsykalov
Subject: [bug#41143] [PATCH 1/2] mapped-devices: Allow target to be list of strings
Date: Thu, 24 Sep 2020 19:09:57 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Icedove/68.12.0

Hi Ludovic,

On 09.09.2020 23:38, Ludovic Courtès wrote:
diff --git a/gnu/services/base.scm b/gnu/services/base.scm
index 0c154d1c4e..3d09e8220c 100644
--- a/gnu/services/base.scm
+++ b/gnu/services/base.scm
@@ -408,7 +408,10 @@ FILE-SYSTEM."
  (define (mapped-device->shepherd-service-name md)
    "Return the symbol that denotes the shepherd service of MD, a
    (symbol-append 'device-mapping-
-                 (string->symbol (mapped-device-target md))))
+                 (string->symbol (string-join
+                                  (let ((t (mapped-device-target md)))
+                                    (if (list? t) t (list t)))
+                                  "-"))))
To avoid duplicating the (if (list? t) …) everywhere, I propose instead
the following approach:

   1. Rename ‘target’ to ‘targets’ (plural) and likewise for the
      accessor, and agree that it always contains a list;

   2. Rename ‘mapped-device’ to ‘%mapped-device’ and add a
      ‘mapped-device’ backward-compatibility macro that allows for a
      ‘target’ (singular) field and automatically turns its value into a
      list.  See the ‘origin’ macro in (guix packages) for an example of
      how to do that (that macro allows users to specify ‘sha256’ instead
      of ‘hash’).

   3. Add a deprecated ‘mapped-device-target’ (singular) that returns the
      first element returned by ‘mapped-device-targets’.

While this looks like a good idea, doesn't this break code that implements mapped-device and assumes that target is a string. Suddenly passing a string to a mapped-device constructor results in a list passed to open/close. Also, what functions should do if they expect a string but get a list of them? Ignore everything but the first item? Implement mandatory check function? Doesn't this change push complexity out of mapped-device to implementations of it.

Basically, this change will break all current implementations of mapped-devices, so I wanted to hear your thoughts on it before continuing.


reply via email to

[Prev in Thread] Current Thread [Next in Thread]