[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
[bug#41143] [PATCH 1/2] mapped-devices: Allow target to be list of strings
Fri, 25 Sep 2020 16:36:11 +0300
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Icedove/68.12.0
On 25.09.2020 12:34, Ludovic Courtès wrote:
Mikhail Tsykalov <email@example.com> skribis:
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
@@ -408,7 +408,10 @@ FILE-SYSTEM."
(define (mapped-device->shepherd-service-name md)
"Return the symbol that denotes the shepherd service of MD, a
- (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
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.
The intent of what I propose above is (1) to not break existing code,
and (2) to avoid duplicating checks and conversions at every call site.
#1 is achieved by providing a deprecated ‘mapped-device-target’
(singular) procedure, for example.
Does that make sense?
I'm sorry if I didn't make myself clear, but it doesn't seem like
open/close functions even use any mapped-device-* procedures, they just
get passed source and target field directly. What I meant was this
change will require changes to luks-device-mapping, raid-device-mapping
and all other device mappings that users may have implemented in their
To be fair, after thinking about it for a bit, I think that this issue
can be solved by renaming mapped-device-kind and providing compatibility
macros similar to %mapped-device. Still question remains about what
should we do if a list gets passed to a kind that doesn't expect it, but
I think we can just raise an error in macro if that's the case. Does
this sound fine to you?